Lessons
Learned
NaturalGas
EPA POLLUTION PREVENTER
£XX4
From Natural Gas STAR Partners
DIRECTED INSPECTION AND MAINTENANCE AT GATE STATIONS
AND SURFACE FACILITIES
Executive Summary
In 2001, fugitive methane emissions from gate stations and surface facilities in the United States totaled about 27
million cubic feet (MMcf) from leaking meters and regulating equipment. Implementing a directed inspection and
maintenance (DI&M) program is a proven, cost-effective way to detect, measure, prioritize, and repair equipment
leaks to reduce methane emissions.
A DI&M program begins with a baseline survey to identify and quantify leaks. Repairs that are cost-effective to fix
are then made to the leaking components. Subsequent surveys are based on data from previous surveys, allow-
ing operators to concentrate on the components that are most likely to leak and are profitable to repair. This
Lessons Learned study focuses on maximizing the savings that can be achieved by implementing DI&M pro-
grams at gate stations and surface facilities.
Natural Gas STAR distribution partners have reported significant savings and methane emissions reductions by
implementing DI&M. Based on partner data, implementing DI&M at gate stations and surface facilities can result
in gas savings worth up to $1,800 per year, at a cost of between $20 and $1,200.
g
•a
Leak Source
Gate Station
and Surface
Facility
Equipment
Annual Volume of Gas
Gas Lost(Mcf/site)
0 to 600
(typical estimates for
leaking facilities is
30 to 200)
Method for
Reducing Loss
Locating and
repairing leaks.
Value of Gas
Saved1 per site
Up to $1,800
Total Cost to Find
and Fix Leaks
$20 to more than
$1,200
(varies depending on
facility size and types
of repairs)
Annual Partner
Savings
$50 to more
than $1 ,000
(varies depending
on survey costs,
leak rates, number
of sites)
1Gas valued at $3 per Mcf.
This is one of a series of Lessons Learned Summaries developed by EPA in cooperation with the natural gas industry on superior
applications of Natural Gas STAR Program Best Management Practices (BMPs) and Partner Reported Opportunities (PROs).
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Introduction
Technology
Background
Gate stations (or 'city gates') are metering and pressure regulating facilities
located at the custody transfer points where natural gas is delivered from trans-
mission pipelines into the high-pressure lines of a local distribution company.
Gate stations typically contain metering runs as well as pressure regulators,
which reduce the transmission line pressure from several hundred pounds per
square inch gauge (psig) to a suitable pressure for the distribution system (usu-
ally less than 300 psig). Other surface facilities within a distribution system
include heaters to replace the heat lost from gas expansion, and downstream
pressure regulators, which further reduce gas pressure so that gas can be
delivered safely to customers. Exhibit 1 is a schematic illustration of a gas distri-
bution system showing a gate station and pressure regulating facilities.
Exhibit 1: Distribution System Schematic Showing Gate Station and
Pressure Regulators
Services
Gate Station
Pressure Regulator
Stations
Mains
Transmission
Pipeline
Customer
Meters
Gate stations and surface facilities contain equipment components such as
pipes, valves, flanges, fittings, open-ended lines, meters, and pneumatic
controllers to monitor and control gas flow. Over time, these components
can develop leaks in response to temperature fluctuations, pressure, corro-
sion and wear. In general, the size of the facility and the facility leak rate cor-
respond to the inlet or upstream gas pressure; the higher the inlet pressure,
the larger the gate station and the greater the number of equipment compo-
nents that may develop leaks.
DI&M is a cost-effective way to reduce natural gas losses from equipment
leaks. A DI&M program begins with a comprehensive baseline survey of all
the gate stations and surface facilities in the distribution system. Operators
identify, measure, and evaluate all leaking components and use the results to
direct subsequent inspection and maintenance efforts.
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The following sections describe various leak screening and measurement
techniques that can be cost-effective at gate stations and pressure regulat-
ing facilities. The appropriateness of the various screening and measurement
techniques will depend upon the configuration and operating characteristics
of individual distribution system facilities.
Leak Screening Techniques
Leak screening in a DI&M program may include all components in a com-
prehensive baseline survey, or may be focused only on the components that
are likely to develop significant leaks. Several leak screening techniques can
be used:
* Soap Bubble Screening is a fast, easy, and very low-cost leak screen-
ing technique. Soap bubble screening involves spraying a soap solution
on small, accessible components such as threaded connections.
