-------
The technologies discussed in this report constitute a mix of methods that are well established,
commercially available but still relatively new, and innovative methods that are in the research
stage. In particular, information on innovative and emerging technologies is included to provide
readers with future technology options. Utilities are encouraged to monitor the technological
development for future deployment. Table 2-4 summarizes the status of the various applicable
and potentially applicable technologies.
Table 2-4. Status of Condition Assessment Technologies
Technology
CCTV inspection
Zoom camera
Digital scanning
In-line leak detectors
Acoustic monitoring systems
Electro-scanning
Eddy current testing
(ECT)/Remote field eddy current
(RFEC) l
Magnetic flux leakage
Laser profiling
Ground penetrating radar
Gamma-gamma logging
Infrared thermography
Micro-deflection
Impact Echo/SASW
Ultrasonic Pulse Velocity
Ultrasonic Testing
Guided Wave Ultrasonic Testing
Sonar (ultrasonic profiling)
Status of Application to Condition Assessment of Sewers
Commercially available
Commercially available, new applications under development
Commercially available
Commercially available, but limited applications for wastewater pipes
Commercially available
Under development at pilot scale
Under development at bench scale
Commercially available but not yet applied to wastewater pipe
Commercially available as part of multi-sensor robotic platforms for use in
wastewater collection systems
1 Method discussed in USEPA (2009a).
2.3 Cost
A technology's cost effectiveness or affordability is a key factor in the selection process.
Research indicates that in many situations, it is the utility's budget in combination with an
external requirement (e.g., regulatory or due diligence) that determines whether a condition
assessment technology is affordable (Marlow et al., 2007). Ideally, a cost-benefit analysis will
be performed to determine whether it is a worthwhile investment.
Page 2-12
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A cost-benefit analysis evaluates both the costs and benefits of the condition assessment program
to confirm that its costs do not outweigh its benefits. The costs may include:
• Direct inspection costs (e.g., equipment rental, labor, traffic control, sewer cleaning,
bypass pumping).
• Indirect costs to the utility and other parties of carrying out the inspection:
o Costs of service interruption.
o Customer relations.
o Laboratory expenses (e.g., bench-scale experiments, non-destructive testing of
pipe samples).
• Indirect costs to the utility and other parties for data collection, analysis, and reporting:
o Computer hardware and software expenses.
o Staff training on computer software, data collection, and analytical procedures.
• Labor costs before and after fieldwork for planning.
The anticipated benefits of a condition assessment program are more difficult to quantify and
derive mainly from the reduction in the risk of failure (likelihood and consequences of failure)
and the information that allows maintenance, rehabilitation, and replacement to be carried out on
the most cost-effective schedule. Specific benefits may include:
• Reduced sources of I/I.
• Avoided emergency repair costs.
• Avoided costs of extended service disruptions due to catastrophic failure.
• Avoided restoration costs due to environmental and property damage from catastrophic
failure.
• Avoided public health costs (i.e., injury, death, disease transmission) from catastrophic
failure.
• Improved planning and prioritization of rehabilitation and replacement projects due to
condition assessment information and improved estimates of service life.
• Avoided costs of premature pipe replacement or rehabilitation.
• Customer satisfaction and reduced numbers of complaints.
• Improved service reliability.
Thomson (2008) conducted cost-benefit analyses for inspection of gravity sewers and force
mains. He reported that the cost of gravity sewer inspection is typically low with respect to the
value of the asset. For example, the cost of inspecting a 12-in. diameter sewer at a depth of 13 ft
is less than 1% of the asset value, and the proportion decreases with increasing depth and
diameter of the sewer. Thus, the benefits from inspection of gravity sewers are likely to exceed
costs for all but small-diameter sewers at shallow depths.
For force mains, on the other hand, the cost of inspection is high, with indirect costs (e.g.,
temporary flow bypass, accessing the line) often exceeding the costs of physical inspection. For
smaller lines in less populated areas, the monetary benefits of inspection may be less than the
cost of inspection. In such settings, a "fail and fix" approach may be appropriate. However, the
cost-benefit ratio may change in environmentally sensitive areas. The benefits increase greatly
for larger diameter force mains and urban areas due to the increased risk of major consequences.
Page 2-13
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2.4 Implementation Issues
In addition to selecting a technology appropriate for the pipe size, material, and potential defects
of a system, logistical considerations for implementation can be important. Some of the
implementation issues are described below and again in Chapter 7.
Purchasing vs. Contracting
When considering a new technology, a utility may need to decide whether to invest in the
inspection equipment or to use a contractor. This decision involves considering whether the
long-term need for the technology justifies the expense of purchasing the equipment and
software and of training staff. If several technologies are selected for a comprehensive
inspection and prioritization process, subcontracting at least some of the work may be more
economical. The inspection conducted by contractors may cost more (in the near term) than that
by in-house staff (with extra capacity). In other cases, providing steady work to a contractor
could reduce the cost of inspection in the long run.
Productivity
Inspection rate or measurement speed is a significant driver for cost economy and feasibility of a
technology, particularly if traffic control or bypass pumping is needed. Inspection rate varies
considerably among different inspection technologies. For example, utilities that have adopted
zoom camera technology as part of their sewer inspection strategy have reported inspection rates
of 5,000 to 6,000 ft per day, which are roughly three to four times faster than inspections using
traditional in-line CCTV (USEPA, 2010). Manufacturers of two digital scanning devices
(DigiSewer and Panoramo) claim their devices can inspect pipes at a rate of 69 to 70 ft per
minute (http://www.envirosight.com; http://www.rapidview.com/ ), whereas some of the newer
technologies (e.g., sonar) have inspection rates <20 ft per minute (Thomson et al., 2004).
Electro-scanning proceeds at a rate of 30 ft per minute. More production rates of specific
technologies are provided in Chapters 3 through 6.
Complexity
The relative complexity of operating a condition-assessment device and data analysis is an
important factor in its selection. If advanced training is required to calibrate and operate the
equipment, it may discourage its deployment. Similarly, if the labor or materials associated with
maintaining the equipment are prohibitively expensive, the technology may not be suitable for
wastewater collection systems. Highly specialized data analysis, if required, will add another
level of complexity. Utilities may need to decide whether a technology's level of complexity is
acceptable for the benefits received. If the data output is especially detailed with high quality
and helps achieve the inspection objectives, a utility may be willing to use a more complex
technology.
Durability
The conditions under which sewer assessments are typically performed can be challenging.
Devices must be durable enough to withstand the potentially harsh conditions inside a gravity
sewer or force main (e.g., no lighting, water/air interface, and circular configuration).
Page 2-14
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Equipment must also be sufficiently waterproof to operate in rain or wind. Established
technologies have been engineered for use in the sanitary sewer environment. However,
technologies that are in the research stage will need to be evaluated for their ability to withstand
conditions inside a sanitary sewer.
Equipment Deployment and Pipe Access
Equipment that will be deployed inside a sewer must be portable and sufficiently flexible or
modular to enter through a manhole or similar point of access. It will also require autonomous
traction or a tether and winch system. Equipment to be used for assessment of the pipe exterior
must be portable enough to be installed inside an excavation or similarly confined space.
System-specific or project-specific constraints may cause difficulty in deploying inspection
equipment by conventional methods, hence influencing technology selection. For example, a
landowner may be sensitive to the presence of equipment and field crews and hence it is
important to select the least obtrusive technology possible. Flood zones may restrict access. A
long distance between manholes may exceed the equipment's inspection length capability, or a
curved section of pipeline may be difficult to navigate. Equipment deployment is discussed in
Chapters 3 through 7.
Page 2-15
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3. Screening Technologies
As condition assessment strategies and technologies evolve, the value of rapid screening
methods becomes more apparent. For a utility with limited funds, the ability to conduct a rapid
assessment and pinpoint problems for further investigation provides an advantage in asset
management. Time and funds saved can be devoted to more detailed assessments in problem
areas and to rehabilitation. This chapter provides technical performance information and case
study examples for flow data analysis, zoom camera, and acoustic monitoring systems.
3.1 Flow Data Analysis
Flow data analysis can be used to locate problem areas in a collection system in support of
planning for further assessment or rehabilitation. It is particularly useful in systems where there
are I/I concerns. For example, data from an upstream meter can be subtracted from data taken
from a downstream meter to calculate the net flow contribution from that portion of the system;
unexpected values may signal I/I or leakage. Another option is to measure typical dry weather
flow and compare it to wet weather flow to determine I/I (Mitchell and Stevens, 2005).
The traditional method of viewing flow data is through the use of hydrographs, which reveal
information on pipe conditions upstream of a flow meter. Alternatively, flow data can be viewed
as scattergraphs. A scattergraph is created by plotting flow velocity vs. depth. Manning's
equation can be used to calculate a pipe curve, which represents what the data would look like
under ideal, open-channel flow conditions (Figure 3-1). If a pipe is operating as designed, the
scattergraph will approximate the pipe curve. However, this is often not the case. Deviations
from the pipe curve can be valuable in identifying such hydraulic restrictions as silt or obstacles,
bottlenecks, and negative-grade pipe. The data may also indicate surcharged conditions, SSOs,
and CSOs (e.g., Mitchell and Stevens, 2005; Enfmger and Stevens, 2007). There are different
approaches and assumptions in calculating the pipe curve (e.g., roughness coefficient), some of
which are explored in Enfmger and Schutzbach (2005).
Examples of scattergraphs are provided below. Figure 3-1 shows a normal, unobstructed open-
channel flow in which the flow data match the pipe curve calculated using Manning's equation.
In this example, the pipe is not experiencing obstructions or SSOs and is functioning as
designed.
In Figure 3-2, the data conform to the pipe curve until the pipe becomes surcharged, at which
point the velocity levels off as flow depth increases. In Figure 3-3, the plot of velocity data
(referred to as VFINAL on the y-axis) vs. flow depth (DFINAL on the x-axis) illustrates the case
of a downstream flow blockage. Because water is retained behind the blockage, there are 8 in. of
standing water. The scattergraph, therefore, shows a depth of 8 in. at a flow velocity of zero.
Page 3-16
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ADS ENVIRONMENTAL SERVICES, INC.
Location MUNLSD9C
g.
6.000
4.800
3.600
2.400
UOO
0.000
Manual measurements are
within the green circle.
0.000
Pipe Curve
10.00
All Cols Used
1027:16
20.00 30.00
AVGUDEPTH (275 points) in
16-0ct-1996 00:00:00 to 27-Oct-1996 23:45:00
40.00
50.00
Figure 3-1. Scattergraph representing open channel flow.
Image from Mitchell and Stevens (2005). Reprinted with permission.
Page 3-17
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5.000
4.000
3.000
2.000
1.000
0.000
10/06/95
15:19:06
0.000
Pipe Curve
ADS ENVIRONMENTAL SERVICES. INC.
Location EMARION_EM34
10.00
Calibrations
20.00 30.00
AVGUDEPTH (593 points) in
27-Moy-1994 00:00:00 to 19-Aug-1994 23:45:00
40.00
50.00
Hydraulic Grade Line
Figure 3-2. Scattergraph showing surcharged conditions.
Image from Mitchell and Stevens (2005). Reprinted with permission.
Page 3-18
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Scatter Crraph
SB 29
\ . \ \ \ \ \ X
This 18" pipe vvil have an 8" pool at zero flow
o.co
7.5 10.0
DFINAL(in)
12.5
15.0
175
'^^'- '• '• '•'•'• '•'•'• -;: i::: ::'••.! ^i::::::: rrr;;;r;i:i:j!i:iu:?:!:H'B
Figure 3-3. Scattergraph depicting downstream flow blockage.
Image from Mitchell and Stevens (2005). Reprinted with permission.
The use of flow data analysis with the scattergraph method has resulted in cost savings for
utilities. For example, Mitchell and Stevens (2005) cite the case of a utility in the Pacific
Northwest that had a large basin with poor I/I performance. By subdividing the basin into
smaller basins and employing strategically placed flow meters, the utility was able to eliminate
areas with low I/I, saving $300,000 over what otherwise would have been spent on condition
assessment. Although the utility in this example deployed new meters for the study, valuable
information can be gained from existing data. Most systems conduct flow monitoring, but much
of the flow data information is not used. Analysis of historical flow data using scattergraphs can
be useful for evaluating both asset condition and long-term system performance. If scattergraphs
indicate obstructions or other problems, those areas can be given high priority for condition
assessment.
Page 3-19
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3.2 Zoom camera
Description
Zoom cameras can perform a visual inspection more quickly than conventional CCTV. Like
traditional CCTV inspection, zoom camera inspection involves the generation of still imagery
and/or recorded video imagery of a pipe (e.g., Figures 3-4 and 3-5). However, instead of passing
through the pipe, the camera remains stationary. It is mounted on a truck, crane, pole, or tripod,
and is lowered into a manhole to perform the inspection. Newer zoom cameras can pan 360
degrees, and any pipe entering or exiting the manhole can be inspected. Because the camera
remains stationary, imaging the pipe proceeds quickly. Furthermore, the pipe need not be
cleaned prior to inspection, further reducing inspection time as well as cost. Zoom camera
inspection is not designed to replace conventional CCTV inspection, but rather to screen and
prioritize pipes for further conventional CCTV inspection or cleaning. An inspection crew can
move quickly through a service area and highlight segments requiring more detailed inspection.
Figure 3-4. Zoom camera images of pipes showing structural defects.
Image from Rinner and Pryputniewicz (undated). Reprinted with permission.
Figure 3-5. Zoom camera images showing pipes with O&M defects.
Image from Rinner and Pryputniewicz (undated). Reprinted with permission.
Page 3-20
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Although zoom camera inspection is a very efficient, cost-effective method of manhole
inspection, there are some drawbacks. Like all camera technologies, zoom cameras are only
useful for inspecting gravity sewers because force mains and service laterals do not have the
required access points (manholes). Also, like CCTV, zoom cameras cannot inspect beneath the
fluid in the pipe. Limitations in image resolution, lighting, and optical zoom also pose
challenges. Further details on zoom cameras, including descriptions of some commercially
available cameras, can be found in USEPA (2009a). The following sections discuss zoom
camera performance.
Sight Distance and Mainline Defect Capture
Because a zoom camera remains at a manhole and does not travel through a pipe, a key element
of camera performance is the sight distance (i.e., how far down the pipe the camera can capture
an image). Bainbridge and Krinas (2008) note that the sight distance of zoom cameras is limited
by conditions in the pipe such as bends, major blockages, and protruding services (where a
building lateral extends into a main sewer line). Sight distance also varies with pipe diameter.
Joseph and DiTullio (2003) noted that additional light is needed in larger pipes for proper
illumination. Table 3-1 summarizes the range of reported sight distances.
Table 3-1. Reported Sight Distances for Zoom Cameras
Pipe Diameter
mm (in.)
152 (6)
203 (8)
300 (12)
2,400 (96)
Not specified
Sight Distance
m(ft)
15 (50)
12 to 18 (39 to 59)
45 (147)
100 (328)
30 (98) '
Zoom Camera
Make and Model
CUES-IMX
CUES-IMX
AquaZoom
AquaZoom
Not specified
Reference
Batman et al. (2008)
Rinner and Pryputniewicz (undated)
Joseph and DiTullio (2003)
Joseph and DiTullio (2003)
Bainbridge and Krinas (2008)
1 Average sight distance for 23,566 manhole inspections.
A performance issue directly related to sight distance is the percentage of defects identified by
CCTV inspection that are also documented by zoom camera inspection. It is important for
utilities to know if significant information might be missed by using a zoom camera instead of
CCTV. Because zoom camera inspection of a pipe segment is conducted from both the upstream
and downstream manholes, the defects most likely to be missed are those in the middle section of
the pipe (i.e., farther away from the entry points). To address this issue, Bainbridge and Krinas
(2008) explored the statistical locations of defects in pipes. By examining CCTV data for the
Canadian city of Hamilton, Ontario, the percentage of defects that occur within 20 to 30 meters
(66 to 98 ft) of the manhole was calculated, which is within the sight distance noted for zoom
cameras (Table 3-1). The CCTV data indicated that "on average, 59.44% of defects are found
within 20 meters (66 ft) of manholes and 76.12% are found within 30 meters (98 ft) of
manholes." Joseph and DiTullio (2003) also noted that "about 80% of defects ... are usually
located within the first 15 to 20 m [49 to 66 ft] from the manhole." Although the estimates differ
between these two studies, both suggest that zoom cameras can detect a large percentage of
defects because many defects are located within the commonly referenced zoom camera sight
Page 3-21
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distances. Some possible reasons for the large percentage of defects close to manholes include
vibrations from surface traffic, void areas created by infiltration around a manhole, and structural
damage from vertical movement during cold weather (Joseph and DiTullio, 2003).
Production Rate
A primary benefit of zoom camera inspection over CCTV inspection is the speed with which
major mainline defects can be assessed. A typical zoom camera inspection can cover on the
order of one mile per day, compared to 1,000 to 1,500 ft per day for CCTV. Table 3-2 presents
production rates for zoom cameras, ranging from 4,600 ft per day (Rinner and Pryputniewicz,
undated) to 6,250 ft per day (Batman et al., 2008) when accompanied by manhole inspections. A
rate of 10,000 ft per day was cited by Rinner and Pryputniewicz (undated) if manhole inspections
were not performed at the same time.
Table 3-2. Case Studies on the Use of Zoom Cameras
System
Dallas Water
Utilities, TX
Fairfax, VA
Auburn, MA
Hamilton,
Ontario,
Canada
Unnamed
Mid-Atlantic
utility
(population
>500,000)
Description
Pilot project using the
AquaZoom camera.
85-mile pilot program. Pipes
12 to 72 in. in diameter.
Zoom camera inspected
60,000 ft of sewer and
connecting manholes. System
has 18 mi. of gravity sewer (8
to 36 in.) and 4 mi. offeree
mains.
895 mi. completed at time of
report. (System has 1,632 mi.
of sewer mains.)
Large diameter interceptors
(20 to 60 in.) inspected for
replacement/rehabilitation
needs. Approx. 29,500 ft
reinforced concrete pipe
(RCP), 11, 500 ft asbestos
cement (AC) pipe.