Soaping is effective for locating loose fittings and connections, which
can be tightened on the spot to fix the leak, and for quickly checking the
tightness of a repair. Operators can screen about 100 components per
hour by soaping.
* Electronic Screening using small hand-held gas detectors or "sniffing"
devices provides another fast and convenient way to detect accessible
leaks. Electronic gas detectors are equipped with catalytic oxidation and
thermal conductivity sensors designed to detect the presence of specific
gases. Electronic gas detectors can be used on larger openings that
cannot be screened by soaping. Electronic screening is not as fast as
soap screening (averaging 50 components per hour), and pinpointing
leaks can be difficult in areas with high ambient concentrations of hydro-
carbon gases.
* Organic Vapor Analyzers (OVAs) and Toxic Vapor Analyzers (TVAs)
are portable hydrocarbon detectors that can also be used to identify
leaks. An OVA is a flame ionization detector (FID), which measures the
concentration of organic vapors over a range of 9 to 10,000 parts per
million (ppm). A TVA combines both an FID and a photoionization detec-
tor (PID) and can measure organic vapors at concentrations exceeding
10,000 ppm. TVAs and OVAs measure the concentration of methane in
the area around a leak.
Screening is accomplished by placing a probe inlet at an opening where
leakage can occur. Concentration measurements are observed as the
probe is slowly moved along the interface or opening, until a maximum
concentration reading is obtained. The maximum concentration is
recorded as the leak screening value. Screening with TVAs is somewhat
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Exhibit 2. Acoustic Leak
Detection
slow—approximately 40 components per hour—and the instruments
require frequent calibration.
* Acoustic Leak Detection uses portable acoustic screening devices
designed to detect the acoustic signal that results when pressurized gas
escapes through an orifice. As gas moves from a high-pressure to a
low-pressure environment across a leak opening, turbulent flow pro-
duces an acoustic signal, which is detected by a hand-held sensor or
probe, and read as intensity increments on a meter. Although acoustic
detectors do not measure leak rates, they provide a relative indication of
leak size—a high intensity or "loud" signal corresponds to a greater leak
rate. Acoustic screening
devices are designed to detect
either high frequency or low
frequency signals.
High Frequency Acoustic
Detection is best applied in
noisy environments where the
leaking components are
accessible to a handheld sen-
sor. As shown in Exhibit 2, an
acoustic sensor is placed
directly on the equipment ori-
fice to detect the signal.
Alternatively, Ultrasound Leak
Detection is an acoustic
screening method that detects airborne ultrasonic signals in the frequen-
cy range of 20 kHz to 100 kHz. Ultrasound detectors are equipped with
a hand-held acoustic probe or scanner that is aimed at a potential leak
source from a distance up to 100 feet. Leaks are pinpointed by listening
for an increase in sound intensity through headphones. Ultrasound
detectors can be sensitive to background noise, although most detec-
tors typically provide frequency tuning capabilities so that the probe can
be tuned to a specific leak in a noisy environment.
Leak Measurement Techniques
An essential component of a DI&M program is measurement of the mass
emissions rate or leak volume of identified leaks, so that manpower and
resources are allocated only to the significant leaks that are cost-effective to
repair. Four leak measurement techniques can be used: conversion of TVA
and OVA screening concentrations using general correlation equations; bag-
ging techniques; high volume samplers; and rotameters.
Source: Physical Acoustics Corp.
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Data available for total fugitive emissions rates from gate stations and sur-
face facilities indicates that the leak rate for many components is relatively
small. For most gate stations, DI&M will only be cost-effective using the low-
est cost measurement technique, which is likely to be conversion of
TVA/OVA screening values using EPA correlation equations and TVA or OVA
instruments that may already be at hand.
* OVAs and TVAs can be used to estimate mass leak rate. The screening
concentration detected at a leak opening is not a direct measurement of
the mass emissions of the leak. However, the screening concentration in
ppm is converted to a mass emissions rate by using EPA correlation
equations. The EPA correlation equations can be used to estimate emis-
sions rates for the entire range of screening concentrations, from the
detection limit of the instrument to the "pegged" screening concentra-
tion, which represents the upper limit of the instrument. If the upper
measurement limit of the TVA is 10,000 ppm, a dilution probe can be
used to detect screening concentrations up to 100,000 ppm.
OVAs and TVAs must be calibrated using a reference gas containing a
known compound at a known concentration. Methane in air is a fre-
quently used reference compound. The calibration process also deter-
mines a response factor for the instrument, which is used to correct the
observed screening concentration to match the actual concentration of
the leaking compound. For example, a response factor of "one" means
that the screening concentration read by the TVA equals the actual con-
centration at the leak.
Screening concentrations detected for individual components are cor-
rected using the response factor (if necessary) and are entered into EPA
correlation equations to extrapolate a leak rate measurement for the
component. Exhibit 3 lists the EPA correlation equations for equipment
components at oil and gas industry facilities.
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Exhibit 3: U.S. EPA Leak Rate/Screening Value Correlation Equations
for Equipment Components in the Oil and Gas Industry
Equipment
Component
Valves
Pump Seals
Connectors
Flanges
Open-Ended
Lines
Other
Components
(instruments,
pressure
relief, vents,
all others)
EPA Leak Rate/Screening
Value Correlation
(kg/hr/source)
2.29E-06 x (SV)0746
5.03E-05 x (SV)0610
1.53E-06x(SV)0735
4.61E-06x(SV)0703
2.20E-06 x (SV)0704
1.36E-05x(SV)0589
Leak Rate Correlation
(kg/hr) for "Pegged"
Screening Value
>1 0,000 ppm
0.064
0.074
0.028
0.085
0.030
0.073
Leak Rate Correlation
(kg/hr) for "Pegged"
Screening Value
>1 00,000 ppm
0.140
0.160
0.030
0.084
0.079
0.110
The correlations presented are revised petroleum industry correlations. Correlations predict
total organic compound emissions rates.
Correlation factors for methane: 1 kg methane = 51 .92 scf; 1 kg/hr = 1 .246 Mcfd.
Source: U.S. EPA, 1995, Protocol for Equipment Leak Emission Estimates.
Exhibit 4 provides a table based on the above EPA correlation equations for
TVAs and OVAs. This can be used to estimate mass leak rate from the
screening concentrations detected at leaking components at gate stations
and surface facilities.
Exhibit 4. Example Screening Concentration/Leak Rate Correlations
Screening Concentration
(ppmv)
1
10
100
1,000
10,000
100,000
Screening value pegged
at >1 0,000
Screening value pegged
at >1 00,000
Estimated Mass Leak Rate (Mcf/yr)
Valves
0.001
0.006
0.032
0.180
1.004
5.593
29.109
63.676
Pump
Seals
0.023
0.093
0.380
1.547
6.301
25.669
33.657
72.773
Connectors
0.001
0.004
0.021
0.112
0.606
3.293
12.735
13.645
Flanges
0.002
0.011
0.053
0.269
1.360
6.864
38.660
38.206
Open-
Ended
Lines
0.001
0.005
0.026
0.130
0.655
3.313
13.645
35.931
Other1
0.006
0.024
0.093
0.362
1.404
5.450
33.203
50.031
1"0ther" equipment components include: instruments, loading arms, pressure relief valves,
stuffing boxes, and vents. Apply to any equipment component other than connectors,
flanges, open-ended lines, pumps, or valves.
Source: U.S. EPA, 1995, Protocol for Equipment Leak Emission Estimates.
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Bagging Techniques are commonly used to measure mass emissions
from equipment leaks. The leaking component or leak opening is
enclosed in a "bag" or tent. An inert carrier gas such as nitrogen is con-
veyed through the bag at a known flow rate. Once the carrier gas attains
equilibrium, a gas sample is collected from the bag and the methane
concentration of the sample is measured. The mass emissions rate is cal-
culated from the measured methane concentration of the bag sample
and the flow rate of the carrier gas. Leak rate measurement using bag-
ging techniques is accurate (within ± 10 to 15 percent) but, slow and
labor intensive (only two or three samples per hour). Bagging techniques
can be expensive due to the labor involved to perform the measurement,
as well as the cost for sample analysis.
High Volume Samplers capture all of the emissions from a leaking
component to accurately quantify leak emissions rates. Leak emissions,
plus a large volume sample of the air around the leaking component,
are pulled into the instrument through a vacuum sampling hose.