Technical Performance
and Results or
Estimates
Approximately 1 mile per
day. Found that only 2%
of system needed repairs
and 28% needed cleaning
and CCTV inspection.
Approximately 6,250 ft
per day. Found that only
66% of pipe needed
CCTV inspection.
Approximately 4,600 ft
per day. Identified I/I and
O&M issues and
structural and manhole
defects.
Approximately 6,152 ft
per day.1 Level of
accuracy adequate for
screening program.
5,000 ft per day. Detected
structural defects, cracked,
broken, and corroded
pipe. O&M findings:
roots, grease, debris.
Cost
Cost data not
provided.
Zoom camera + in-
line CCTV average
$3. 33 per ft; CCTV
alone average $4.89
per ft (including
cleaning)
$1.00 per ft (with
manholes).
$0.977 perm ($0.29
per ft).2
$2. 19 per ft
Reference
Renfro et al.
(2005).
Batman et al.
(2008).
Rinner and
Pryputniewicz
(undated).
Bainbridge
and Krinas
(2008).
Lee (2005).
1 Estimated from average production rate of 25 manholes per day.
2 Estimated funding requirement calculated for cost/benefit analysis.
Page 3-22
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Comparison of Zoom Cameras
The Plainfield Area Regional Sewer Authority (PARSA), which serves eight New Jersey
communities, completed a series of field tests in the fall of 2006 and the winter of 2007 to
evaluate the performance of three commercially available zoom cameras when inspecting 8-in.
diameter sewer lines (PARSA, 2007). PARSA was looking for an inspection technology that
could rapidly assess the condition of its sewer collection systems. The goal was to evaluate each
camera's ability to inspect a 150-ft segment from manholes with straight or curved channels.
The 8-in. pipe size was selected because it represents approximately 90 % of the 2 million linear
ft of sewer pipe in PARSA's collection systems. As summarized in Table 3-3, PARSA found
two major deficiencies with the zoom cameras. First, the operators had difficulty aiming the
cameras down the center of the pipe and had to continually make adjustments. The PARSA
investigators suggested that a guide is needed to center the camera in the pipe. Second, the
cameras were unable to produce images of acceptable quality for the entire 150-ft segment
inspected. Of the three models tested, the IBAK/Orion model was considered the easiest to use.
Table 3-3. Field Test Results for Zoom Cameras by the Plainfield Area Regional Sewer Authority
(PARSA) in New Jersey
Company/Camera
Field Observations
(8-in. diameter pipe)
Ease of Use
CT Zoom/truck-mounted
zoom camera.
Picture became fuzzy at 30
to 35 ft.
Large camera head made it difficult to position in
an 8-in. manhole channel. Constant repositioning
of the head was required to keep it focused down
the pipe. Joystick control was too sensitive.
CUES-IMX truck-
mounted zoom camera.
Picture became pixilated at
30 to 35 ft.
Light head arrangement made it difficult to
position in an 8-in. manhole channel. Constant
repositioning of the head was required to keep it
focused down the pipe.
IBAK/ Orion camera
head mounted on a hand-
held pole.
Good picture for about 60 ft.
The smaller head size and the ability to keep the
camera focused down the pipe made this the most
user-friendly system.
Data from PARSA (2007). Reprinted with permission.
3.3 Acoustic Monitoring
A camera-based technology such as a zoom camera provides a familiar and valuable type of
screening information (i.e., footage) and is suitable for gravity lines. An alternate screening
method is needed, however, for force mains, which are more involved and expensive to inspect
via camera because they must be taken out of service and drained. Acoustic monitoring provides
a screening alternative for detecting wire breakage in PCCP force mains.
Description
Acoustic monitoring systems may be permanently installed along PCCP force mains to provide
continuous monitoring of the general condition of the pipe, or they may be temporarily installed.
Page 3-23
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Acoustic monitoring systems work by detecting the acoustic signal produced by breaking or
broken pre-stressed wire within pipes. Although the systems do not identify individual defects,
they are useful as screening techniques to determine whether further condition assessment should
be performed. Commercially available systems and vendor contact information are provided in
Appendix A.
Performance
Limited data are available on the performance of acoustic monitoring systems. The case studies
in Table 3-4 indicate that utilities do detect broken wires using acoustic technologies from
continuous monitoring/inspection of stressed PCCP pipes. Monitoring results are used for
determining where additional inspection and rehabilitation might be required.
Table 3-4. Case Histories of Technical Performance of Acoustic Monitoring Systems
Device
Application
(Period of Use)
Technical Performance
Reference
Soundprint®
Acoustic
Monitoring System
by Pure
Technologies
(original model c.
1993 with
hydrophones).
Continuous monitoring of
2,700ftof72-in.
diameter PCCP sewage
force main, built in 1975,
Greater Lawrence
Sanitary District, MA.
(2005).
After six months of monitoring, 10
Class A1 and 18 Class B2 wire breaks
were detected. Acoustic monitoring
results were verified by electro-
magnetic and visual inspections.
Higgins et al.
(2006).
Acoustic Emission
Testing (AET)
System by PPIC.
Inspection of 0.5 mile of
54-in. diameter effluent
force main following two
catastrophic failures.
Main originally
constructed in 1976,
North Shore Sanitary
District, 111. (Dec. 2001).
AET results indicated that pre-stressing
wires in several areas were
deteriorating. Based on these results,
the utility conducted further inspection
using PPIC's remote field eddy current
transformer coupling (RFEC/TC)
inspection system. Inspection results
were used to identify and prioritize
rehabilitation needs and to avoid
pipeline replacement.
PPIC (Undated).
Class A wire breaks are defined as wire breaks that match all acoustic criteria for wire breaks.
Class B wire breaks are defined as wire breaks that match most of the important acoustic criteria for wire breaks.
Page 3-24
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4. Technologies for In-Depth Inspection of Internal Pipe Surface
Screening data or other evidence may indicate the need for high-quality, detailed information on
the internal surface condition of sewers. This can be an especially high priority for pipes where
the consequence of failure is great, such as large-diameter pipes that serve a large area or those in
high-traffic areas where replacement would entail major disruptions. Conventional CCTV
remains a mainstay in the assessment of internal surface conditions, and digital scanning is
emerging as a viable alternative.
4.1 Conventional CCTV
Description
Used for decades, CCTV inspection is the backbone of many utilities' condition assessment
programs. In a recent survey report (Thomson et al., 2004), 100% of survey respondents from
large wastewater utility districts relied on CCTV as their primary method of collection system
inspection. The benefits of CCTV are the ability to (1) inspect gravity sewers that are too small
for human entry and as small as 6-in. diameter, (2) inspect pipe of any material, (3) locate and
describe defects, and (4) create a permanent video record of sewer pipe conditions. It cannot,
however, image the portions of the pipe that are underwater. CCTV also does not provide
structural data on pipe wall integrity or a view of the soil envelope supporting the pipe.
Inspection by CCTV involves conveying the camera through the pipeline using various
technologies such as pushrod cameras (pushcams) and remote-controlled robot crawlers. The
level of optical control on the camera varies. Its ability to pan, tilt, and zoom enables the
operator to gain a full circumferential view of the pipe and is why CCTV has become the
industry standard for sewer inspection. Data obtained from CCTV inspection include:
• Evidence of sediment, debris, and roots.
• Evidence of pipe sags and deflections.
• Off-set joints.
• Cracks.
• Leaks (if infiltration is occurring at the time of inspection).
• Location and condition of service connections.
Performance
As noted above, CCTV technology is limited to viewing the inside surface of a pipe above the
waterline. However, for the portion of pipe that can be viewed, a good-quality CCTV camera
provides a video record of pipe condition and allows the assignment of defect codes. Figure 4-1,
for example, shows a concrete pipe in excellent condition, with no apparent cracks or corrosion.
It has been assigned a NASSCO Pipeline Assessment and Certification Program (PACP)
inspection code of 1 on a scale of 1 to 5, indicating that it is free of defects. The pipe in Figure
4-2 shows substantial corrosion and is in poor shape (Grade 4).
Page 4-25
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The quality of defect identification and pipe condition assessment using CCTV depends on many
factors, including operator interpretation, picture quality, and water level. In terms of benefits, it
is a cost-effective technology and provides the broadest base level of data for condition
assessment. There are several technologies that provide data on the structural condition of the
pipe wall (Chapter 5) and others that can determine the condition of the soil surrounding the pipe
(see Chapter 6). However, CCTV provides valuable information on leaks, the location of service
laterals, and sediment and debris accumulation; it will remain an important inspection tool in any
condition assessment program for wastewater collection systems. Typical inspection rates
achieved with CCTV are discussed in Section 4.2 in comparison to digital scanning rates. The
complementary application of CCTV and laser inspections is discussed in Section 5.1.
TUCSON, AZ.
KULU KfWU
UV66-66 -> BV6<-<
C Circular 33
D7.06.2003
Figure 4-1. Concrete pipe - Grade 1 (excellent).
2 total reaches - 713 linear ft / 0.14 mi. Image from Warner and Fleury (2007). Reprinted with permission.
Figure 4-2. Concrete pipe - Grade 4 (poor condition).
Lined and Unlined Concrete Pipe. Image from Warner and Fleury (2007). Reprinted with permission.
Page 4-26
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4.2 Digital Scanning
Description
Digital scanning is a state-of-the-art camera inspection technology. It has been commonly used
in Europe and Asia for a number of years, but has a limited history of use in North America.
Like conventional CCTV, digital cameras are transported through sewer lines using self-
propelled crawlers. Unlike conventional CCTV systems, digital scanning uses one or two high-
resolution digital cameras with wide-angle (fisheye) lenses in the front (or both front and rear)
section of the housing. This configuration allows the generation of two types of images:
"unfolded" views of the sides of the pipes and circular views down the pipe (similar to CCTV).
Digital scanning is primarily used for gravity lines and can be used with any pipe material. As
with other camera-based technologies, it can only image above the water line. Commercially
available digital scanners and vendor contact information are listed in Appendix A.
Digital scanning provides advantages over conventional CCTV. Its rate of inspection or
production rate is typically 2 to 3 times greater than CCTV. Because it combines a large number
of still digital images, it produces a sharper image than video (Knight et al., 2009). Also, the
unfolded view of the inner pipe surface provides an excellent view of pipe conditions (Figures 4-
3 and 4-4). The primary advantage, however, is the ability to access and assess the inspection
data at a later time. Digital scanning does not rely on the operator panning and tilting to examine
defects in the field because the entire pipe surface is imaged during the inspection and the data
are stored. Inspection progresses quickly in the field, but the defect coding is done later in the
office. Software is available for data reviewers to virtually pan, tilt, and zoom as needed to
better identify defects. The high-quality images permit computer-aided measurement of defects
and objects. Additional information on digital scanning capabilities and models can be found in
USEPA (2009a).
Figure 4-3. Example of side scanning image.
Image from Envirosight, as cited in Livingston and Blackmun (2009). Reprinted with permission.
Page 4-27
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ass stt at M» MI at as :ri m j»« g* i*a as ut »» •• m itj M»
•»« JM
O9 Ht Bt lit nt It* At Ht PI Ht III Ml Ht Ht «'t
Figure 4-4. Example of side scanning results
Image from Hydromax, as cited in Livingston and Blackmun (2009). Reprinted with permission.
Performance
Performance issues for digital scanning are related to its ability to provide reliable images for
different diameter pipes (larger pipes in particular), production rate, and comparison of image
quality with that of conventional CCTV. Due to its limited use in North America, available
performance information is anecdotal in nature.
Thomas Iseley of Indiana University-Purdue University Indianapolis provided background
information on digital scanning development and performance (Iseley, Thomas., Phone call with
author, 2009). Because the technology is relatively new, digital scanning can be expected to
undergo continuing development to enhance its capabilities. As with other camera technologies,
one of the limiting factors of digital scanning is camera resolution. In general, the resolution of
digital scanning decreases as pipe diameter increases, although better lighting can help offset this
limitation to some extent. Sewer scanning and evaluation technology (SSET) was originally
designed for pipes 8 to 12 in. in diameter, but the manufacturer had worked to increase this range
in response to customer needs. Apart from hardware development, current research efforts have
focused on software enhancements for defect recognition and digital defect measurements.
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Depending on the outcome of academic and private sector research, digital scanning may
become a cost-effective option for inspecting pipes when a high level of detail is needed.
Comparison of Digital Scanning and CCTV
A comparison of digital scanning with CCTV can provide utilities with valuable information for
deciding whether to try this new technology. A 2001 study by the Civil Engineering Research
Foundation (CERF, 2001) evaluated the performance and costs of SSET at 13 North American
municipalities. This study was based on the first version of SSET, which is considerably
different from current products (PANORAMO and DigiSewer). The first version of SSET used
a rotating mechanical scanner and a mechanical gyroscope. The second generation SSET system
was fitted with a wide-angle lens, similar to the lens used in DigiSewer. Although SSET is
outdated and no longer produced, an evaluation of this early digital scanning model provides
some useful perspectives on digital scanning technology.
CERF tested SSET on approximately 22,000 ft of sewer pipe and compared the performance to
that of CCTV. The recommended scanning speed is reported to be 1 to 3 m per min. (1,000 to
2,000 ft per day). SSET performed well in pipes constructed of PVC, concrete, and vitrified
clay, but not well in HOPE and cast iron pipe. CERF (2001) extensively compared the SSET
system and CCTV; a few highlights are presented here.
More defects were detected by the SSET system than by the CCTV system. The size and
placement of defects were found to be accurate compared to those detected by CCTV, but the
assessment of defect severity did not always correlate well with those defects identified by
CCTV. In addition, the SSET system did not identify all defects equally well. It had more
difficulty than CCTV with detecting infiltration, corrosion, and ovality. The SSET equipment
was also unable to investigate laterals because the camera does not pan to direct the light into
them. It was, however, able to identify cracks, structural defects, and joints very well.
The image quality provided by the SSET system was evaluated on the basis of a number of
criteria. It was determined that SSET image sharpness was generally good, but coloring and
consistency were generally poor. The presentation of data was considered to be excellent. The
factors that negatively affected quality and accuracy of the SSET system included fog in the pipe
and the dirtiness and depth of the sewage. In other words, cleaner pipes generally resulted in
better imaging, which is true for all camera systems.
The results reported in CERF (2001) were consistent with the experience of the city of
Tuscaloosa, AL. SSET was used to inspect 3,200 ft of pipe per day, as compared to 1,000 to
1,500 ft per day by CCTV. The image quality of the SSET system was better than that of CCTV
(Rowe, Reggie. Phone call with author, 2009).
Stein and Brauer (2004) performed a detailed comparison of the PANORAMO system with the
ARGUS 4 CCTV camera (on behalf of IB AK, the manufacturer of PANORAMO). This
comparative study was performed in Wuppertal, Germany. The 46 pipe sections (totaling
approximately 7,870 ft) that were inspected included concrete pipe, RCP, VCP, and brick-lined
collection systems. The pipes and systems investigated ranged from 10 in. to 40 in. in diameter.
From the inspection results, an average inspection speed of 10.43 ft per min. was calculated for
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the PANORAMO system and 5.22 ft per min. for the ARGUS 4 CCTV system. Inspection
speed was affected by pipe material, diameter, and length; number of stops for photographing
defects (for CCTV); and the number of connections and cleanliness of the sewer pipes.
Setup and takedown times were approximately the same for both systems. However, time spent
in the field differed significantly. The ARGUS 4 CCTV was in operation inside the sewer for
70.9% of the inspection time, compared to 23.2% for PANORAMO. The PANORAMO
equipment has a shorter operation time because the data it collects are not processed in the field.
Forty-seven percent of the inspection time for PANORAMO was spent on data post-processing
in the office. The perspective views from PANORAMO were generally of equal quality to those
obtained by the ARGUS 4 CCTV. Stein and Brauer (2004) found that the ARGUS 4 CCTV
system did a better job of illuminating and capturing 3-D objects such as connections and
manholes because the system's pan and tilt features allow the light source to be better directed.
The optical zoom on the ARGUS 4 CCTV system was considered to be better than the digital
zoom on the PANORAMO because the resolution decreases with increased digital zooming.
The PANORAMO picture quality was poorer in pipes with diameters greater than 20 in.
However, describing the condition of the collection system was easier with PANORAMO
because of its abilities to unfold a view and change the viewing direction and angle (using
imaging software during data post-processing).
These studies indicate that digital scanning provides an alternative to CCTV that saves time in
the field, provides a good image, and is relatively easy to work with in terms of data presentation
and description of defects. As the technology progresses, utilities are encouraged to monitor for
pricing reduction and determine whether the digital scanning technology is a cost-effective
option for detailed defect evaluation.
Example of Utility Experience
Hamilton, Ontario, Canada's ninth largest city (population: 520,000), is one North American
utility that has begun to use digital scanning. The City's collection system handles an average of
420 million liters per day (111 MGD) of wastewater and has a total of 2,700 km (1,680 mi.) of
sanitary, combined, and storm sewers. In 2006, Hamilton was involved in a pilot test using
Blackhawk's SSET system for its sewer pipes. City personnel were pleased with the high level
of detail provided by this technology (Bainbridge, Kevin. Phone call with author, 2009). They
noted that digital scanning had identified more details of pipe defects than CCTV. However, city
personnel commented that the primary drawback with the SSET system was the limit in pipe
sizes for effective detection of defects. The SSET system worked best in smaller pipes and was
not as effective for pipes with diameters greater than about 36 in., although the city's contractor
has since reported to Hamilton that they have successfully used SSET in pipes up to nearly 60 in.
in diameter. With the dissolution of Blackhawk, SSET is no longer manufactured or supported.
4.3 Multi-Sensor Technology
Several researchers (Eiswirth et al., 2001; Kuntze and Haffner, 1998) have proposed combining
two or more condition assessment technologies to detect different types of defects in wastewater
collection systems. This strategy offsets the limitations of using a single inspection technology
and augments the information obtained by camera-based technologies. These multi-sensor
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inspection robots have been commercialized in various forms in Europe, North America, Japan,
and Australia. Commercially available multi-sensor inspection robots include critical sensors
(e.g., CCTV, sonar, and laser scanners). The more innovative sensors (e.g., infrared sensors,
radioactive sensors, and impact-echo hammers) have not been deployed on commercial robots.