Sample measurements are corrected for the ambient hydrocarbon con-
centration, and mass leak rate is calculated by multiplying the flow rate
of the measured sample by the difference between the ambient gas
concentration and the gas concentration in the measured sample. High
volume samplers measure leak rates up to 8 cubic feet per minute
(scfm), a rate equivalent to 11.5 thousand cubic feet (Mcf) per day. Two
operators can measure 30 components per hour using a high volume
sampler, compared with two to three measurements per hour using
bagging techniques. High volume samplers can cost approximately
$10,000 to purchase. Alternatively, contractors can provide leak meas-
urement services at rate that ranges from $1.00 to more than $2.50 per
component measured.
Rotameters and other flow meters are used to measure extremely
large leaks that would overwhelm other instruments. Flow meters typi-
cally channel gas flow from a leak source through a calibrated tube.
The flow lifts a "float bob" within the tube, indicating the leak rate.
Because rotameters are bulky, these instruments work best for open-
ended lines and similar components, where the entire flow can be
channeled through the meter. Rotameters and other flow metering
devices can supplement measurements made using bagging or high
volume samplers.
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Decision
Process
Decision Steps for DI&M
1. Conduct baseline survey.
2. Record results and identify candidates for
repair.
3. Analyze data and estimate savings.
4. Develop a survey plan for future DI&M.
A DI&M program can be
implemented in four steps:
(1) conduct a baseline survey;
(2) record the results and
identify candidates for cost-
effective repair; (3) analyze the
data, make the repairs, and
estimate methane savings;
and (4) develop a survey plan
for future inspections and follow-up monitoring of leak-prone equipment.
Step 1: Conduct Baseline Survey. A DI&M program typically begins with
baseline screening to identify leaking components. For each leaking compo-
nent the mass leak rate is estimated using one of the techniques described
above. In the distribution sector, the emissions from leaking equipment com-
ponents at gate stations and surface facilities may be one or more orders of
magnitude less than emissions from leaks at compressor stations. For DI&M
to be cost-effective at gate stations and surface facilities, the baseline survey
costs must be minimal.
Some distribution sector partners elect to conduct leak screening only, using
very low cost and rapid leak detection techniques, which are incorporated
into ongoing maintenance operations. In these cases, all of the leaks that are
identified are repaired. A baseline survey that focuses only on leak screening
is substantially less expensive. However, leak screening alone does not
quantify leak rate or potential gas savings, each of which is critical informa-
tion needed to make cost-effective repair decisions in cases where partners
do not have the resources to repair all leaks.
Step 2: Record Results and Identify Candidates for Repair. Leak meas-
urements collected in Step 1 must be recorded to pinpoint the leaking com-
ponents that are cost-effective to repair.
As leaks are identified and measured, operators should record the baseline
leak data so that future surveys can focus on the most significant leaking
components. The results of the DI&M survey can be tracked using any con-
venient method or format. The information that operators may choose to col-
lect includes: (1) an identifier for each leaking component; (2) the component
type (e.g., gate valve); (3) the measured leak rate; (4) the survey date; (5) the
estimated annual gas loss; and (6) the estimated repair cost. This information
will direct subsequent emissions surveys, prioritize future repairs, and track
the methane savings and cost-effectiveness of the DI&M program.
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Natural Gas STAR partners report that the most common leaks at gate
stations and surface facilities are pinhole leaks and component flaws,
loose connections, and loose or worn valve stem seals. High frequency
leak locations identified by partners include: orifice plate/fittings, plugs
installed on test points, grease fittings on valves, multiple or large diameter
meter runs, couplings, valve stem packing, and flanges. The largest leaks
are generally located at pressure relief valves, open-ended lines, flanges,
gate valves, and gate valve stem packing. Leaks are prioritized by com-
paring the value of the natural gas lost with the estimated cost in parts,
labor, and equipment downtime to fix the leak.
Gate stations and surface facilities vary significantly in size and pressure
capacity depending upon the size and complexity of the distribution system.
As a result, there can be substantial variation in fugitive methane emissions
from such facilities. A 1994 field study sponsored by EPA and the Gas
Research Institute (GRI—now GTI, the Gas Technology Institute) used a trac-
er gas technique to measure total facility methane emissions at 40 gate sta-
tions and 55 district pressure regulators. This study found that average
annual methane emissions ranged from 1,575 Mcf per year for gate stations
with inlet pressures greater than 300 psig to less than 1 Mcf per year for dis-
trict regulators with inlet pressures less than 40 psig. Average annual facility
emissions, based on all 95 sample facilities were 425 Mcf. This study esti-
mated that a large component of total site emissions are contributed by
pneumatic controllers, which are designed to bleed gas to the atmosphere.
In 1998, EPA, GRI, and the American Gas Association Pipeline Research
Committee International (PRCI) conducted a second study of methane emis-
sions from equipment components at 16 natural gas metering and regulat-
ing facilities in transmission and distribution. Four of the facilities studied
were distribution system gate stations. This analysis included component
counts for each site, and leak screening and measurement of individual
component leaks using a high volume sampler. As in the earlier study, pneu-
matic controllers were found to contribute most of the total site emissions
(more than 95 percent). Because pneumatic devices are designed to bleed
gas during normal operation, these emissions are not considered leaks.
Pneumatic controllers provide a significant opportunity to reduce methane
emissions from gate stations and surface facilities, which is the subject of
Lessons Learned: Convert Gas Pneumatic Controls to Instrument Air and
Options for Reducing Methane Emissions from Pneumatic Devices in the
Natural Gas Industry.
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Exhibit 5. Average Emissions Factors for Equipment Leaks at Sixteen
Metering and Regulating Facilities
Component
Ball/Plug Valve
Control Valve
Flange
Gate Valve
Pneumatic Vent
Pressure Relief
Valve
Connectors
Total
Emissions Factor
(Mcf/yr/component)
0.21
0.46
0.13
0.79
134.3
4.84
0.11
Total Number
Components Screened
248
17
525
146
40
5
1280
2,261
Average Number
Components per Site
18
1
38
10
1
1
91
162
Source: Indaco Air Quality Services, 1998.
Exhibit 5 summarizes average component emissions factors obtained during
the 1998 field study. Approximately 5 percent of the 2,261 total components
screened were found to be leaking.
Exhibit 5 shows that pressure relief valves were found to be the largest leak
source, followed by gate valves and control valves. The smallest leaks were
found at connectors, flanges, and ball/plug valves. Exhibit 5 indicates that
the typical leak to be expected at gate state stations and surface facilities is
relatively small, and the number of components to be surveyed at each facil-
ity is over 100.
Based on the leak measurements of individual equipment components, the
1998 study determined the average total gas emissions from metering and
regulating facilities to be 409 Mcf per year. Excluding the total facility emis-
sions contributed by pneumatic controllers, the average total emissions con-
tributed by equipment leaks was in the range of 20 to 40 Mcf per site,
although substantial leaks in the range of 60 to 100 Mcf per year were
reported for some of the sites.
The 1998 field study reinforces the point made in Step 1, that a cost-effec-
tive DI&M program at gate stations and surface facilities must rely upon very
low cost and rapid screening techniques. Otherwise, the cost of finding the
leaks might not outweigh the savings gained from fixing the leaks.
Step 3: Analyze Data and Estimate Savings. Cost-effective repair is a criti-
cal part of successful DI&M programs because the greatest savings are
achieved by targeting only those leaks that are profitable to repair. Some
leaks can be fixed on the spot, for example, by simply tightening a valve-
stem packing-gland. Other repairs are more complicated and require equip-
10
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ment downtime or new parts. For these repairs, operators may choose to
attach identification markers, so that the leaks can be fixed later.
Easy repairs should be done on the spot, as soon as the leaks are found. In
all cases, the value of the gas saved should exceed the cost to find and fix
the leak. Partners have found that an effective way to analyze baseline sur-
vey results is to create a table listing all leaks with their associated repair
cost, expected gas savings, and expected life of the repair. Using this infor-
mation, economic criteria such as payback period can be easily calculated
for each leak repair. Partners can then decide which leaking components are
economic to repair.
Exhibit 6 provides an example of this type of repair cost analysis, which
summarizes the repair costs, total gas savings, and the estimated net sav-
ings for the anticipated repairs. The leak and repair data featured in Exhibit 6
are from the 1998 EPA/GRI/PRCI field study, during which leak repairs were
evaluated for two of the sixteen facilities included in the study.