Some of the multi-sensor robotic platforms available to assess wastewater collection systems are:
• KARO (Kanalroboter).
• PIRAT (Pipeline inspection real-time assessment technique).
• SAM (Sewer Assessment with Multi-Sensors).
• KURT (Kanal-Untersuchungs-Roboter-Testplattform).
• KANTARO.
The number and type of sensors mounted on these robotic platforms have varied depending on
the potential needs. The initial semi-autonomous prototypes (e.g., KARO and PIRAT),
developed by German and Australian researchers, were equipped with CCTV, 3-D optical
(infrared), ultrasonic (i.e., sonar), laser, and microwave sensors (Kuntze and Haffner, 1998). The
PIRAT system could automatically interpret and categorize the defects found during the
inspection. Both the PIRAT and KARO systems were so-called "two-pass" systems, where the
device would make a first pass to detect candidate defects and then complete a more detailed
second pass inspection to confirm the defects (Ahrary, 2008).
Subsequent versions of sewer inspection robots (e.g., SAM, KURT, and KANTARO) were
autonomous. The prototype SAM system, also developed by German and Australian
researchers, was equipped with numerous sensors including sensors used in KARO as well as an
impact-echo hammer, radioactive sensors (based on gamma-gamma logging), a geo-electrical
sensor for leak detection, and a hydro-chemical sensor to detect groundwater infiltration
(Eiswirth et al., 2001). However, this research team has since changed direction to focus on
digital CCTV applications for sewer condition assessment (Burn, Stewart. Email with author,
2009).
These multi-sensor inspection robots have been commercialized in various forms in Europe,
North America, Japan, and Australia. The commercial versions include critical sensors (e.g.,
CCTV, sonar, and laser scanners); however, some of the more innovative sensors (e.g., infrared
sensors, radioactive sensors and impact-echo hammer) have, for the most part, not been deployed
on commercial robots.
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5. Technologies to Evaluate Pipe Wall Integrity
Structural pipe failure may occur due to defects in the pipe wall, such as cracks, misaligned or
offset joints, deflection, and corrosion. Because camera-based technologies are limited to
examining the interior surface of a pipe, they cannot indicate pipe thickness, quantify pipe
geometry, or demonstrate the potential for leakage when there is no visible infiltration at the time
of inspection. Other methods such as laser, sonar, and electrical scanning are used to evaluate
such features. Also, emerging technologies, such as impact echo, spectral wave analysis, and
ultrasonic testing, are being explored for application to sewer condition assessment.
This section provides a description of the performance and application of these technologies.
For the established methods (i.e., laser and sonar), the reader can refer to previous documents for
additional descriptions and information about currently available vendors (USEPA, 2009a;
USEPA, 2010). For the emerging technologies, this chapter provides descriptions, along with
information about their use in other industries and any exploratory research underway for their
use in wastewater collection systems.
5.1 Laser Profiling
Description
Laser-based pipe inspection allows the detection of changes in pipe shape that may be caused by
deformation, deflection, corrosion, or siltation. Laser profiling generates a profile of the pipe's
interior wall. This technique involves using a laser to create a line of light around the pipe wall.
It can only be used to inspect dry portions of a pipe. To assess the entire internal surface of a
pipeline, the pipe must be taken out of service, drained, and cleaned. Lasers are often used in
combination with other inspection methods, most commonly CCTV or sonar. A listing of
commercially available laser scanners and vendor contact information are provided in Appendix
A.
Laser profiles can be generated in either two or three dimensions. The 2-D lasers, also known as
profiling lasers, are the most common laser technology used in pipe inspection. A 2-D laser
projects a pattern of beams (usually a circle) onto the pipe walls. The light is then detected by a
camera to create the 2-D laser image. The 2-D image can provide information on pipe geometry
(e.g., diameter, perimeter, and cross-sectional area), but it cannot provide information to further
characterize defects in the pipe wall. The accuracy of 2-D images depends upon the proper
calibration of the camera and the alignment of the laser with the cross section of the pipe.
Dettmer et al. (2005) reported that the relative positioning of the laser scanner may lead to
difficulties in image interpretation. For example, under certain circumstances, it is not possible
to tell whether a robot has changed position or the pipe has changed position or shape. If the
robot strays from the longitudinal axis and is at an angle, the cross-section of the pipe may
erroneously appear to be oval. Dettmer et al. (2005) presented suggestions for correcting
inaccurate laser profiles.
A new generation of laser-based pipe inspection technologies, 3-D lasers are based on the
principles of laser detection and ranging (LADAR). LADAR-based systems use point laser-
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beams and have a built-in receiver and a two-way transmitter. Unlike 2-D systems, which
produce pipe profiles or cross-sectional views, these systems produce 3-D views of entire pipe
segments. The 3-D LADAR system can also develop accurate cross sections of a pipe even
when the scanner is not directly aligned with the pipe's longitudinal axis. RedZone (undated)
recommends using 2-D laser profiling for pipes with diameters less than 36 in. because the 2-D
profile is sufficiently accurate for pipe this size and is less expensive than 3-D technology. For
larger pipe, 3-D LADAR scanners are recommended. Figures 5-1 (a) and (b) show 2-D and 3-D
laser images, respectively.
Figure 5-1. (a) Two-dimensional (2D) laser profile and (b) Three-dimensional (3D) laser profile.
Image from RedZone (undated). Reprinted with permission.
Performance and Use with CCTV
The case studies presented below reflect the experiences of two organizations, RedZone
Robotics, Inc. and CUES, Inc. Although these case studies provide a limited perspective, useful
information is provided on how this technology can be used and where performance information
can be found given that independent studies by third parties have yet to be done.
Thayer et al. (2009) reported on the technical performance of 3-D LADAR technology instead of
a mandrel to verify the proper installation of flexible pipelines. (A mandrel is a circular device
that is pulled through a pipe to test its shape. It is physically stopped by any deviation from
circularity.) The 3-D LADAR technology was used in Georgetown, Texas, to better understand
the geometry of a newly installed interceptor and to establish a baseline for future inspections.
The project included the inspection of 24,554 linear ft of 30-, 36-, and 42-in. centrifugally cast
glass fiber pipe (CC-GFP). An initial inspection to test a line and verify baseline performance
was conducted using a mandrel and a 3-D LADAR system. The 3-D LADAR measurements
were found to be accurate to within 1/16 in. The inspection identified five pipe segments that
exceeded the 5% deflection limitation for CC-GFP requiring repairs. City personnel noted that
the "three-dimensional LADAR proved to be a valuable and viable method for installation
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verification of flexible pipelines subject to acceptance criterion based on internal geometric
deflection."
Laser profiling is often used with other inspection methods, most commonly CCTV or sonar.
RedZone (2008a) recommended the use of lasers and CCTV when inspecting large pipes
because together these technologies produce complementary data that provide more accurate and
comprehensive information on pipe condition. For example, laser profiling can detect small
changes in pipe geometry (e.g., ovality) that are difficult to detect in a CCTV video image.
Laser-based images can also be used to verify defects observed by CCTV and provide details on
the size and shape of those defects. On the other hand, CCTV can be used to detect fine cracks
and other non-geometric defects that do not appear in the laser images. The additional inspection
costs incurred when using both technologies are offset by the cost savings associated with better
defined rehabilitation projects.
To illustrate the benefits of a combined laser/CCTV inspection, RedZone (2008a) examined the
results of inspections at four locations in which CCTV and lasers were used. Based on 10,000 ft
of inspection data, the laser detected about three defects per 100 ft and CCTV detected about two
defects per 100 ft; however, the two technologies usually identified different defects. In other
words, the net result was that the combined CCTV and laser inspections nearly doubled the
available pipe defect information.
Several other case studies further illustrate how CCTV and laser inspections together can provide
complementary and comprehensive pipe condition information (RedZone, 2008a). In one case,
laser data were used to discount pipe defects originally identified by CCTV inspection. A well-
qualified CCTV operator observed a number of structural problems in a pipe, including multiple
fractures and a single hole. The corresponding laser data did not confirm the presence of these
defects. It was determined that lighting was responsible for the apparent pipe wall fractures and
the hole was really a mirage created by shadows. The additional condition assessment
information provided by the laser data helped the owner save hundreds of thousands of dollars
by avoiding costly and unnecessary rehabilitation work.
In another case, a municipality performed an inspection to assess the quality of a cured-in-place
pipe (CIPP) liner. A CCTV inspection revealed a number of blisters, a known installation defect
with these liners. The corresponding laser inspection was able to provide the exact height, width
and length of each blister, information needed to analyze the severity of the situation and
facilitate repairs.
In a third example, laser scans showed inches of material loss along the walls of the pipe near the
flow line. The laser scans showed a distinct pattern that clearly resembled the rebar present in
RCP. However, closer analysis of corresponding CCTV images determined that the grid pattern
was caused by an exposed layer of brickwork. Ultimately, the "reinforced" concrete pipe was
determined to actually be a brick pipe with a layer of mortar applied later. The CCTV
information helped the asset owner formulate a more appropriate and intelligent rehabilitation
program.
Bennett and Logan (2005) presented three additional case studies in which the ClearLine Profiler
(CUES, Inc.) was used to evaluate pipes with diameters of 6 to 88 in. Moving at the
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recommended speed of 30 ft per min., the ClearLine Profiler captures a laser image every 0.2 in.
Using the requisite software, a utility can determine the pipes' ovality, capacity (cross-sectional
area), and diameter. Highlights from the three case studies are presented below.
The city of Portland, Ore., needed to determine the degree to which a CIPP liner became
distorted after imploding during installation. Bennett and Logan (2005) used graphs of minimum
and maximum diameters of the pipe to evaluate the liner's condition. The results showed that
the liner deviated substantially from the expected internal diameter and was considered to have
"serious deformation." Figure 5-2 shows a ring of light with clear deviation from circularity.
The ClearLine Profiler was able to measure the deformation to a tenth of an inch. City personnel
were able to determine where the liner needed to be replaced, thus avoiding the need to replace
the entire length of liner.
Figure 5-2. Examples of laser profiling for Portland, Oregon.
Image from Bennett and Logan (2005). Reprinted with permission.
The New Zealand city of Tauranga used laser profiling to determine the degree of corrosion
caused by hydrogen sulfide attack in a 24-in. gravity main (Bennett and Logan, 2005). Software
was used to map the laser scan data to a flat graph, similar in concept to the unfolded view used
in digital scanning. The graph used colors to indicate topography, showing where the radius had
a different value than expected. In addition, a capacity graph was used to display cross-sectional
area as a function of distance. The graphic results could pinpoint the locations of corrosion
damage (e.g., a 6.3-in. hole that had been missed by CCTV). Laser scanning was also used in
Auckland, New Zealand, to find corrosion as part of a pipe characterization project conducted in
anticipation of pipe rehabilitation (Bennett and Logan, 2005). Ten mi. of 88-in. sewer main were
scanned. The flat graph and capacity graph showed areas where corrosion had changed the pipe
circumference. The utility used this information to better evaluate rehabilitation needs and saved
more than $10 million in rehabilitation costs over 10 years.
5.2 Sonar
Description
Sonar is used to inspect pipe surfaces below the water line and to map the accumulation of debris
and sediment in sewers > 12 in. in diameter. Sonar can also provide information on pipe
geometry, pipe wall deflections, pits, voids, and cracks. This technology can be applied to
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gravity sewers and sewage force mains made of any material. One benefit is that it can be
deployed in pressurized force mains without taking them out of service. A number of units are
commercially available for wastewater applications. Several case studies, summarized in Table
5-1, highlight sonar's ability to evaluate a pipeline's sediment buildup, physical shape, and
structural condition and corrosion levels. Information on commercially available sonar models
can be found in USEPA (2009a). Figures 5-3 and 5-4 show examples of sonar output. In Figure
5-3, pipe wall thickness and deviations from ideal diameter can be seen. Data are shown in cross
section and longitudinal views. In Figure 5-4, 9 in. of silt can be seen at the bottom of the pipe
where the image deviates from circularity. Figure 5-5 shows the results of a combined sonar and
CCTV scan. The horizontal bar shows deviations in wall thickness indicative of corrosion; red
and orange areas show greater corrosion. The cross sectional view shows sediment at the bottom
of the pipe.
Figure 5-3. Typical sonar results.
Image from Hydromax, as cited in Livingston and Blackmun (2009). Reprinted with permission.
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Figure 5-4. Sonar results of a 30-inch line.
Image from Hydromax, as cited in Livingston and Blackmun (2009). Reprinted with permission.
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Page 5-37
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Figure 5-5. Combined sonar and CCTV results of a 42-in. RCP pipe.
Image courtesy of Hydromax. Reprinted with permission.
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Performance
Acoustic frequency is an important criterion in selecting a sonar device because it affects image
sensitivity and power requirements (Andrews, 1998). As the acoustic frequency and resolution
increase, the background "noise" tends to decrease; however, signal loss also tends to increase
with increases in acoustic frequency, resulting in less penetrating power. Andrews (1998) (Table
5-1) found that a frequency of 2 MHz was suitably accurate to provide information on a sewer's
interior shape; however, the same device provided limited information on structural condition
and wall thickness because the higher frequency pulse was unable to penetrate the pipe surface.
Typically, lower frequency units are used to obtain structural information because they have
greater penetrating power. For most pipe inspections, single frequency sonar units are used.
Table 5-1. Case Histories of Technical Performance of Sonar Devices
Device
Application
(Inspection Period)
Technical
Performance/Results
Reference
Multi-frequency sonar
scanner mounted on RedZone
track-mounted robotic
platform along with other
sensors. Frequency range 650
KHz to 2 MHz.
Inspection of 17,300 ft of 96-
in. diameter RCP, built in
1984. Trinity River
Authority, Texas (Fall 2008).
Sonar data were used to
estimate pipe cross-
sectional area and
sediment volume.
Hines et al.
2009.
High frequency (2 MHz)
rotating sonar transducer
(make and model not
specified) mounted to a pipe
crawler or floating platform.
Inspection of 10,000 m (6.2
mi.) of 1.8 to 2.6m (6 to 8.5
ft) diameter brick-lined
interceptor, built in 1908,
Toronto, Canada (1995).
The brick lining was
found to be in good to
very good condition
except in several isolated
areas. Brick-to-concrete
interface was found to be
in good condition.
Andrews, 1998.
High frequency (2 MHz)
rotating sonar transducer
(make and model not
specified).
Inspection of 15 km (9.3 mi.)
of 2.1 and 2.4 m diameter
(6.9 and 7.9 ft), 35m (114.8
ft) deep, fully surcharged
concrete lined tunnel, built in
1959 in Ottawa, Canada
(1996).
Sonar images showed pipe
invert well scoured but no
significant sediment
buildup. The sewer cross
section was found to be
7% to 9% larger than the
theoretical design value.
High frequency (2 MHz)
rotating sonar transducer
(specific make/model not
specified).
Inspection of 9 km (5.6 mi.)
of 1.5m (60 in.) to 2.6m
(102 in.) diameter concrete-
lined tunnel built in late
1950s and located in an area
of heavy industry in
Hamilton, Ontario (1995).
Sonar images showed no
significant chemical
corrosion as expected
from heavy industry in the
area. Some structural
distortion was observed.
CCTV inspection
confirmed sonar findings.
RedZone (2008b) emphasizes the importance of a sonar device that can adjust to changing
conditions (a common occurrence in a live sewer) and still provide good-quality data. A multi-
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frequency sonar unit can be used to meet a utility's specific information needs despite varying
pipe conditions. For example, different frequencies may be required to accurately evaluate extra
large pipes, multiple pipe materials, and pipes carrying highly turbulent water or large amounts
of suspended solids. In addition, a utility can use a multi-frequency sonar unit to scan a pipe
segment at multiple frequencies to better characterize features and objects such as debris,
blockages, and pipe wall deformation.
Andrews (1998) found that a sonar device's travel rate through the sewer affects the precision of
the results. A "practical" speed of advancement, such as 100 mm per second (4 in. per second),
allows for the optimal identification of critical defects but prevents the detection of very small
defects. The precision of sonar results and image quality are also affected by the quantity of
suspended solids and debris, air entrainment from incoming flow, and the degree of turbulence in
the pipe.
5.3 Leak Detection Systems
Description
Leak detectors are devices used to detect the sound or vibration produced by leaks in pressurized
waterlines or in sewers. The different types include 1) hand-held listening devices such as
listening rods, underwater microphones (also known as aqua phones, sonoscopes, water phones,
or hydrophones), and geophones (ground microphones); 2) leak noise correlators; and 3) in-line
devices, which collect information on leaks remotely. Listening devices and leak noise
correlators are widely available and have been used for leak detection for decades. In-line leak
detectors are a more recent advancement.
The most complex leak detectors are in-line systems, which are deployed in a pipeline and
continuously monitor leakage. There are several commercially available models. Regional and
national providers of leak detection systems and services can evaluate wastewater systems,
although the technology is far more often used for condition assessment of water distribution
systems. Commercially available systems are described in USEPA (2009a).
Performance
The technical performance of leak detection systems in wastewater pipelines was documented in
several case studies (Table 5-2). These investigations were conducted on sewer force mains (12
to 66 in. in diameter) and inverted siphons (12 to 54 in. in diameter). In wastewater force mains,
the leak detectors are not only used to detect leaks, but also to identify air or gas pockets where
hydrogen sulfide gas can collect and corrode the pipe.
Based on simulated leakage tests, Derr et al. (2009) found that the Sahara® leak detection system
could detect active leaks and air pockets in sewage force mains. The study also showed that
water velocity is a critical factor in deploying acoustic systems. Although the Sahara® leak
detection system has been used at lower velocities, Derr et al. (2009) recommended a minimum
of 1.0 fps for straight pipe segments and a velocity of 1.5 fps to provide sufficient energy for
sensor operation in complex sewer systems with vertical bends. In general, an average velocity
greater than 2.0 fps is suitable for deployment in all types of piping systems (Pure Technologies,
2007).
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Knight et al. (2007) presented findings from two case studies of the Sahara® leak detection
system in North America. The studies demonstrated the ease of deployment while sewers
remained in service; however, no leaks were identified, so the system's sensitivity could not be
evaluated. Laven et al. (2008) used the Sahara® leak detection system to inspect a 66-in.
diameter force main after its partial failure and found no other leaks in the 8.5-mile pipeline.
They also conducted two leak simulation exercises to verify that the Sahara® system could
detect leaks in force mains operating at pressures between 10 and 30 psi (Table 5-2).
Pure Technologies (2009a; 2009b) documented the use of the SmartBall™ Leak Detector for
detecting gas pockets in sewage force mains; in both cases, leak detection could not be
confirmed because the line pressure of 15 psi was below the equipment's threshold. In Grand
Forks, N.D., sensors were deployed at 15 different sites to help pinpoint the location of gas
pockets and other detected anomalies. Equipment was extracted using two techniques: by the
standard under-pressure net extraction and by removal at the trash rakes inside the treatment
plant. The system detected gas pockets, but leak detection could not be confirmed because of
low pressure in the line. In San Jose, California, the SmartBall™ equipment was inserted into
the pipeline using pigging facilities at a sewage lift station and removed at the trash rakes inside
the treatment plant (Pure Technologies, 2009b). Fourteen gas pockets were detected, ranging
from 5 to 500 ft in length; no leaks were detected. This technology shows promise, but
information from case studies is limited; systematic study by third-party organizations is needed
to further verify its performance in detecting leaks.
Table 5-2. Case Histories of Technical Performance of Leak Detection Systems
Device
SmartBall™ Leak
Detector by Pure
Technologies.
SmartBall™ Leak
Detector by Pure
Technologies.
Application
(Inspection Period)
Inspection of 8.7 mi. of
24-in. and 36-in. PCCP
and PVC sewage force
mains, Grand Forks, N.D.
(Oct. 2008).
Inspection of 8,533 ft of
24-in. ductile iron (DI)
sewage force main, San
Jose, CA. (Nov. 2008).
Technical Performance
Survey was completed in two days in
10.5 hours run time and a line pressure
<15 psi. The average flow velocity
was 1.0 fps with a maximum velocity
>10 fps. The system detected six gas
pockets ranging from 2 to 18 ft in
length. Leak detection could not be
confirmed because line pressure was
less than the threshold (15 psi).
Survey was performed in 61 minutes
at a line pressure of 15 psi. The system
detected 14 gas pockets ranging from
5 to 500 ft long. No leaks were
detected.
Reference
Pure
Technologies
(2009a).
Pure
Technologies
(2009b).
Page 5-41
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Device
Application
(Inspection Period)
Technical Performance
Reference
Sahara® Leak
Location System
by Pressure Pipe
Inspection
Company (PPIC).
Pilot-scale investigation
including leak simulation
tests of 3 mi. of sewage
force mains (30-in., 42-in.,
48-in. PCCP; 16 in. AC
pipe; 24-in. DI pipe; 20-in.
PVC pipe; and 20-in. CI
pipe) for Hampton Roads
Sanitation District, Va.
(Sept. 2008). Sewage pipe
age ranges from 1 to 85
years with average age of
43 years.
Equipment deployment and retrieval
were successful in pipelines with
velocities >1.5 fps for pipelines with
numerous bends; velocities as low as
1.0 fps were sufficient for relatively
straight pipe segments. The system
was found to detect active leaks and
air pockets. First round pilot testing
costs were $6.25 per ft including
mobilization, field set up, inspection,
data analysis, and final report. Second
round pilot test included retesting of
problem areas and a simulated leak
test so costs are not considered to be
typical. Based on pilot program, the
cost of a full-scale leak testing
program would be an estimated $6 to
$8 per ft.
Derr et al. (2009).
Sahara® Leak
Location System
by PPIC.
Two leak simulation
exercises (April 2007) and
inspection (March 2007)
of 8.5 mi. of 66-in.
diameter PCCP sewage
force main, built in 1972,
following pipeline failure
at leaking joint, Muskegon
County, Mich.
Leak simulation exercises confirmed
accuracy of leak location system: all
simulated leaks identified (1.6 and 14
gallon per hour). The pipeline
inspection revealed no further leaks in
the pipeline following its partial
failure.
Laven et al.
(2008).
Sahara® Leak
Location System
by PPIC.
Case Study 1: Inspections
on 1,995 ft of 12-in. AC
force main, 3,914 ft and
446 ft of two 12-in. steel
inverted siphons, and 256
ft of 28-in. diameter
inverted siphon in
Calgary, Alberta (August
2006). Pipe age not
provided.
Surveys were completed without
major complications and exceeded
anticipated survey distance and
number of siphons inspected within
project budget. Significant electrical
noise observed in one survey was
eliminated by repeating the survey
with a new acoustic sensor. This
system located one air pocket.
Knight et al.
(2007).
Case Study 2:
Inspections on 30 to 54-in.
DI inverted siphons, utility
location not named (2006),
pipe age not provided.
Surveys were completed in 4 of 5
siphons without complications. In the
54-in. diameter siphon, the instrument
could not be deployed more than 31 ft
due to a blockage of debris in the line
and inadequate hydraulic conditions.
No leaks were identified in the
surveys.
Page 5-42
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5.4 Electro-Scanning
Description
Electro-scanning is based on the conduction of electric current through the material of interest.
In the case of sewer inspection, electro-scanning (i.e., Focused Electrode Leak Location; FELL-
41 for mains and FELL-21 for laterals) measures the current flowing between an electrode on the
ground and a sonde (source of current) that moves through the pipe. Non-ferrous pipe materials
(e.g., clay, concrete, and PVC) act as electrical insulators, and voltage only flows through
defects. Therefore, an area with defects has a high current density, which can be detected by the
electrode on the surface. Because water is needed to conduct the current, the pipe must be filled;
a sliding plug is often used to hold water in the pipe as the sonde progresses. The electro-scan
data are displayed graphically as a plot of electric current (amps) vs. distance along the pipe (ft),
as illustrated in Figures 5-6 and 5-7. The electric current level indicates the severity of the
defect. For example, a 1 - 4 amp rating is considered equivalent to a small defect; a 4 - 7 amp
rating signifies a medium defect, and >7 amps indicates large defects (Wilmut and D'souza,
2010). Best practices are outlined in ASTM Standard F2550 - 06, Standard Practice for
Locating Leaks in Sewer Pipes Using Electro-Scan—the Variation of Electric Current Flow
Through the Pipe Wall (ASTM International, 2006).
Electro-scanning can discern sites of rainfall-dependent I/I such as joints and service
connections, which are not readily identified through CCTV inspection. It can also identify
exfiltration defects and structural anomalies such as corrosion and cracks. CCTV can generally
detect defects at joints or service connections if there are roots protruding into the defect or water
flowing through it. However, CCTV cannot be deployed during periods of high flow, when
water would be most likely to flow through joint and service connection defects (Harris and
Tasello, 2004). Thus, electro-scanning is potentially valuable for collection systems with known
I/I problems. Based on inspection of more than 150,000 linear ft of pipe, electro-scanning has
produced repeatable results when inspecting the same pipeline under both wet and dry weather
conditions (Wilmut and D'souza, 2010). Additional description of this technology can be found
in USEPA (2009a). Figure 5-6 shows a hypothetical example of a pipe with defects and the
patterns in current that the different defects would produce. For example, a longitudinal crack
would produce a longer anomaly along the chart than a radial crack. An anomaly that lines up
with the location of a joint indicates that the joint is faulty. Figure 5-7 shows processed electro-
scanning data; corrosion results in numerous sharp peaks. Figure 5-8 shows the change in
electric current due to a change of pipe material and illustrates several joint anomalies. Figure 5-
9 shows the increase in current due to a manhole.
Page 5-43
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House etc
X X X X X X X
Faulty Plug placed in pipe
on push rod
Longitudinal
Crack
Sonde placed in pipe
on push rod
House etc
placed in pipe Longitudinal
on push rod Crack
Plug placed in |
on pushi
Figure 5-6. Hypothetical FELL-21 testing and resulting data showing locations of defects.
Image from Dayananda et al. (2007). Reprinted with permission.
Figure 5-7. Example of electro-scanning results showing corrosion/cracks in a RCP pipe.
Image courtesy of Burgess & Niple. Reprinted with permission.
Page 5-44
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10 20 30 40 SO
TO 10 90 100 110 120 130 140 ISO 160 170 1(0 190 200
Distance from Center of Start MHfft
.
fl
fl
Figure 5-8. Current plot showing change in pipe material from truss to clay, faulty services and
joint anomalies.
Image courtesy of Burgess & Niple. Reprinted with permission.
Figure 5-9. Surge of electro-scan current due to a manhole.
Image courtesy of Burgess & Niple. Reprinted with permission.
Page 5-45
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Performance
Case studies that demonstrate electro-scanning performance are presented in Table 5-3 and
briefly summarized in this section.
Table 5-3. Electro-scanning Case Studies
System
Athens/Clarke
County, GA.
Louisville, KY,
and County of
Sacramento, CA.
Redding, CA.
Louisville, KY.
Application
Inspection of eight
segments of 36-in.
RCP interceptors with
total length of 9,200
ft.
Field testing to
compare relative
effectiveness of joint
pressure testing (JPT),
CCTV, and electro-
scanning in gravity
sewers.
Pilot study of main
line sewers to locate
sources of infiltration
on 25,000 ft of 6-in.
and 8-in. pipe.
Pilot testing program
for gravity sewers:
(7.9 - 9.8-in. VCP;
7.9 -11. 8-in. PVC
pipe; 7.9-in. cured in
place pipe (CIPP);
7.9-in. HOPE pipe).
Compared with air
testing and CCTV.
Performance/Results
Numerous anomalies at
joints. Small defects not at
joints may represent hairline
cracks.
Electro-scanning agreed well
with JPT, but predicted 3
times as many joint defects
and 4 times as many
defective service
connections as CCTV.
Electro-scanning found to be
useful in locating important
sources of I/I. Resulting
repairs reduced I/I from 0.45
MGD to 0.24 MGD.
Inspection rates of 3,000 to
4,000 ft per day.
Advantages in identifying
leaks in dry weather,
prioritization by leak
intensity, alternative to air
testing, and good
reproducibility.
Cost
Estimated at
$15,000.
Electro-scanning
less costly than
CCTV.
Cost information
not provided.
Cost information
not provided.
Reference
Moy et al.
(2006).
Harris and
Dobson
(2006).
Harris and
Tasello (2004).
Gokhale and
Graham
(2004).
A number of case studies illustrate how electro-scanning has been used to locate various types of
leaks. For example, Moy et al. (2006) used electro-scanning to help in planning CIPP
rehabilitation in a section of 36-in. reinforced concrete pipe in Athens-Clarke County, GA. Their
scans revealed many anomalies at joints, as well as anomalies caused by structural defects such
as cracks. Small anomalies were interpreted to represent hairline cracks, possibly from
corrosion. The authors found this information useful in designing rehabilitation.
Harris and Tasello (2004) described a case study of electro-scanning in sewers with known
infiltration problems in Redding, California. Previous attempts to locate and remedy sources of
Page 5-46
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infiltration in Redding's system using flow monitoring, CCTV inspection, joint air pressure
testing, and smoke testing had proven to be inadequate. Therefore, a pilot study using electro-
scanning was conducted. The electro-scanning results were verified through direct inspection
and spot repairs, and the leak locations obtained via electro-scanning were found to be accurate.
The study demonstrated that electro-scanning can form the basis of a cost-effective program to
rehabilitate sewers and reduce infiltration.
It is valuable to compare electro-scanning to joint pressure testing (JPT) to verify electro-
scanning results. JPT involves isolating the joint with a device such as a packer and introducing
water or air into the void. Failure to reach a specified water or air pressure indicates pipe
leakage. In a study of eight pipe segments in Kentucky and California, Harris and Dobson
(2006) found that the number of joint defects identified by JPT and electro-scanning agreed
within 4%; out of a total of 419 joints tested, 270 failed the JPT, and 286 joint anomalies were
found by electro-scanning. When JPT was combined with CCTV, the results agreed within 1%
of those obtained by electro-scanning. Based on this study, electro-scanning may be a viable
alternative for JPT, and it was reported to cost only 20% to 25% as much as JPT.
Gokhale and Graham (2004) suggest that electro-scanning may actually be superior to JPT in
finding defects. They participated in a pilot study in which the FELL-41 system showed many
more joint anomalies than JPT. Gokhale and Graham (2004) noted that this discrepancy reveals
a potential problem with air testing. During an air test, packers used to isolate sections of pipe
for testing may force deformed pipes to become rounder and provide a better seal with the
connecting pipes compared to normal field conditions. Therefore, it was concluded that the
results from electro-scanning might be more representative of true pipe condition.
Harris and Dobson (2006) found that electro-scanning detected three to four times as many pipe
defects as did CCTV. For example, based on testing of 59 service connections, CCTV identified
12 defective service connections, whereas electro-scanning found 48 defective service
connections. Defects at joints and service connections are not readily apparent on CCTV unless
water is flowing through them; electro-scanning can locate such "invisible" defects. Although it
is not a replacement for CCTV, electro-scanning may be valuable if deployed in addition to or
before CCTV.
In terms of production speed, Harris and Dobson (2006) reported that the speed of electro-
scanning depends on pipe diameter. The scanning rate for large-diameter pipes is slower than
that for small-diameter pipes. The rates for electro-scanning were similar to those for CCTV
(excluding the time needed to clean the pipe prior to CCTV deployment). Pipe preparation for
electro-scanning includes debris removal, but not complete sewer cleaning. The total time to
inspect 300 ft of 8-in.VCP was estimated to be 45 minutes for CCTV, 190 minutes for JPT, and
35 minutes for electro-scanning.
5.5 Impact Echo and Spectral Analysis of Surface Waves
The impact echo (IE) and spectral analysis of surface waves (SASW) methods measure sound
waves that are generated by a mechanical impact. Both were originally developed for
conventional testing of concrete structures to measure the thickness of cracks and to locate voids.
Although not yet commercially available in the U.S., the IE method, as demonstrated by
Page 5-47
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researchers in Japan, can locate and measure longitudinal and circumferential cracking in
wastewater collection systems. Prototypes have seen limited use in wastewater sewers in Japan
by Sekisui Corporation and in large water supply tunnels in the U.S. by Olson Engineering
(Kamada and Okubo, 2005, Dingus et al., 2002).
According to the Japanese manufacturer, IE can be used in reinforced concrete and clay pipe
with diameters from 8 to 28 in. (200 to 700 mm) (Asano, Masanori. Email with author, 2009).
Research has shown that the technology can only be used in clean pipes with flow depth less
than 20% of the inside pipe diameter. Kamada and Okubo (2005) first tested the IE system,
mounted on a robotic platform along with a CCTV camera, in buried 10-in. (250 mm) diameter
concrete pipes under controlled conditions. The results from the controlled condition study were
used as a reference for field tests of 14-in. (350 mm) diameter concrete sewer pipe. The field
tests showed that the IE technique could identify longitudinal and circumferential cracking in a
pipe.
Impact Echo
The IE technique consists of striking the material of interest with a hammer or similar tool (the
impact) and recording the vibrations of the resulting acoustic response (the echo). The
underlying principle of IE is that the sound waves (the compression waves in particular)
generated by the mechanical impact reflect off cracks, discontinuities, and the outside edges of
the subject material. The reflected sound waves are detected by a receiver and translated into
output, which is interpreted by the operator. Figure 5-10 graphically describes the IE method.
Impact
Transducer
DsaAcquiafion System and
Computer
»
-
Waretorm
S['- l-'.r:
Tune
Frequency
Figure 5-10. Illustration of Impact-Echo method.
Image from Sansalone and Streett (1998). Reprinted with permission.
Page 5-48
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Spectral Analysis of Surface Waves (SASW)
Like the IE technique, the SASW technique measures sound waves that are generated by a
mechanical impact. But unlike the IE technique, which measures compression waves, the SASW
method measures surface waves. (Surface waves travel the surface of a material to a depth of
one wavelength.) This method allows testing over a range of depths (from the surface of
material being tested) corresponding to different wavelengths. The SASW technique provides
information on wave velocity variations over the depth of a material, which helps define
individual layers and transitions between layers in the material being tested. Both IE and SASW
are analogous in many ways to seismic profiling techniques used by geophysicists to detect
subsurface structures.
Equipment
The equipment requirements for IE and SASW are similar. Both methods require a mechanical
impact tool, a displacement transducer (or accelerometer), and a computer for data acquisition
and signal analysis. Equipment for both conventional and innovative testing is described in the
sections below.
Conventional Equipment
Steel balls or an electrically driven solenoid hammer are typically used to generate the
mechanical impact for the IE method. The steel balls, which are mounted on spring rods, are
selected based on diameter. The duration of the impact (or contact time) of the steel balls varies
with their diameter (Carino, 2001). The impact of the solenoid-activated hammer is moderated
by the voltage in the solenoid (Carino, 2009). The contact time for the steel balls or the solenoid
hammer ranges from 30 to 60 microseconds.
The transducer is in direct contact with the material being tested to detect the reflected sound
waves. A standard transducer measures the displacement (i.e., vibration) at the material surface
and converts the displacement reading into voltage. Many of the commercially available
portable IE testing kits combine the solenoid hammer and transducer into one handheld device.
The conventional equipment for the IE technique has several disadvantages:
1. It is relatively slow for inspecting large surfaces.
2. It requires exposure of a clean surface to allow direct contact of the transducer with
the material surface.
3. It requires relatively clean and dry test conditions.
Innovative Equipment
To overcome the disadvantages of conventional IE and SASW systems, innovative equipment
has been developed, including laser scanners, air-coupled transducers, and robotic scanners. In
particular, transducers have been improved to address problems stemming from the need for
direct contact with test materials.
Page 5-49
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Laser scanners have been used to detect sound waves, with a laser beam projected onto the
material to record vibrations. Because the operation of the laser scanner relies on the smoothness
of the material, the inherent roughness of concrete has limited its application (Zhu and Popovics,
2007). Sometimes paint is applied to the surface to enhance reflection. Laser scanners have
been widely used in the restoration of artwork and historic buildings.