Exhibit 6. Example of Repair Costs and Net Savings for Selected
Equipment Components
Component
Description
Ball Valve
Gate Valve
Gate Valve
Connectors
Sr. Daniel
Orifice Meter
Flange3
Type of
Repair
Re-grease
Replace
valve stem
packing
Replace
valve stem
packing
Tighten
Threaded
Fittings
Tighten
Fittings
Tighten
(estimated)
Repair
Cost1
(includes
labor &
material)
$13
$3
$3
$3
$33
$40
Total
Number of
Components
Fixed at Two
Sites
5
5
1
4
1
5
Total Gas
Savings
(Mcf/yr)
60 Mcf
67Mcf
92Mcf
11 Mcf
68Mcf
99 Mcf
Estimated
Net
Savings2
$/yr
$115
$36
$243
$21
$171
$97
Repair
Payback
Period
(Years)
0.4
0.8
0.1
0.4
0.2
0.7
'Average repair costs are in 2002 dollars.
2Assumes gas price of $3/Mcf.
3Repair cost not reported in original study. Flange repair cost estimated based on similar
1997 data on leak repair cost for "off-compressor" flanges at compressor stations.
Source: Indaco Air Quality Services, Inc., 1998, Trends in Leak Rates at Metering and
Regulating Facilities and the Effectiveness of Leak Detection and Repair (LDAR) Programs,
Draft Report.
11
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Because of safety concerns, some partners repair all leaks found af gafe
sfafions and mefer sfafions. In fhis case, a DI&M program may be useful for
improving fhe cosf-effectiveness of ongoing inspection and maintenance
operations by prioritizing repairs—the major leaks are identified and repaired
first, or inspection and maintenance is conducted more frequently at facilities
with the greatest leak frequency.
As leaks are identified, measured, and repaired, operators should record
baseline data so that future surveys can focus on the most significant leak-
ing components. This information will direct subsequent emissions surveys,
prioritize future repairs, and track the methane savings and cost-effective-
ness of the DI&M program.
Step 4: Develop a Survey Plan for Future DI&M. The final step in a DI&M
program is to develop a survey plan that uses the results of the initial baseline
survey to direct future inspection and maintenance practices. The DI&M pro-
gram should be tailored to the needs and existing maintenance practices of the
facility. An effective DI&M survey plan should include the following elements:
* A list of components to be screened and tested, as well as the equip-
ment components to be excluded from the survey.
* Leak screening and measurement tools and procedures for collecting,
recording, and accessing DI&M data.
* A schedule for leak screening and measurement.
* Economic guidelines for leak repair.
* Results and analysis of previous inspection and maintenance efforts
which will direct the next DI&M survey.
Operators should develop a DI&M survey schedule that achieves maximum
cost-effective gas savings yet also suits the unique characteristics of the
facility—for example, the age, size, and configuration of the facility and the
inlet pressure. Some partners schedule DI&M surveys based on the antici-
pated life of repairs made during the previous survey. Other partners base
the frequency of follow-up surveys on maintenance cycles or the availability
of resources. Since a DI&M program is flexible, if subsequent surveys show
numerous large or recurring leaks, the operator can increase the frequency
of the DI&M follow-up surveys. Follow-up surveys may focus on compo-
nents repaired during previous surveys, or on the classes of components
identified as most likely to leak. Over time, operators can continue to fine-
tune the scope and frequency of surveys as leak patterns emerge.
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Estimated
Savings
Savings achieved by Natural Gas STAR partners implementing DI&M pro-
grams at gate stations and surface facilities vary widely. Factors affecting
results include the number of stations in the DI&M program, the stage of
program development (i.e., new versus mature program), and the level of
implementation and repair costs. Costs differ between facilities because of
the type of screening and measurement equipment used, frequency of sur-
veys, and number and type of staff conducting the surveys.
Exhibit 7 provides a hypothetical example of the costs and benefits of imple-
menting DI&M at three gate stations. The leak rates and number of leaking
components in this example are based on actual leak rates reported for
three sites in the 1998 EPA/GRI/PRCI study. Exhibit 7 illustrates the type of
calculations that distribution partners should make to evaluate whether DI&M
could be cost-effective for their operations.
Exhibit 7 illustrates that although the costs of finding and fixing leaks may
not be recovered by the value of the gas saved at each and every site, if
multiple sites are included in the DI&M program, the overall program can still
be profitable. For the hypothetical example in Exhibit 7, DI&M is not cost-
effective at Site 2, although DI&M is profitable for the three sites considered
as a whole. In this case, the operator would use the experience gained from
the baseline survey of Site 2 to direct subsequent surveys; possibly exclud-
ing Site 2 from subsequent surveys, screening Site 2 less frequently, or
screening only a selected group of components.