Air-coupled transducers have been proposed by researchers (Zhu and Popovics, 2007) to replace
the conventional IE direct contact sensors. These transducers are composed of small, highly
directional microphones located relatively close to the material to be tested; hence, there is no
need for a fluid or gelatinous substance to couple the transducers to the test material. Air-
coupled sensors used with the IE technique have proved to be effective in locating delaminations
and voids in concrete (Zhu and Popovics, 2007).
Scanners or robots may be used to address the relatively slow production and difficult handling
of the conventional IE point-by-point technique (Grosse et al., 2005). For pavement and wall
testing, scanners have been developed to increase the testing speed. It has also been found that
the data generated using scanners are easier to interpret and less prone to operator error than data
from the point-by-point technique (Colla et al., 1999). Scanners are mounted on the wall or
pavement over the area to be tested and are moved manually and reattached at the next area to be
tested. German and French researchers have developed and extensively tested these scanners on
concrete walls and pavement (Wiggenhauser, 2009).
A recent innovation in SASW techniques is the mobile acoustic device (MAD) prototype system
in which the impact hammer and the air-coupled transducer are mounted on a wheeled cart
(Marzani et al., 2007). Experimental testing on the MAD system was suspended due to lack of
funding (Marzani, Alessandro. Email with author, 2009). Researchers have shown that prototype
mobile devices similar to the MAD system can detect defects in pavement and road sub grade
(Ryden et al., 2009).
Application and Performance in Other Industries
The IE and SASW methods have been used extensively to test engineered structures. When used
on concrete structures, IE has been found to be effective in locating surface delaminations and
voids. These are formed during construction when the mortar does not fill the spaces among the
coarse aggregate particles. The IE method has also been used to measure the depth of surface-
opening cracks and the thickness of structural supports. In Germany, where there are regulatory
requirements for tunnel linings, the IE method has been used extensively for quality control
(Grosse et al., 2005).
In the U.S., researchers have applied IE technology to the condition assessment of large water
mains for the Bureau of Reclamation (Sack and Olson, 2007).
The SASW method has been used to monitor dams and bridges to measure the depth of surface-
opening cracks and freeze-thaw damage and to measure relative concrete quality. SASW has
also been used to profile the thickness of pavement, including asphalt and layer systems for
highways and roads (Olson Engineering, 2007). It has been used to assess the condition of
Page 5-50
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concrete liners in tunnels and large-diameter concrete and brick water lines. But it has not been
applied to wastewater collection systems (Olson Engineering, 2007; Makar, 1999).
5.6 Ultrasonic Testing
Description
Two emerging ultrasonic testing technologies, the ultrasonic pulse velocity method and guided
wave ultrasonic testing, are potentially suitable for the condition assessment of wastewater
collection systems. The ultrasonic pulse velocity method is based on the speed with which an
ultrasonic pulse passes through the test material. Guided wave ultrasonic testing (discussed in
Section 5.7) induces plate or "guided" waves in the material, permitting detection of cracks and
measurement of pipe wall thickness.
Ultrasonic testing assesses the surface as well as the internal features (e.g., thickness and
material properties) of the object being tested. For wastewater sewers, ultrasonic testing can
measure pipe thickness, detect corrosion, and detect and measure cracks. In its simplest form,
ultrasonic inspection uses the pulse-echo method to measure the thickness of materials. The
short burst or pulse is induced in the material using a transducer. The pulse passes through the
material until it reaches the other side, where its echo is reflected to the surface. The duration
and velocity of the pulse are measured and used to determine the distance from the surface to the
outer side. The pulse can also be directed into the material at an angle using an angle beam
transducer. The angle allows for more accurate detection of cracks or flaws in the material. The
conventional ultrasonic testing method typically involves point-by-point measurements along the
surface of the material being tested. To ensure sufficient transmission of sound waves, a
couplant, either water or a gel, must be applied between the sensor and the test material.
Like the IE and SASW methods, the conventional transducers used for ultrasonic testing have
several potential drawbacks:
1. They are relatively slow for inspecting large surfaces due to the required point-by-
point measurements (including the movement of angle beam transducers).
2. They require exposure of a clean surface to allow direct contact of the transducer with
the material surface.
3. They require relatively clean and dry test conditions.
Innovative ultrasonic transducers have been developed to overcome the drawbacks of deploying
conventional transducers in the field. These sensors include phased array (PA) transducers,
electromagnetic acoustic transducers (EMAT), and air-coupled transducers (including lasers).
The PA transducer eliminates the need to move an angle beam transducer across the surface of
the material. The EMAT and air-coupled transducers eliminate the need for direct contact. As a
result, they can increase the speed of ultrasonic inspections and allow testing of some otherwise
difficult surfaces (e.g., coated pipes). Both the PA and EMAT transducers control the "noise"
associated with surface waves so that guided wave inspections can occur (Section 5.7).
Page 5-51
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Application and Performance in Other Industries
Ultrasonic testing of the exterior of pipe walls (on aboveground or excavated portions) has been
common practice in many industrial sectors, including water and wastewater utilities. Ultrasonic
testing equipment is commercially available and has been implemented on ferrous water mains
and wastewater force mains (Thomson et al., 2004; USEPA, 2009b). It has been used under
controlled laboratory and field conditions. It can test most pipe materials including metals,
ceramics, plastics, and composites but performs best on steel and ductile iron pipe (Iowa State
University, 2008). Because the conventional ultrasonic testing method is typically operated from
the outside of the pipe, it can be used on pipes of all sizes.
Ultrasonic testing can also be used to inspect the interior of petroleum liquid pipelines. The
natural gas industry has developed various devices (e.g., liquid-filled transducer wheels and
EMATs) to deploy ultrasonic testing equipment in gas mains. These devices have not been
adapted for wastewater collection systems and water transmission systems due to their high cost
and potential operational difficulties (Marlow et al., 2007).
Though ultrasonic testing has seen widespread use on pipes constructed of homogeneous
materials (i.e., steel pipe), researchers at the University of Waterloo are researching its use on
pipes constructed of heterogeneous materials (i.e., concrete pipe) (Jiang et al., 2006; Lopez et al.,
2001). Ultrasonic testing has also been used to measure the depth of cracks in concrete pipe
(Yang et al., 2009).
5.7 Guided Wave Ultrasonic Testing
Description
Guided Wave Ultrasonic Testing (GWUT), also known as long-range ultrasonic testing, uses
ultrasonic waves to inspect metal pipes (Cawley and Alleyne, 2004). It uses ultrasonic waves at
the lower end of the ultrasonic frequency spectrum (normally below 100 kHz)). GWUT can
detect cracks and measure the wall thickness of a metal pipeline across a large distance. GWUT
is commercially available and has been used on industrial piping in manufacturing and in the oil
and gas sector. It has not been used on wastewater force mains but has been successfully field
tested on water mains in the U.K. (Reed et al., 2004).
Unlike other forms of ultrasonic testing, GWUT testing induces plate-type waves rather than
compression waves in the material being inspected. These plate-type waves are called "guided
waves" because they travel by interacting with the upper and lower surfaces of the plate or pipe
wall. Plate waves can travel long distances (up to 100 meters under some conditions) and can
detect the loss of plate or pipe wall thickness (i.e., erosion or corrosion) and cracks (Edwards,
2006). However, these waves need to be controlled in order to generate a high-quality signal
(Cawley and Alleyne, 2004). GWUT can be used to inspect large surfaces from a single probe,
thereby eliminating the manual movement of the transducer used for conventional ultrasonic
testing.
Like other ultrasonic techniques, GWUT testing requires transducers, a pulser-receiver
(processor), and display equipment. On pipelines, the transducer can be in the form of a wrap-
around collar or a thin ferromagnetic strip sensor mounted on the pipe's exterior (Figure 5-11).
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Figure 5-11. Example wrap-around collar with piezoelectric shear motion sensor (Teletest sensor
collar).
Image courtesy of TWI Ltd (http://www.twi.co.uk/). Reprinted with permission.
Application and Performance in Other Industries
GWUT has been used most often to scan metal pipe in the process, oil, and gas industries for
erosion or corrosion. However, more recent studies using EMAT or PA transducer technology
have used GWUT for defect sizing (Mudge et al., 2007; Rose et al., 2009).
The GWUT technique can be used on a wide range of geometric structures, from the simple
(e.g., pipes and plates) to the more complex (e.g., wire cable, rails in railroads, and sheet piling)
(Edwards, 2006). Because GWUT does not require direct contact with the entire material
surface, it has been widely used to inspect insulated industrial pipe for corrosion. Similarly,
GWUT testing can be used on piping that is inaccessible or located in short sleeves (e.g., road
crossings). Though GWUT has been used for above-ground piping at industrial facilities, it has
also been used for underground piping that can be accessed at some point from an excavation or
aboveground portion (Marlow et al., 2007). This method is used to inspect steel pipe, but it has
not been proven for gray cast iron and ductile iron pipe (USEPA, 2009b). It has been shown to
work best on continuous butt-welded steel pipe (USEPA, 2009b; Lillie et al., 2004).
GWUT reportedly can inspect up to 300 ft of pipe (USEPA, 2009b). On pipe with flanged,
socket-welded, and socket-and-spigot fittings, the length of inspection is limited to the length of
a single spool (Reed et al., 2004). In general, pipes with diameters from 2 to 48 in. and with
walls less than 1.6 in. thick can be inspected with GWUT (USEPA, 2009b; Marlow et al., 2007;
Lillie et al., 2004).
Although it is an effective screening technology, GWUT may miss critical defects and cannot
measure the depth of a defect (Thomson et al., 2004; USEPA, 2009b). GWUT technology can
be improved using PA transducer technology to better detect critical defects and locate
circumferential cracks in pipelines (Mudge et al., 2007; Rose et al., 2009). In research conducted
for the U.S. Department of Transportation, Mudge et al. (2007) confirmed that a proposed wave
focusing technique enhances GWUT so that it can detect corrosion or coating faults on coated or
encased gas pipelines. In a series of laboratory tests and field investigations, PA transducers
were used to focus the ultrasonic waves on piping with diameters ranging from 6 to 20 in. The
study results indicate that wave focusing enhances GWUT to: (1) increase the detection of small
Page 5-53
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defects; (2) decrease the number of false positives; (3) locate a defect at any part of the pipe
circumference; and (4) estimate the defect size.
5.8 Micro-deflection
Description
According to USEPA (2009a), micro-deflection is a non-destructive technology used to evaluate
brick, concrete, and clay structures. The method involves the application of a load onto the
structure to create a slight deformation, called a "micro-deflection." The structure's micro-
deflection is measured and displayed graphically (as a plot of load vs. deflection). Structurally
sound test materials would be expected to have a consistent micro-deflection profile for various
loads, while deteriorated or defective structures would deviate from expected values.
Micro-deflection was used to perform condition assessments of brick sanitary sewers in Montreal
in the mid-1990s (Makar, 1999), but has not been widely used since (USEPA, 2009a). The
usefulness of micro-deflection is limited because it can give only a general understanding of pipe
condition, such as the integrity of joints, rather than identification of individual defects. In
addition, plastics such as PVC and HDPE cannot be inspected using this method. The
technology is still under development (Eldada, M. Victor. Email with author, 2009).
5.9 Fiber Optic
Description
In fiber optic systems, light pulses generated by a laser or light-emitting diode (LED) are
transmitted through thin glass fiber optic lines the diameter of a human hair. Fiber optic sensors
measure the backscattering of the light pulses. Typically, many fiber optic lines are assembled
into a fiber optic cable that is used to monitor strain and temperature changes in structures such
as dams, bridges, and pipelines. Temperature changes are used to detect and locate pipeline
leaks. Changes in strain indicate deflections in the structure, potentially from geologic or
human-induced movements. Wall thickness can be measured by strain sensors on the outside of
the pipe wall (USEPA, 2009b). Fiber optic technology is not currently applied to wastewater
collection systems, but merits investigation due to its success in monitoring oil and gas pipelines
and water mains.
The equipment required for the fiber optic system typically includes a transmitter (either a laser
or LED), the optical fiber itself (usually hardened cable), regenerators (for distances beyond 12 -
15 mi.), and an optical receiver (LxSix, 2007). One optical fiber and data acquisition system can
monitor up to 15 mi. of pipe without regenerators (Higgins and Paulson, 2006). The cost of fiber
optic monitoring of pipelines can be as low as $1 to $2 per meter ($0.30 to $0.60 per ft) for long-
distance pipelines (OzOptics, 2008).
Application and Performance in Other Industries
For structural monitoring of oil and gas pipelines, the fiber optic cable is installed permanently
within a few yards of the pipeline. Various companies, including LxSix, Omnisens, and
Ozoptics, provide proprietary pipeline monitoring systems that use fiber optic distribution strain
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and temperature sensors. The systems can distinguish between pipeline leaks, tampering,
intrusions, and machinery and vehicles operating in the vicinity of the pipeline.
The use of fiber optic cable sensors on water mains has been limited (Higgins and Paulson,
2006). Researchers from Pure Technologies compared the results of acoustic testing (for wire
breaks) of pre-stressed concrete cylinder pipe (PCCP) using fiber optic sensors and more
conventional hydrophone arrays. The fiber optic lines (4 to 8 lines used) measured the strain
energy released from the wire breaks in the PCCP mains. The sensors were tested on 4,700 ft of
a 48-in. PCCP main in Baltimore County, Maryland during the winter of 2005 - 2006. The fiber
optic sensors were found to be accurate to within + 5 ft of the break.
According to USEPA (2009b), there are limitations to using a fiber optic system for corrosion
monitoring in ferrous pipe. These authors assert that "only a small number of locations can be
monitored, and the rate of deterioration is slow and would require years of data collection to
yield any useful data."
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6. Technologies to Evaluate Pipe Bedding and Void Conditions
Pipes may undergo structural failure due to defects in the soil envelope (soil bedding and cover
soil) that supports the pipe. The soil bedding acts as a foundation for the pipe and distributes the
vertical load around the exterior of the pipe wall. Loss of bedding can result in the pipe bridging
areas of reduced bedding or increased voids. This can lead to pipe deflection, pipe deformation,
and longitudinal cracking. There are established and emerging methods to help evaluate the
condition of the pipe bedding and locate voids. Ground-penetrating radar (GPR) is a well-
developed option. Other techniques, such as gamma-gamma logging and infrared thermography,
have been used in other applications and are being studied for their potential use in sewer
condition assessment.
6.1 Ground Penetrating Radar
Description
GPR operates on the same principle as radar by transmitting high-frequency radio waves from an
antenna into the ground (USEPA, 2009a). The waves travel through the ground until they reach
a material with a different conductivity and dielectric constant than the earth. In general, an
object that is harder than the surrounding soil will reflect a stronger signal. Utilities, tunnels, and
other buried objects can therefore be located by transmitting a GPR signal, which is reflected and
recorded by a separate receiving antenna. The amount of time it takes for the electromagnetic
radio waves to be reflected by subsurface features can be analyzed to determine their position
and depth.
GPR is generally used in reflection/scattering mode, as depicted in Figure 6-1 (left side).
Alternatively, GPR can transmit and receive signals between two boreholes, as depicted in
Figure 6-1 (right side).
Figure 6-1. GPR applications in (left) reflection/scattering or (right) trans-illumination mode.
Image from Annan (2003). Reprinted with permission.
Inspection from the Ground Surface
GPR can provide information on the condition of the soil surrounding the pipe, including voids.
Hyun et al. (2007) conducted controlled laboratory experiments to evaluate the potential use of
GPR as a ground-radar-transmitting tool to detect leaks in water pipes. The laboratory scaled-
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down model consisted of a dry sand tank, a pipe, and a simulated zone of leakage adjacent to the
pipe. The size and depth of the pipe, impulse generator, and antennas were scaled to
approximately 1/6 of real world conditions. Results showed that the buried pipe and the effects
of leakage in the soil were clearly identified in the 2-D data plots.
In a review of condition-assessment tools based on new developments and field trials in the U.S.
and UK, Costello et al. (2007) summarized the applications and limitations of GPR. As a ground
surface pipe-locating technique, GPR is independent of the pipe material. As a result, GPR can
locate non-metallic pipes (unlike other pipe location methods that can only detect metallic pipes).
The GPR transmitting unit is most effective when passed perpendicular to the line of the pipe
(Costello et al., 2007). When the pipe's orientation is not known, a grid is laid out on the surface
to ensure complete coverage. The maximum depth of detection is typically about 9.8 ft (3 m)
under favorable conditions.
The use of GPR is limited in several ways (Costello et al., 2007). The pulses lose strength in
conductive materials such as clays and saturated soils, affecting the depth of penetration and the
GPR response. Because GPR does not identify specific utilities (e.g., water or gas pipelines,
electrical or telephone cables), other methods must be used for verification. Finally,
interpretation of GPR data requires highly skilled operators. Research into GPR technologies
has focused on overcoming these drawbacks through antenna design, connections to Computer-
aided Design (CAD) and Geographic Information System (GIS) mapping systems, and the
interpretation of GPR images. For imaging, there are new technologies such as ground
penetrating imaging radar (GPIR) and synthetic-aperture radar (SAR) imaging to present output
in 3-D images.
Makar (1999) described a field test conducted by the National Research Council of Canada at the
Waterline Test Facility in Ottawa to examine the effectiveness of GPR when emitting a signal
from the ground surface. Several test voids were created in the Leda clay soil that occurs
naturally at the test site. Before the beginning of the test, the radar operator was informed of the
number of voids and their approximate locations and the depths of various water lines. The
results showed high levels of false positive and false negative results, which were attributed to
likely interference with the GPR signal by clay soils at the site. Makar (1999) concluded that the
ground surface GPR used at the time of testing would yield unacceptable results in any city with
clayey soils. In another study conducted around the same time, Hunaidi et al. (2000) used a
commercial radar system to collect GPR images of a simulated water leak and concluded that the
method showed promise for initial leak surveys in subsurface environments other than soft,
clayey soil.
Inspection from within the Pipeline
Recently, GPR has been used for in-pipe inspection in conjunction with other inspection
technologies (e.g., digital scanning, CCTV, and ultra-bandwidth). These in-line assessment
methods are generally limited to non-conductive pipe, which allows the signal to propagate
through the pipe wall into the surrounding soil (Sterling et al., 2009). GPR can be operated
remotely as part of a CCTV inspection system using two or three antennas capable of detecting
different frequencies to investigate the structure of the surrounding soil, the interface between the
soil and the pipe, and the structure of the pipe itself. For example, a new remotely operated in-
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line GPR robot, released in May 2010, identifies pipe wall thickness, rebar cover, the
composition of defects, the condition and thickness of pipe liners, and location of cracks for 18
in. to 30 in. non-ferrous pipes (SewerVUE Technology Corp. 2010). "Data collection is
continuous, allowing capturing several miles of data in a few hours. High frequency GPR can
locate targets to a distance of 36-inches..."
GPR was used in combination with sewer scanning and evaluation technology (SSET) to assess
large-diameter PVC-lined concrete pipe in Phoenix, Arizona (Koo and Ariaratnam, 2006;
Ariaratnam and Guercio, 2006). This hybrid technology could "see" through the liner and
evaluate possible voids in the reinforced concrete sewer pipe.
Jaganathan et al. (2009) described a method that uses ultra wideband (UWB) technology to
detect voids in the soil bedding surrounding a pipe. It is expected that this new technology,
when fully developed, will be able to accurately assess the condition of predominantly non-
ferrous buried pipes, including external corrosion, pipe wall thickness, and the presence,
location, orientation, and dimensions of soil voids. Unlike commercially available GPR systems,
the new UWB system uses ultra-short electromagnetic pulses to provide higher resolution and
greater accuracy. The signal produced by the impulse generator is transmitted and received
using two types of UWB antennas. The radar operates in the bandwidth between 3.1 and 10.6
gigahertz (GHz).
Application and Performance in Other Industries
GPR has been widely used for concrete inspection by emitting a signal from the ground surface
to locate underground infrastructure (USEPA, 2009b). It has also been used in military, mining,
archeology, and law-enforcement applications (Makar, 1999). Surface-based surveys using GPR
can provide information about the relative size of a pipe, depending on depth and surrounding
conditions. Determination of material type and other characteristics is generally not possible
with surface-based GPR surveys (Sterling et al., 2009).
6.2 Gamma-Gamma Logging
Description
The gamma-gamma logging (GGL) technique is based on the principle that radioactive gamma
rays, emitted either naturally from the environment or artificially from a shielded industrial
source, are backscattered (and therefore detected) in proportion to the density of the surrounding
material. For most materials, the natural log of the gamma count rate has an approximately
linear relationship to the density of the material (Leibich, 2001; Federal Highway
Administration, 2009a).
The equipment required for GGL consists of a probe containing a small amount of radioactive
material (e.g., cesium-137) that is used as the gamma ray source, and a scintillation detector to
detect the gamma rays. A crystal inside the scintillation detector sends out light pulses when it
receives radiation. The light pulses are converted into an electronic signal that is proportional to
the number of pulses (Ohmart/Vega Corporation, 2010). The probe usually contains two or more
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scintillation detectors, which are shielded from direct radiation by a heavy metal such as lead
(USEPA, 2009a).
GGL has been used to identify and locate cavities in pipe bedding (Eiswirth et al., 2001). Based
on testing in Germany and Australia, researchers have proposed using the GGL technique to
assess the condition of sewers and water lines (Eiswirth et al., 2001). The proposed radiation
probes (i.e., gamma and neutron) would be mounted on a multi-sensor robotic crawler for sewer
condition assessment. Initial laboratory-scale tests have been completed in Germany for the
Sewer Assessment with Multi-Sensors (SAM) system, but this research team has since changed
direction to focus on digital CCTV applications for sewer condition assessment (Burn, Stewart.
Email with author, 2009).
Figure 6-2 illustrates the construction and functional principle of the gamma ray probe and
shows a graph of typical results. The graph shows the counting rate of gamma radiation over
pipe distance (meters). When the probe passes a pipe joint, an orifice, or a cavity in the pipe
bedding, the counting rate changes. The relative sensitivity of the measurement can be increased
by using a lead shield around a portion of the detector (dotted and dashed lines in Figure 6-2).
The solid line in the Figure 6-2 graph represents a more accurate position of pipe anomalies.
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GGL has been thoroughly researched as a geophysical technique and is well established in
mining and petroleum exploration. GGL is used to determine the porosity of the surrounding
material, converted from the measured bulk density (Federal Highway Administration, 2009a,
2009b).
Researchers have tested gamma ray scattering techniques in the characterization of process
pipelines at steel mills (Song et al., 2008). The study used a prototype inspection device
containing cesium-137 to externally inspect the tar deposits in gas pipelines (diameter is 3.5 to
8.5 in. or 90 to 216 mm). The prototype quantified the volume of the tarry deposits to an
accuracy of+ 10%. In contrast, ultrasonic and magnetic inspection methods were not able to
penetrate the dense tarry deposits.
6.3 Infrared Thermography
Description
When a material is heated, infrared radiation flows from warmer to cooler areas. Because
various construction materials have different insulating properties, they retain heat differently
and, therefore, emit different amounts of infrared radiation. Infrared thermography (IRT) uses an
infrared camera to measure infrared radiation across the surface of an object. It produces images
that show areas of differing temperatures in gray tones or colors. Uneven heating or cooling of a
pipe wall or liner can indicate the presence of pipe defects (i.e., variations in pipe wall thickness,
bonding of a liner to the pipe wall, or the presence of soil voids outside the pipe) (Sterling et al.,
2009). Because IRT cannot measure the depth to the pipe, it has limited value for locating pipes
(Costello et al., 2007).
The IRT imaging and analysis system typically includes an infrared sensor and optics head
(similar in appearance to a portable video camera), a real-time microprocessor and display
monitor, data acquisition and analysis equipment, and image recording and retrieving devices.
Equipment is available from several manufacturers. Most non-destructive infrared testing takes
place in the near-infrared region and slightly beyond it in the electromagnetic spectrum, up to
-15 |im (Dingus et al., 2002).
There are two basic IRT methods: passive IRT, which requires no external heat source, and
active IRT, which requires a heat source such as an infrared tube light (USEPA, 2009a). With
passive IRT, the sun serves as the energy source by warming the ground. Conversely, if the test
is performed at night, the ground becomes the heat source and the sky acts as the heat sink.
Active IRT can be used for pipeline assessment when the temperature of the pipes can be
adjusted using a heat source.
When used from the ground surface, IRT has proved to be an accurate and efficient method of
locating subsurface pipeline leaks and voids caused by erosion, deteriorated pipeline insulation,
and poor backfill (Wirahadikusumah et al., 1998). Researchers have found that IRT can also be
deployed inside a sewer and can detect variations in wall thickness, liner bonding, soil voids in
pipe bedding, and leaks. Hunaidi et al. (2000) conducted a field trial to test the applicability of
IRT for detecting leaks in water distribution systems. Thermal trends in infrared images were
conflicting, but the investigators concluded that IRT could be used for leak detection, especially
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as an initial survey tool. Generally, the leak area was seen clearly as a warm spot in
thermographic images. However, several issues were identified for further investigation,
including the effects of ambient conditions (e.g., sky cover, relative humidity), thermal noise
(especially in urban areas), and ground cover.
Maldague (1999) described the use of pulsed active infrared thermography (PAIRT) to detect
thinning pipe walls. The PAIRT technique was demonstrated under laboratory conditions by
focusing an infrared camera on a bent and corroded pipe segment and recording the changing
infrared thermographic images as a function of time. A thermal transient was generated by either
changing the temperature of the circulating water inside the pipe or by heating the external
surface of the pipe with a heat gun. After imposing a thermal gradient, the temperature
distribution and patterns on the outside surface of the pipe were observed using the infrared
camera; abnormal temperature patterns were noted. Maldague (1999) concluded that the high
thermal contrast on the pipe surface and the absence of reflective noise are advantages of this
technique in assessing pipe condition. Sterling et al. (2009) noted that for thick-walled pipe
inspection, prior heating or cooling of the pipe over a period of time may be necessary to get
measurable results. For thin pipe liners in relatively small pipes, differences reportedly can be
observed using a light bulb as a heat source.
Effects of Environmental Factors
Weil (2001) and others (Weigle, 2005; Stockton and Tache, 2006; Costello et al., 2007)
described the influences of environmental factors (e.g., subsurface conditions, type of ground
cover, wind speed) on IRT measurements. Ground cover with a rough surface (e.g., concrete)
can release high amounts of energy, whereas smoother surfaces release less energy. A high-
quality backfill material that is properly placed has the least resistance to conducting energy,
while soil erosion and poor backfill surrounding buried pipelines acts like an insulator (Vavilov
and Burleigh, 2001). In general, the best time for conducting IRT testing is when rapid heating
or cooling of the ground cover surface occurs, and when there is little or no cloud cover. Wind
has a cooling effect on surface temperature. Moisture tends to disperse the surface heat and thus
mask subsurface anomalies.
Application and Performance in Other Industries
IRT has been used to test petroleum transmission pipelines, chemical plants, steam power plants,
and natural gas pipelines (Weil, 2001; USEPA, 2009b; Costello et al., 2007). IRT has also been
used for special building assessments (Tavuk9uoglu et al., 2005; Weil and Rowe, 1998) and
other civil engineering applications (Stimolo, 2003; Maser, 2009).
Astronomers use infrared radiation to investigate the universe. Because it has a longer
wavelength than other forms of radiation, it can pass through clouds of gas and dust and provide
information on distant formations such as stars, planets, galaxies and black holes.
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7. Implementation and Cost Considerations
After the utility has developed a short list of technologies that can address its condition
assessment program objectives, implementation issues should be reviewed to confirm that each
technology is still a viable option. As noted in Chapter 3, the issues include pipe access and staff
training requirements. Cost will also be a key factor in technology selection, and certain site
conditions and pipe characteristics can strongly influence overall project costs. Sections below
present both logistical and cost issues, including costs for various technologies where available.
7.1 Pipe Conditions and Site Access
The common denominator for most of the commercially available condition assessment
technologies is the need for access through manholes. However, access requirements and
required pipe conditions can vary. For example, zoom cameras can be used in areas where
access is tight; in addition to truck mounting, they can be pole-mounted or tripod-mounted to
facilitate access to a site not amenable to using a vehicle-mounted camera. This technology also
has the advantage of not requiring pipe cleaning. However, to get as much coverage as possible,
a zoom camera must be deployed at every manhole, which might be problematic in areas where
manhole access is limited.
Like the zoom camera, electro-scanning (FELL-41, FELL-21) does not require pipe cleaning
before inspection. It does, however, require the pipe to be filled. A sliding plug facilitates this
by allowing small portions of the pipe to be filled at a time. The periods during which high flow
occurs are best for conducting electro-scanning; otherwise supplemental water must be used.
One beneficial strategy is to combine an electro-scanning inspection with pipe cleaning. The
hose used for cleaning can also be used to fill the pipe. Sonar also cannot operate in a dry pipe;
if the pipe is not full, it can only image the portion of the pipe that is under water. A benefit of
this feature is that it can image force mains without taking them out of service. Leak detection
systems also do not require pipes to be taken out of service and can travel extended distances.
The Sahara method remains tethered to the surface access point, but the SmartBall™ is free
swimming and can travel for up to 15 hours, requiring only two access points. This need for
minimal access to the pipe is a clear benefit.
Among the emerging technologies (i.e., those still in the research phase), GGL is relatively
simple to mobilize in current and proposed applications. For sewer condition assessment, it
would be deployed within the pipe mounted on a robotic platform. The probe is small enough to
be easily carried and manipulated by one person, but the gamma ray source may be subject to
special handling requirements of local and federal regulations.
Some technologies do not operate exclusively from the pipe interior. GPR, for example, is
traditionally operated from the ground surface, although it has also been deployed within pipes in
conjunction with SSET. IRT in passive mode is also executed from the ground surface. In
active IRT mode, pipe access is required to adjust the temperature of the pipe.
Some emerging methods pose a more difficult deployment challenge in that inspection must be
executed from the exterior of the pipe. For IE, the equipment must be in direct contact with or
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close to the test material. GWUT also requires direct contact for its operation. As a result, one
section of buried pipe must be excavated and exposed sufficiently so that the transducer can be
attached or placed near the pipe. The distance over which this technology works depends on the
coating, condition, and construction of the pipe as well as the soil conditions. These methods,
which require external access to the pipe, may be limited to special situations where the pipe is
exposed. Therefore, they may not be suitable for system-wide surveys.
7.2 Durability of Equipment
As assessment methods from other industries are emerging for crossover into sewer condition
assessment, their ability to withstand harsh conditions needs to be taken into account. For
example, the durability of the GGL technique is questionable due to the possible mishandling of
the nuclear radiation source. Even though GGL uses a sealed radiation source, there is potential
for the probe to become lodged within the sewer. For example, when the California DOT uses
GGL for acceptance testing of concrete in drilled shafts, the probe was carefully inserted in PVC
inspection tubes. The California DOT first uses a dummy probe to ensure that the probe will not
become lodged in the tube. Similar precautions may be required for inspections of sewers.
Impact echo may also not be robust enough for application in sewer infrastructure assessment
because of its requirement for a clean and dry surface.
GPR and IRT, on the other hand, are relatively durable. GPR has been deployed under harsh
conditions including landmine detection and hazardous waste site investigation. As a result, the
GPR equipment would be exceptionally durable in the typical conditions of the interior of
wastewater collection systems. IRT can be performed using infrared cameras that are protected
from the environment. These cameras have been adapted to many hazardous applications,
including fire fighting.
7.3 Complexity of Training and Data Analysis
Complexity is a measure of the level of training and certification required to execute an
inspection program and evaluate the data. It includes both the labor hours spent in training and
the costs of the training and certification programs. Complexity varies substantially among the
different technologies; greater complexity may limit the ability to use existing in-house resources
to implement an inspection program, which would have a direct impact on cost. Complexity also
is factored into the standardization of a technology. For example, technologies for which there is
an established American Society for Testing and Materials (ASTM) and/or NASSCO standard
have platforms that may be transferable to utilities. Complexity may also affect the ability to
generate useable/repeatable data.
The training to operate camera-based technologies is relatively simple, but training for consistent
classification of defects is more involved. The experience and training of the staff reviewing the
inspection footage is important for providing consistent and reliable inspection results and a
quality condition assessment program. Defect coding systems such as those established by the
Water Research Centre (WRc; http://www.wrcplc.co.uk). NASSCO (PACP; NASSCO, 2001),
and the System Condition & Risk Enhanced Assessment Model (SCREAM™) provide options
for training staff and standardizing condition assessment data. Some utilities have chosen to
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develop their own in-house coding system. Although these standardized coding systems require
training, they would pay off in greater long-term efficiency (see case studies in USEPA, 2010).
Electro-scanning provides immediate results, and the manufacturer of FELL-41 (and FELL-21)
claims that personnel can be trained to operate the unit in a few hours. The output is simply a
graph of changes in current with distance and does not require elaborate processing. Sonar and
laser scanning, however, require post-processing of the data. Although they do not have
standardized coding systems, some skill would be needed to interpret the images produced.
Multi-sensor instruments such as the Cleanflow system, which incorporate high-definition
imaging, sonar, and laser, can entail complex data analysis. Cleanflow produces detailed
reports, including 3-D color-coded images. However, it takes weeks for the data to be processed
by the vendor and the reports to be produced. Data analysis requires a specific skill set, which is
not transferable to utilities. A system that uses standardized software, on the other hand, is more
easily adopted by utilities with some training. In selecting a condition assessment technology,
the utility will need to balance the quality and features of the data acquired with the training and
data processing needs involved.
For GWUT, the inspection requires basic operation skills and a single technician; however, data
processing requires advanced analytical skills (Marlow et al., 2007). For IRT, the greatest
limitation to performing viable infrared surveys of underground fluid lines is the experience and
proficiency of the camera operator (Weigle, 2005).
7.4 Costs of Condition Assessment
Cost is an important factor in the selection of inspection methods. Total cost for the project will
depend upon cleaning required prior to the inspection, costs for field deployment, costs for data
analysis, and site characteristics and access issues. Although the costs associated with location,
setup, and environmental conditions are largely independent of condition assessment
technologies, the amount of equipment and difficulties in moving or setting up certain equipment
will affect the final project costs. The following sections cover general factors likely to influence
cost for all inspection technologies, as well as available cost information for specific
commercially available technologies. Cost information for emerging technologies is not
available, as confirmed in communications with researchers.
7.5 Factors Influencing Cost for Condition Assessment
Apart from the costs associated with a specific technology, certain characteristics of a
wastewater collection system or specific pipe segment influence inspection costs. Location,
project setup, and environmental conditions all affect deployment costs. For example, difficult
site access, high flows, large amounts of debris, and unusually large or small pipes can lead to
higher costs. Equipment type and inspection requirements are also critical factors influencing
the cost of a particular project. Some of the most common "general" cost factors and estimated
costs are summarized in Table 7-1 (Location Cost Factors), Table 7-2 (Project Setup Cost
Factors), and Table 7-3 (Environmental Cost Factors). Many of the "general" cost elements are
calculated on a "per-project," "per-setup," or "hourly" basis depending on the nature of the cost
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factor. Identification and management of cost factors applicable to a particular project can help a
utility anticipate and/or control project cost.
Table 7-1. Site Location Cost Factors
Factor
Distance between
project site and
location of
operator
equipment.
Distance between a
project's
deployment
locations.
Reason
For non-local sites,
operator will incur
and pass on
equipment/
personnel
transportation and
per diem (e.g.
lodging) costs.
Multiple operator
trips (with or without
equipment) across
the project area will
add set-up and
transportation costs.
Cost
$1 to $10 per
mile from
equipment
location to
project site
(round-trip).
$100 to $500
per hour of
intra-project
transportation.
Cost Basis
One time per
project.
Project
duration
(hourly).
Recommendations To
Minimize Additional Cost
Work with qualified operators
near the project site.
Plan projects with the same
operator to minimize multiple
trips.
Send detailed plans to operator
ahead of time so that
deployment locations can be
optimized. Minimize area
required to complete project by
identifying a particular set of
locations and easy access
points.
Table 7-2. Site Setup Cost Factors
Factor
Traffic control or
other security
measures.
Number of
deployment
locations.
Reason
Operator will incur
and pass on traffic
control and security
costs.