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Exhibit 7. Example of Estimating the Savings from Implementing DI&M at
Gate Stations and Surface Facilities
General Assumptions:
Leak screening by soaping; 80 components
per hour
Leak measurement using TVA correlations
Hourly labor rate
TVA capital cost
Estimated repair life
2 hours x $/hour labor cost
1 hourx$/hour labor cost
$50/hour
$0 (assume already owned by partner)1
12 months
Sitel
Number of leaks
Hypothetical repair cost
Total gas savings
20 leaks (six valves repaired—2 x 30 Mcf/yr;
2x10Mcf/yr;2x1 Mcf/yr)
Assume 3 repairs x $10 and 3 repairs at $3
82Mcf
Site 2
Number of leaks (assume fewer leaks to
measure)
Hypothetical repair cost
Total gas savings
8 leaks (2x10 Mcf/yr; 6x2 Mcf/yr)
Assume 2 repairs x $5; 6 repairs at no cost
32Mcf
SiteS
Number of leaks
Hypothetical repair cost
Total gas savings
16 leaks (1x60 Mcf; 2x30 Mcf; 1x15 Mcf; 6x10
Mcf; 6x1 Mcf)
Assume 1 repair x $33; 2 repair x $15; 5 repair
x $3; remaining repairs at no cost
201 Mcf
Total Survey Total Repair Value of Gas
Cost Cost Saved ($3/Mcf)
Net Savings Payback Period
Sitel
Site 2
SiteS
Total
$150
$125
$150
$425
$39
$10
$78
$127
$246
$96
$603
$945
$57
($39)
$375
$393
9.2 months
17 months
4.5 months
7 months
1TVAs can cost up to $2,000. Savings from avoided emissions may not support purchasing a
TVA.
Partner Experience
From 1995 to 2000, 18 Natural Gas STAR partners reported gas savings
from implementing DI&M at gate stations and surface facilities. Three exam-
ples are shown in Exhibit 8.
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Exhibit 8: Partners' Experience Implementing DI&M at Gate Stations and
Surface Facilities
Company A: During 2000, this company surveyed 86 facilities and found leaks at 48 sites. A
total of 105 leaks were identified, and 66 leaks (63 percent) were repaired. The total cost to
find and fix the leaks was $2,453, an average of $29 per facility surveyed. Total gas savings
were 1,519 Mcf per year, worth $6,557 at $3 per Mcf. Total savings from DI&M was $4,104.
Net savings were approximately $50 per facility surveyed.
Total Gas Savings $6,557
Total Survey Costs $1,700
Total Cost of Repairs $753
Net Savings $4,104
Company B: Eighteen facilities were surveyed in 1997 for a total cost of $1,080. Fifteen small
leaks were identified including 1 flange, 2 swage lock fittings, and 12 small valves. The average
leak rate was 17.5 Mcf per year. The 15 leaks were repaired for a total cost of $380, which
resulted in gas savings of 263 Mcf per year. At $3 per Mcf, the value of the gas saved was
$789. The total cost of the leak survey and repairs, $1,460, was not recovered in the first year.
The average survey and repair cost was $60 per facility surveyed.
Total Gas Savings $789
Total Survey Costs $1,080
Total Cost of Repairs $380
Net Savings $(671)
Company C: This company surveyed 306 facilities and identified and repaired 824 leaks. Four
leaks were described as "large", seven were described as "medium", and the remaining leaks
were described as "small," meaning that an electronic detector or soaping was required to
locate the leak. Total survey and repair costs were approximately $16,500, an average of $54
per site surveyed. Total gas savings were 117,800 Mcf, an average of 143 Mcf per leak. Net
savings were approximately $1,100 per facility surveyed (at $3 per Mcf).
Total Gas Savings $353,430
Total Cost of Survey and Repairs $16,500
Net Savings $336,930
The number of facilities included in partners' DI&M programs ranged from
less than 20 facilities to more than 2,100 facilities. Leaks were found at 50
percent of facilities, and an average of two leaks were found per leaking
facility. The average emissions saved per leak repair was 100 Mcf per leak.
Partner-reported survey and repair costs varied substantially. Incremental
costs for DI&M surveys ranged from "negligible" for partners with ongoing
leak inspection programs already in place, to more than $1,200 per facility.