The number of
deployment setup
locations affects total
project cost.
Cost
$50 to $500 per
hour on-site for
each site
requiring traffic
control and
security
measures.
Up to $5,000
per setup
location,
depending on
the
technology's
setup
requirements.
Cost Basis
Project
duration
(hourly).
Project
duration (per
setup).
Recommendations To
Minimize Additional Cost
Provide traffic control or
security information to
operator.
Arrange to provide in-house
traffic control/security and
support.
Send detailed plans and
photos to operator or arrange
site visit ahead of time to
optimize deployment
locations.
Minimize area required to
complete project by focusing
on a particular set of locations
and easy access points.
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Factor
Special procedures
required to set up
on site.
Special equipment
or personnel.
Awareness of
locations and
accessibility of
manholes or access
points.
Reason
Operator will incur
costs associated with
special setup. This
includes modifying
or creating non-
standard access
points, river
crossings, flow
diversion, etc.
Examples of non-
standard access
include a pipe
without a manhole
access at the required
location and elevated
manholes.
Special equipment or
personnel required
for a project could
increase its cost.
Contingency costs
may be added if a
utility is known to
have problems with
mapping accuracy or
buried manholes.
Cost
$500 to
$25,000 per
setup,
depending on
work required.
$1,000 to
$100,000 per
project.
Cost estimate
not currently
available.
Cost Basis
Project
duration (per
setup).
One time per
project or
project
duration (per
setup),
depending on
requirements.
One time per
project.
Recommendations To
Minimize Additional Cost
Send detailed plans and
photos to operator or arrange
site visit ahead of time to
identify any additional setup
requirements.
Complete site setups prior to
deployment.
Inform operator ahead of time
and provide in-house
resources when available.
Resolve any uncertainties in
the locations of manholes and
access points and provide
available information to
contractor.
Table 7-3. Environmental Cost Factors
Factor
Impacts of weather
on deployment
procedures.
Reason
Operator may arrive at
project site but be
unable to deploy during
unfavorable weather
conditions, leading to
additional site setup
charges during re-
deployment.
Operator may need to
deploy equipment at
night or may require
flow control prior to
deployment, incurring
additional charges.
Cost
$500 to $5,000
per setup.
Cost Basis
Project
duration (per
setup).
Recommendations To
Minimize Additional Cost
Plan projects during periods
with historically favorable
weather and flow conditions.
For example, if low flow
conditions are needed for
equipment deployment, plan
project for a dry weather period
or nighttime when flows are
typically lower.
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Factor
Unusual site
conditions that pose
health and safety
concerns.
Abnormally high
flows.
High volumes of
sediment, known
structural failures,
or other issues that
would slow progress
through the pipe.
Sewer cleaning
disposal costs.
Reason
Operator may require
special equipment and
procedures to work
safely under atypical
conditions.
Use of equipment may
not be possible, forcing
flow control,
equipment changes, or
other costs.
Individual deployments
may take abnormally
long periods of time,
causing operator to
incur increased costs
(i.e., more labor and
equipment time).
Material accumulated
during cleaning will
require disposal.
Cost
$500 to $5,000
per setup or
$5,000 to
$20,000 per
project.
Up to $5,000
per setup.
$50 to $500 per
hour of
additional
deployment
time.
No cost
estimate
available.
Cost Basis
Project
duration (per
setup or
hourly).
Project
duration (per
setup).
Project
duration (per
hour).
One time per
project (at the
end of the
project).
Recommendations To
Minimize Additional Cost
Ensure operator is aware of
these issues ahead of time.
Provide in-house equipment,
support, or training whenever
feasible.
Make operator aware of flows
ahead of time. Provide detailed
metering or photo information
whenever available.
Control flow and pump stations
prior to deployment to
minimize operator on-site time.
Make operator aware of issues
ahead of time.
Make operator aware of issues
ahead of time.
Project Economy
Inspection costs will also vary depending on the type of work completed as part of the inspection
and how the work is accomplished (contractors vs. utility-owned equipment and in-house staff).
The projects conducted by contractors may cost more (in the near term) than the projects
conducted by in-house staff for utilities that have human resources. In other cases, providing
steady work to a contractor could reduce the project cost. The Denver suburb of Westminster,
CO, for example, has achieved extremely low CCTV inspection costs by providing a private
contractor with steady work (system-wide inspections on a five-year cycle). The city has also
used the findings from CCTV inspections to improve scheduling and prioritization of
maintenance work (Sterling, Raymond. Email with author, 2009).
Projects that have similar unit costs may not yield the same amount of information. A
comparison of zoom camera inspections in Hillsborough County, FL, and Auburn, MA shows
that Hillsborough County had a more cost-effective project (Pryputniewicz, Susan. Email with
author, 2009). Auburn completed a zoom camera inspection of sewer pipes and did a quick
manhole inspection, while Hillsborough County collected global positioning system coordinates
of structures, completed a zoom camera inspection of manholes and sewers, cleaned the sewers,
and then conducted a CCTV inspection for the similar inspection costs reported ($1 to $2 per ft).
When comparing inspection costs for two different studies or systems, it is important to
understand the work completed and the total costs for each case.
Page 7-67
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7.6 CCTV Costs
Although CCTV has been a mainstay of sewer condition assessment for decades, publicly
available CCTV cost data are limited. Two utility surveys containing CCTV cost data were
identified and reviewed. The following section summarizes findings from the surveys conducted
by RedZone (2009) and the Trenchless Technology Center at Louisiana Tech (Simicevic and
Sterling, 2003) independent of this project.
Survey by RedZone
RedZone compiled and analyzed CCTV inspection costs for small-diameter pipes (8- to 12-in.)
at 21 utilities as part of a market research endeavor (RedZone, 2009). Because of the proprietary
nature of the market research project, only generalizations can be drawn from the study. An
obvious observation is the considerable variability in CCTV inspection costs, from $0.28 to more
than $1.00 per ft.
Table 7-4 summarizes the average inspection costs and project size (i.e., length of pipe
inspected) for small, medium, and large utilities surveyed. The average costs are generally
higher for smaller utilities. The costs among the small utilities are skewed upward by one
unusually high value ($5.01 per ft). When this outlier is removed, the average cost for the small
utilities is $0.84 + $0.37 per ft, which still exceeds the average cost for medium and large
utilities.
RedZone identifies other factors that affect inspection costs, including prevailing regional wages
and the use of outside contractors rather than utility-owned equipment and in-house staff. For
example, the northeastern U.S. has higher labor rates and thus higher CCTV inspection costs.
Average costs are higher for utilities that outsource inspections ($1.19 + $1.25 per ft) than for
those that perform inspections in-house ($0.64 + $0.35 per ft). Most of the small utilities in the
RedZone study outsourced inspections, which may partially explain the higher costs.
Table 7-4. CCTV Inspection Costs from Market Research Study
Utility Size
(n=sample size)
Small (n=8)
Medium (n=8)
Large (n=4)
Average Cost per ft +
Standard Deviation
$0.84 +_$0.37
$0.62 + $0.29
$0.76 + $0.44
Range of Cost per ft
$0.35 to $1.47
$0.28 to $1.21
$0.33 to $1.17
Average Length of Sewer
Pipe Inspected + Standard
Deviation (ft)
513,755+160,293
1,370,572 + 377,091
5,586,947 + 3,657,579
Data from RedZone (2009).
Survey by Trenchless Technology Center (TTC) at Louisiana Tech
Simicevic and Sterling (2003) compiled 310 bid tabs or bidding summaries from 67
municipalities in 39 states that sought to contract for sewer pipe rehabilitation by various
trenchless technology methods. More than 100 of the bid documents - representing 19
municipalities in 17 states - received by TTC included costs for CCTV inspection of main lines.
Page 7-68
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As shown in Figure 7-1, average CCTV inspection costs on the basis of geography exhibit a
fairly wide range. Average costs in two localities (Long Island City, NY, and San Antonio, TX)
were particularly high; however, no explanations were provided in the report. Plotting the linear
footage of pipes inspected and the average inspection cost yields a generally inverse relationship
between project size and average per-unit cost. In general, bid prices for larger projects (i.e.,
more footage) are associated with low per-unit inspection costs (Figure 7-2). Furthermore,
although the range of costs was large, over 50% of the bid prices were at $2.00 per ft or less, as
shown in the histogram in Figure 7-3. The costs reported by Simicevic and Sterling (2003) are
generally higher than those compiled and reported later by RedZone (2009). This may be partly
due to the sizes of the projects; the linear footages in the RedZone data were much greater than
the data from the Simicevic and Sterling report because the latter were associated with
rehabilitation projects and were not full system inspections.
Average Bid Price by Municipality
$14
i $12
s $10
2 $8
£ $6
2 $4 i]
? $2 n i I
* <;o M N
2 -?u
o -c
| |
'ob
tH
o
o
(0
J
Ii
LO
I San Antonio (2
tH
O
O
if
Figure 7-1. Average bid price ($ per linear ft) for CCTV inspection of pipelines in various U.S.
municipalities (number of bids).
Data from Simicevic and Sterling (2003).
Page 7-69
-------
Bid Price vs. Length of Pipe Inspected
O)
u
00
$18.00
$16.00
$14.00
$12.00
$10.00
$8.00
$6.00
$4.00
$2.00
$0.00
5000 10000 15000 20000 25000 30000 35000
Length of Pipe (ft.)
Figure 7-2. CCTV inspection bid prices for projects of various lengths.
Data from Simicevic and Sterling (2003).
I/)
13
CO
'o
E
3
z
40
35
30
25
20
15
10
5
0
Number of Bids vs. Unit CCTV Inspection Cost
i 1
i i
i j
|| • • : , - : : —
1 ! ' i D Q :- j ' '
$1 $2 $3 $4 $5 $6 $7 $8 $9 $10 $11 $12 $13 >$13
Bid Price ($/LF)
Figure 7-3. Distribution of bid prices for CCTV inspection.
Data from Simicevic and Sterling (2003).
7.7 Cost of Other Technologies
Cost of Digital Scanning
Available cost data for digital scanning are limited. In addition to evaluating the performance of
the early version of the SSET system, CERF (2001) performed a comparative cost analysis of the
inspection of 22,000 mi. of pipe in 13 municipalities. The cost of digital scanning with the SSET
system was conservatively estimated at $3.00 per ft. This estimate is about 50% higher than the
Page 7-70
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costs for CCTV inspections with sewer line cleaning and 75% higher than CCTV inspections
without sewer line cleaning. The report noted that SSET might be economically attractive to
utilities that have very high CCTV costs. In their comparison of CCTV and digital scanning in
Wuppertal, Germany, Stein and Brauer (2004) reported that the ARGUS 4 CCTV system cost
approximately $0.38 per ft, while the PANORAMO system (including data post-processing) cost
approximately $0.24 per ft.
Zoom Camera Costs
A number of case studies point out the benefits of using zoom cameras to achieve savings for
utilities. According to Rinner and Pryputniewicz (undated) and Joseph and DiTullio (2003),
zoom camera surveys are one-half to one-third of the cost of cleaning sewer lines and conducting
CCTV inspections. The town of Auburn, Massachusetts, saved about $50,000 by inspecting
60,000 ft of sewer pipes with zoom cameras instead of performing CCTV inspections (Rinner
and Pryputniewicz, undated). Lee (2005) reported that a mid-Atlantic utility spent $90,000 for
zoom camera inspection of 41,000 ft of interceptors. In-line CCTV inspection for the same
system, including cleaning and flow control, would cost about $750,000.
Zoom camera inspection has the disadvantage in not detecting problems with lateral connections
(other than those that protrude into the main line). This shortcoming may render the technology
inappropriate for some inspection purposes (e.g., inspection of laterals and lateral connections).
However, if the primary objective is to inspect interceptors and mains, use of zoom camera for
inspection is a cost-effective alternative.
Cost of Electro-Scanning
Few data are available on the cost of electro-scanning. Moy et al. (2006) indicated that the
estimated cost of electro-scanning is $15,000 per event, compared to an anticipated $100,000 per
event to clean and inspect the pipe twice (during design and then prior to rehabilitation) using
CCTV. Similarly, Harris and Dobson (2006) found that electro-scanning was 3 to 4 times less
expensive than CCTV and JPT. One factor contributing to the lower electro-scanning costs is
the low cost to train field crew as they are not required to analyze the captured data. Data
analysis is typically performed in the office following the field operation.
Page 7-71
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8. Conclusions and Future Research Needs
For decades, utilities have used conventional CCTV to identify defects and obtain a record of
their wastewater collection systems' conditions. A number of newer technologies, however, are
now either commercially available or being researched for adaptation to sewer condition
assessment. Some of these newer technologies are camera-based (zoom camera, digital
scanning) like CCTV, but others are based on different principles and provide information
complementary to that obtained by CCTV. This expanded list of sewer condition assessment
technologies offers utilities new options for designing condition assessment programs that meet
their objectives (e.g., rapid screening, in-depth assessment, evaluation of pipe wall integrity).
In gathering the information for this report, research needs have become apparent:
• There is an ongoing need for evaluations of technology performance. Because most
available information on sewer condition assessment comes from technology vendors and
operators, the successes of the methods tend to be highlighted. A comprehensive third-
party survey is needed to compile and analyze utility experiences with sewer inspection
technologies, including their performance and cost. Systematic testing of promising
technologies is also needed.
• Comprehensive cost data are not available for all technologies, and where available,
they can vary widely. For example, according to the studies cited in this report, CCTV
costs vary greatly depending on such factors as local labor rates and size of project.
Cost/benefit analyses performed in support of a planned sewer inspection and condition
assessment program will be affected by local rates for CCTV inspections and for any
newer or alternative technologies under consideration. As new technologies mature, the
costs tend to decrease. Hence, cost data presented for innovative technologies represent a
snapshot that may be useful for comparative purposes but may not be indicative of future
costs. The information presented in this report also outlines some of the site- and project-
specific factors influencing the inspection costs. Because of the variety of factors
involved, "generic" costs cannot be provided for each technology. However, an
understanding of the factors that influence pricing may help utilities anticipate the
relative cost of a condition assessment program.
Sewer condition assessment technologies can be loosely divided into the "visual" (i.e., camera-
based) technologies (CCTV, zoom camera and digital scanning) and the "quantitative"
technologies (electro-scanning, laser, sonar, acoustic, GPR, and other innovative methods).
Zoom cameras offer greater production rates than CCTV and can serve as a screening and
prioritization tool. Uncertainties surrounding zoom cameras' performance involve effective
sight distance and the detection of defects away from the inspection manhole. Digital scanning
provides detailed and high-quality images and allows post-processing of data; but from the
limited available cost data, digital scanning is more expensive than zoom cameras and CCTV.
Given the long history and value associated with visual inspection, it is likely that camera-based
methods will remain in the forefront of inspection and assessment programs. Additional
performance and cost data will help utilities decide which newer visual method is better for their
needs.
Page 8-72
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Quantitative technologies provide very different types of information than camera-based
technologies, allowing better elucidation of pipe geometry, sediment accumulation, thinning of
pipes due to corrosion, joint defects, and I/I. It is challenging to compare condition assessment
information provided by electro-scanning, laser, sonar, or acoustic methods directly with
information from camera-based inspections. Comparisons that have been made (e.g., electro-
scanning compared to CCTV) underscore the fact that different technologies may detect different
numbers and types of defects in a pipe. The available performance information indicates that
visual and quantitative technologies can be complementary and may be best used in concert to
meet utilities' needs.
Municipalities will benefit from continued research on the performance of the various
quantitative technologies as compared to CCTV inspection. A field demonstration program
planned as part of this project is one such research effort. The purpose of the field demonstration
is to collect cost and performance data that will help wastewater utilities select the most
appropriate condition assessment technologies for their wastewater collection systems. The field
demonstration will be conducted in Kansas City, Mo. in the summer of 2010. Four condition-
assessment technologies are selected for testing in addition to a baseline CCTV inspection:
digital scanning, zoom camera, electro-scanning, and 2-D laser. The field demonstration
methods and findings will be presented in a separate report.
A number of technologies currently used in other fields have been identified as having a strong
potential for transfer to sewer condition assessment. These "crossover" technologies (e.g.,
gamma-gamma logging, infrared thermography, impact echo - spectral analysis of surface
waves, and micro-deflection) will be appropriate primarily for inspecting pipe wall integrity and
pipe bedding. One technology - ground-penetrating radar - is already commercially available
and allows evaluation of the soil envelope surrounding the pipe. When these innovative
technologies become commercially available and cost-effective for sewer condition assessment,
utilities will have many additional options to assess the conditions of their wastewater collection
systems.
Page 8-73
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Page 9-79
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Appendix A: Technology Fact Sheets
Page A-83
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Fact Sheet on CCTV Camera Inspection Technology
Description
Innovative
Features
Vendors
Research
Questions
Current
Applications
Limitations
Vendor
Claims
Pipe Type
Pipe Material
Pipe Diameter
Flow Regime
Preparation
CCTV technology uses a video camera with lighting to provide a visual recording of
the interior pipeline condition. Cameras are deployed using mobile robots called
crawlers or tractors and can also be mounted to float rigs for inspecting larger diameter
pipe. The ability to pan, tilt, and zoom allows the operator to gain a full
circumferential view of the pipe that is partially filled with water.
• Digital CCTV cameras produce high-resolution images.
• LED lighting combined with a digital CCTV camera provides image quality
adequate for assessing wall condition in large-diameter pipe.
• Digital CCTV vehicles equipped with fiber optic cabling can inspect 10,000 ft of
sewer at a time compared to 2,000 ft for analog CCTV cameras.
• New cameras are smaller, more robust and less expensive.
There are numerous vendors of CCTV cameras.
• What is the most effective way to use historical CCTV records?
• How can CCTV data be integrated with other historical system data, inspection
records etc. to form a baseline of system condition?
• Primary method for comprehensive inspection of gravity sewers and service
laterals.
• Documents location of leaks, service laterals and sediment/debris levels.
• Used in combination with laser and sonar to provide full circumferential view of
interior pipe conditions.
• Standard CCTV inspection is used as a benchmark or baseline for comparing
inspection data from other condition assessment technologies.
• CCTV can only provide a visual representation of the interior pipe surfaces above
the waterline; it does not provide any quantitative data on pipe wall structure,
degree of corrosion, or sediment depth.
• Analog CCTV cameras do not provide a high-resolution image.
• It does not provide quantitative data to determine variations in sewer dimensions,
subtle deformations, or debris level, and does not provide a view of the soil
envelope supporting the pipe.
• The quality of defect identification and pipe condition assessment is highly
dependent on operator interpretation and skill level, on picture quality, and on
flow level.
• CCTV inspection is hindered by varying pipe diameters, materials (including
brick, concrete, ductile iron, and clay), odd shapes, sumps, and angle entries.
• There are needs for higher resolution cameras with better lighting; and
improvements in crawler technology to better negotiate obstructions, grease, and
off-set joints.
• Inspection distance, line resolution, inspection reporting software, portability.
• Waterproof housing designed for sewer environment.
• Rotating head with 360° viewing angle.
Gravity sewers. Push cameras are used in service laterals.
No restrictions; Applicable for any pipe material.
>6 in. (push cameras can inspect 1 in. - 12 in.)
Lower flow conditions will provide more pipe surface area for inspection.
Sewer cleaning may be required prior to inspection.
Page A-84
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Fact Sheet on Digital Scanning Technology
Description
Innovative
Features
Limitations
Potential Vendors
Research
Questions
Typical
Applications
Status
Vendor Claims
Pipe Type
Pipe Material
Pipe Diameter
Flow Regime
Preparation
Digital scanning uses one or two high-resolution digital cameras equipped with
wide-angle lenses to generate two types of images: an "unfolded" view of the
sides of the pipe, and a circular view down the pipe. Information from the two
cameras can be combined to form 360-degree spherical images. Digital
scanners are transported using self-propelled crawlers. Data are typically
transmitted to a surface viewing station where they can be viewed in real-time
or recorded for later evaluation.
• The unfolded view enhances computer-aided measurement of defects and
objects.
• Digital measurements of defects allow direct comparison from one
inspection to the next.
• Post-processing software enables the analyst to identify defects and define
their magnitude.
• Increased quality assurance and quality control of data imagery.
• More costly and lower production rate compared to traditional CCTV.
• Only identifies defects above water line.
Product(s) Vendor URL
DigiSewer Envirosight, LLC http://www.envirosight.com
Panoramo Rapidview-IBAK http://www.rapidview.com
USA
Cleanflow/Fly CUES Inc. http://www.cuesinc.com
Eye
• Is digital scanning more cost-effective in terms of total production rate
than CCTV?
• How does the quality of data compare to that produced by "conventional
CCTV inspection" (defined as a CCTV inspection in compliance with
NASSCO standards)?
• Does post-processing of data enhance the quality of condition assessment
information?
• Are vendor claims regarding inspection rate and camera resolution valid?
• Measure pipe grade, ovaliry and deflection.
• Detect and measure cracks, leaks, root intrusion, overall condition of pipe.
Commercially available; technology enhancements under development.
1. Inspection Rate: According to vendors, the inspection rate for both Panoramo
and DigiSewer is 70 fpm.
2. Applicable Pipe Size: The Panoramo system literature claims adequate
camera resolution for inspection of up to 80-in. diameter, while DigiSewer
literature states an upper diameter of 60-in.
3. Image Quality: In general, vendors report that the digital scan image quality
is superior to conventional CCTV image data.
Gravity sewers. Limited applicability for force mains and service laterals.
No restrictions; Applicable for any pipe material.
6-in. to 72-in. depending on equipment model and pipe conditions.
Dry pipe or during periods of low flow.
Pipe must be cleaned prior to inspection.
Page A-85
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Fact Sheet on Laser Scan Technology
Description
Innovative
Features
Limitations
Vendors
Research
Questions
Typical
Applications
Vendor
Claims
Pipe Type
Pipe Material
Pipe Diameter
Flow Regime
Preparation
Laser scanning generates a cross-sectional profile of a pipe's interior wall. The
common 2-D technique uses a laser to create a line of light around the pipe wall that is
typically observed via an onboard camera. The laser light highlights the shape of the
sewer, allowing for the detection of changes to the pipe's shape, which may be caused
by deformation, corrosion, or siltation. The 3-D technique employs multiple points
measured individually to create a 3-D model of the pipe wall. A 2-D cross-section can
be extracted from the 3-D model.
Generates precise models of pipe surfaces that reveal minor surface abnormalities.
Provides geometric information about the pipe interior that is different from and
complementary to CCTV data.
Laser inspection can only be used to inspect dry
entire internal surface of a pipeline requires the
Product
Active 3-D Laser
Scanning
Coolvision
Laser Profiler
Laser Profiling Tool
Cleanflow
Laser Profiler
Vendor
Redzone Robotics
Sima
Environmental
CUES IMX
Envirosight
Hydromax
R&R Visual, Inc.
portions of a pipe. Assessment of the
pipe to be taken out of service.
http://www.redzone.com
http : //www . simaenvironmental . com
http://www.cuesinc.com
http://www.envirosight.com
http://www.hvdromaxusa.com
http://www.expipeinspection.com
• In terms of technical performance and cost, what are the differences between 3-D
and 2-D laser profiling?
• Does the added cost of the laser profile produce definable, tangible benefits in
terms of enhanced condition assessment information?
• Measure pipe grade, ovaliry and deflection.
• Detect and measure cracks, corrosion, sediment depth, water depth, and service
locations.
• Verify the installation of new pipe or pipe liner and identify any necessary
remedial actions.
• Can create accurate 2-D or 3D models of pipes.
• Can measure characteristics such as pipe ovaliry, capacity, grade and deflection,
sediment depth and volume, water depth, and cracks.
Gravity sewers, force mains.
No restrictions. Applicable for any pipe material.
24-in. to 60-in. (typical application); 4-in. to 160-in. (full range).
Dry pipe or during periods
Pipe must be cleaned prior
manhole. Previous CCTV
condition.
of low flow.
to inspection. Minimum 24-in. diameter for deployment in
inspection records should be reviewed to understand pipe
Page A-86
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Fact Sheet on Sonar Technology
Description
Innovative
Features
Limitations
Potential
Vendors
Research
Questions
Vendor Claims
Pipe Type
Pipe Material
Pipe Diameter
Flow Regime
Preparation
Sonar/ultrasonic inspections of pipelines are accomplished by passing a sonar head
through the pipe being inspected. Depending on the size and flow conditions of a
pipe, the sonar head is deployed into the pipeline on a raft, skid, or robotic tractor.
As the sonar head moves through the pipeline, it sends out high-frequency
ultrasonic signals, which are reflected by the pipe walls and then received by the
sonar head. The reflection of the signals changes when there is a change in the
material reflecting the signal, allowing for the detection of defects. The time
between signal transmission and receipt can be used to determine the distance
between the sonar head and the pipe wall, as well as to determine the internal
profile of the pipe.
Sonar is capable of inspecting pipes below the water surface. The technology does
not require bypass pumping or pipe cleaning.
Sonar is currently not applicable to pipe surfaces above the water line. Current
research is evaluating new sonar devices to address this issue.
There are numerous manufacturers of sonar equipment.
• Can sonar technology map defects (i.e. pipe wall loss, ovality) in the invert as
effectively as it can quantify sediment accumulation?
• Does the usage of sonar in combination with laser or digital scanning provide
an assessment of the full pipe circumference?
• Can data interpolation of sonar be standardized?
• Results in a detailed profile of the pipe wall below the water surface, in both
full and partially full pipes.
• Detects defects greater in than 1/8-in. in size, including pits, cracks,
corrosion, and debris accumulation.
Gravity sewers, force mains.
No restrictions. Applicable for any pipe material.
>2-in.
A minimum water depth is required to submerge the head of the sonar unit. See
manufacturer's guidelines.
Pipe cleaning is not required prior to inspection. Previous CCTV inspection
records should be reviewed to understand pipe condition.
Page A-87
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Fact Sheet on Zoom Camera Technology
Description
Innovative
Features
Limitations
Current
Applications
Status
Vendors
Research
Questions
Vendor Claims
Pipe Type
Pipe Material
Pipe Diameter
Flow Regime
Preparation
Zoom camera inspection involves the generation of still imagery or recorded video
imagery of the pipe interior using a stationary camera mount. The camera equipment
does not pass through the entire length of the pipe segment(s); instead, the camera is
truck- or pole-mounted and lowered into a manhole to perform the inspection.
Newer zoom cameras can pan 360 degrees and zoom farther down pipes. Some
cameras have inter-changeable camera heads with different zoom capabilities.
The effectiveness of zoom cameras is limited by sight distance, the distance from
which a defect remains visible. Limitations in sight distance make it difficult to
complete inspections from manhole to manhole, and may prevent identification of
significant defects.
• Detect and measure cracks, leaks, root intrusion, overall surface condition of
pipe/manholes.
• Typically used as a screening tool to identify and prioritize gravity sewers for
more detailed CCTV inspection, cleaning and/or maintenance.
Commercially available.
Product
Aqua Zoom
Aries HC3000 Zoom
Pole Camera
QuickView
Everest Ca-Zoom PTZ
CUES IMX Truck-
Mounted Zoom
Camera
PortaZoom
Vendor
AquaData, Inc.
Aries Industries
Envirosight, LLC
GE Sensing &
Inspection
Technologies
CUES IMX
CTZoom Technologies
http://www.aquadata.com
http://www.ariesind.com
http : //www . envirosight. com
http : //www . ge inspection
technologies.com
http : //www . cue sine . com
http://www.ctzoom.com
• How much does the limited sight distance of this technology inhibit its use in
condition assessment?
• How does the quality of data compare to that produced by conventional CCTV
inspection?
• Is zoom camera a cost-effective tool for prioritizing inspections?
• Can the term "sight distance" be standardized?
• How do the inspection rate and inspection distance compare to vendor claims?
• Higher production rate than conventional CCTV inspection.
• Lower inspection cost as compared to CCTV.
• Sight distance for specific pipe diameters (Note: these claims should be verified
with field data).
Gravity sewers.
No restrictions. Applicable for any pipe material.
>6-in.
Dry pipe or during periods of low flow.
None required.
Page A-88
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Fact Sheet on Focused Electrode Leak Location (FELL) Technology
Description
Innovative
Features
Limitations
Potential
Vendors
Research
Questions
Current
Applications
Vendor
Claims
Pipe Type
Pipe Material
Pipe
Diameter
Flow Regime
Preparation
FELL locates pipeline leaks and identifies their magnitude using the electro-scan
method in accordance with ASTM Standard F2550-06. The electro-scan test is carried
out by applying an electrical potential between an electrode in the electrically non-
conductive pipe and an electrode on the ground surface. A sliding pipe plug prevents
the current from traveling along the pipe's interior walls and maintains hydraulic
surcharge conditions. The pipe wall has a high electrical resistance, preventing the flow
of current to the ground surface unless there is a pipe defect.
FELL technology provides a quantitative measure of leak potential without relying on
visual observation and interpretation of pipe defects and external conditions that are
temporal in nature (e.g., seasonal, wet weather dependent). Pipe defects are coded
automatically by the accompanying software.
Drawbacks include the inability to determine the cause of a pipe defect (e.g., roots,
misaligned joints, crown corrosion) or the defect's position along the pipe
circumference.
Product
FELL-41
New (pending
specifications from
vendor)
QuickView
Vendor
Burgess & Niple
Leak Busters Inc.
Envirosight, LLC
http : //www . aquadata. com
http://www.ariesind.com
http://www.envirosight.com
• Can leak potential be interpreted qualitatively for use in defect coding?
• Can leak potential be correlated to defect magnitude?
• Can the electrical current data distinguish among types of defects?
• How does information on pipe defects based on FELL inspection compare to
information generated from conventional CCTV inspection?
Inspection of main lines and laterals.
The manufacturer claims that the technology locates defects within inches, detects any
leak type, determines size of defects, quantifies leakage rate on active and inactive
leaks, produces reliable and repeatable results, uses a production rate of 3,000 to 4,000
ft/day), and provides results independent of ground conditions.
Gravity sewers, force mains, and service laterals.
Non-conductive, non-ferrous pipe materials including PVC, VCP, RCP, or in ferrous
pipe lined with cementitious mortar.
3 -in. to 60-in.
The pipe upstream of the sliding plug should be fully surcharged. A nearby source of
water is necessary because the time required to let the pipe fill would otherwise be
excessive.
Debris must be removed to allow the sonde (i.e., probe) to traverse the pipe, but
complete sewer cleaning and vehicle access are not required.
Page A-89
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Fact Sheet on Leak Detection Systems
Description
Innovative
Features
Vendors
Research
Questions
Typical
Applications
Limitations
Vendor
Claims
Pipe Type
Pipe Material
Pipe Diameter
Flow Regime
Preparation
Leak detectors are devices used to detect the sound or vibration produced by leaks in
pressurized waterlines or in sewers. In-line leak detectors are a more recent
advancement in the use of acoustic technology for condition assessment of pipes. They
are deployed in a pipeline to continuously monitor leakage.
• Can detect very small leaks.
Product(s)
Sahara® Leak
Detection
System
Smartball®
Leak Detector
Vendor
Pressure Pipe
Inspection Company
Pure Technologies
http://www.ppic.com
http://www.puretechnologiesltd.com
• How can equipment deployment be improved at low water velocities (<3 fps)?
• How does the technical performance and cost of available technologies compare
in third party investigations?
• How accurate is leak measurement at line pressures >20 psi under simulated or
field conditions?
• Leak detection in pressurized water lines.
• Leak and gas pocket detection in wastewater force mains.
• The Sahara® system requires a minimum water velocity of 3 fps to ensure the
device can move through the pipe and requires a system pressure between 10 and
150 psi for the system to recognize leaks.
• The Smartball® sensor requires a minimum water velocity of 1.64 ft/sec.
• The Sahara® system can detect leaks as slow as approximately 0.25 gallons/hour.
• The Sahara® system can locate leaks within 2 feet.
• As the Smartball® passes through the pipe, its progress can be tracked, allowing
for leak location to be determined within one meter of accuracy.
• The Smartball® can operate and store data for up to twelve hours before it is
retrieved.
Wastewater force mains.
No restrictions; applicable for any pipe material.
>4-in. (Sahara®); >10-in. (Smartball®).
Requires minimum flow to be carried through the pipe.
Sewer cleaning may be required prior to inspection.
Page A-90
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Fact Sheet on Acoustic Monitoring Systems
Description
Innovative
Features
Limitations
Vendors
Research
Questions
Typical
Applications
Status
Vendor Claims
Pipe Type
Pipe Material
Pipe Diameter
Flow Regime
Preparation
Acoustic monitoring systems are installed along pre-stressed concrete
cylinder pipe (PCCP) to provide continuous monitoring of the general
condition of the pipe. The systems work by detecting the acoustic signal
produced by breaking or broken pre-stressed wire within pipes. General
distress in the pipeline is characterized by the frequency and number of
wire breaks, or wire-related events, over a period of time. While the
systems do not identify individual defects, they are useful as screening
techniques to determine if further condition assessment should be
performed.
• Some systems work while pipelines are fully operational.
• All systems provide advanced warning of pipe failure.
• The SoundPrint® AFO system uses acoustic fiber-optic cable for detecting
acoustic signals. The sensor does not contain any electronics, therefore
there is little to no background noise created by the device.
• Only detects general distress in the pipeline, not individual defects.
• SoundPrint® AFO system can only be installed when the pipeline is taken
out of service and dewatered.
Product(s)
Soundprint®
Acoustic
Monitoring
System
Acoustic
Emission
Testing (AET)
System
Vendor
Pure Technologies
Pressure Pipe
Inspection Company
URL
http://www.puretechnologiesltd.com
http://www.ppic.com
• How does technical performance and cost of available technologies
compare in third party investigations?
• PCCP sewage force mains.
Commercially available.
The SoundPrint®
pipeline from one
acoustic fiber optic sensors can monitor up to 15 miles of
insertion point.
Wastewater force mains.
PCCP.
>18-in.
No limits.
None.
Page A-91
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Fact Sheet on Ground Penetrating Radar (GPR)
Description
Innovative
Features
Limitations
Vendors
Research
Questions
Typical
Applications
Status
Pipe Type
Pipe Material
Pipe Diameter
Flow Regime
Preparation
GPR operates on the same principle as radar. A transmitting antenna emits
high-frequency radio waves into the ground. The waves travel through the
ground until they reach a material that has a different conductivity and dielectric
constant than the earth. The signal is reflected and recorded by a separate
receiving antenna. The return time can be analyzed to determine the position
and depth of features below the ground surface. Since GPR can detect
underground voids, it is potentially useful for examining pipe bedding; and
since saturated soil slows radio waves, GPR can also potentially be used to
locate leaks. Research into using GPR for sewer and bedding condition
inspections is ongoing.
Recently, GPR has been deployed with the digital scanning and ultra-bandwidth
technologies on an inspection robot inside a pipeline to assess its condition.
New technologies such as ground penetrating imaging radar and synthetic-
aperture radar imaging have improved the presentation of output with 3-D
images.
GPR does not identify specific utilities (e.g., water, gas, telephone, electric), so
verification is necessary. GPR is unlikely to be feasible for ferrous force mains.
The pulses lose strength in conductive materials, such as clays and saturated
soils, thereby affecting the depth of penetration and the GPR response.
Interpretation of GPR data requires highly skilled operators.
Product(s) Vendor
Surveyor SewerVUE http://www.sewervue.com
• How will in-line GPR perform in assessing pipeline bedding under controlled
conditions?
• What other defects/characteristics can GPR detect in pipeline inspections?
• Current research is focused on overcoming current drawbacks (e.g., pulse strength
in conductive materials) through antenna design, connections to CAD and GIS
mapping systems, and the interpretation of GPR images.
• Location of underground tunnels, mines, concrete structures and voids.
• In-line assessment of non-conductive pipe.
• Rapid reconnaissance survey tool for leak management.
• Commercial GPR systems are available for locating underground utilities but
have not been used for pipeline inspections.
• GPR systems for internal pipe inspection are in the prototype stage.
Any.
Concrete, asbestos cement, plastic, brick.
Any.
No limits.
Unknown.
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