The highest DI&M survey costs were reported for large distribution systems
in urban areas where labor costs are higher, and the gate stations are pre-
sumed to be larger and to have more components. Reported repair costs
similarly ranged from negligible for simple repairs made on the spot, to more
than $500 per repair.
15
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Lessons
Learned
DI&M programs can reduce survey costs and enhance profitable leak repair.
Targeting problem stations and components saves time and money needed
for future surveys, and helps identify priorities for a leak repair schedule. The
principal lessons learned from Natural Gas STAR partners are:
* To be cost-effective, DI&M at gate stations and surface facilities must
use the most low cost and rapid screening and measurement tech-
niques. Soaping, listening for audible leaks, portable gas "sniffers," and
TVAs/OVAs are recommended for leak screening. TVA screening con-
centrations and EPA's correlation equations are recommended as a
cost-effective method for estimating mass leak rate, especially if a TVA
or OVA is already available at the facility.
* A small number of large leaks contribute to most of a facility's fugitive
methane emissions. Partners should focus on finding leaks at equipment
components that are cost-effective to repair. One of the most cost-effec-
tive repairs is simply to tighten valve packings or loose connections at
the time the leak is detected. Partners have found it useful to look for
trends, asking questions such as "Do gate valves leak more than ball
valves?"
* Partners have also found that some sites are more leak-prone than oth-
ers. Tracking of DI&M results may show that some facilities may need
more frequent follow-up surveys.
* Institute a "quick fix" step that involves making simple repairs to simple
problems (e.g., loose nut, valve not fully closed) during the survey
process.
* Re-screen leaking components after repairs are made to confirm the
effectiveness of the repair. A quick way to check the effectiveness of a
repair is to use the soap screening method.
* Frequent surveying (e.g., quarterly or twice yearly) during the first year of
a DI&M program helps identify components and facilities with the high-
est leak rates and leak recurrence, and builds the information base nec-
essary to direct less frequent surveying in subsequent years.
* Record methane emissions reductions for each gate station and/or
other surface facilities and include annualized reductions in Natural Gas
STAR Program reports.
16
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Bascom-Turner Instruments, personal communication.
References
Foxboro Environmental Products, personal communication.
Gas Technology Institute (formerly the Gas Research Institute), personal
communication.
Henderson, Carolyn, U.S. EPA Natural Gas STAR Program, personal com-
munication.
Indaco Air Quality Services, Inc., 1995, A High Flow Rate Sampling System
for Measuring Leak Rates at Natural Gas Facilities. Report No. GRI-
94/0257.38. Gas Technology Institute (formerly Gas Research Institute),
Chicago, IL.
Indaco Air Quality Services, Inc., 1998, Trends in Leak Rates at Metering and
Regulating Facilities and the Effectiveness of Leak Detection and Repair
(LDAR) Programs, Draft Report prepared for PRC International, Gas
Research Institute, and the U.S. Environmental Protection Agency.
Radian International, 1996, Methane Emissions from the Natural Gas
Industry, Volume 2, Technical Report, Report No. GRI-94/0257.1. Gas
Technology Institute (formerly Gas Research Institute), Chicago, IL.
Radian International, 1996, Methane Emissions from the Natural Gas
Industry, Volume 10, Metering and Pressure Regulating Stations in Natural
Gas Transmission and Distribution, Report No. EPA600-R-96-080J.
Tingley, Kevin, U.S. EPA Natural Gas STAR Program, personal communication.
U.S. Environmental Protection Agency, 1994-2001, Natural Gas STAR
Program, Partner Annual Reports.
U.S. Environmental Protection Agency, 1995, Natural Gas STAR Program
Summary and Implementation Guide for Transmission and Distribution
Partners.
U.S. Environmental Protection Agency, 1995, Protocol for Equipment Leak
Emission Estimates, Office of Air Quality Planning and Standards, EPA453-
R-95-017, November 1995.
U.S. Environmental Protection Agency, 2001, Lessons Learned: Convert
Gas Pneumatic Controls to Instrument Air, EPA430-B-01-002.
U.S. Environmental Protection Agency, 2003, Lessons Learned: Options for
Reducing Methane Emissions from Pneumatic Devices in the Natural Gas
Industry, EPA430-B-03-004.
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&EPA
United States
Environmental Protection Agency
Air and Radiation (6202J)
1200 Pennsylvania Ave., NW
Washington, DC 20460
EPA430-B-03-007
October 2003
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