United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-83-099 Feb. 1984
&ER& Project Summary
Fail-Safe Transfer Line for
Hazardous Fluids
A. J. Houghton and J. A. Simmons
A fail-safe transfer line for hazardous
liquids was designed, fabricated, tested
in the laboratory, and then used in
actual fluid transfer operations. The
system provides a 2-in.-ID flexible hose
line for offloading tank cars or trucks
and detects leaks by monitoring flow
inventory with corrosion-resistant,
turbine-type flow meters at the inlet
and outlet ends. Reliable shutdown of
the line at leak rates as low as 1 % of flow
is achieved. As an example, at a flow of
6 liters/sec (100 gal/min), shutdown
occurred within 8 sec with a fluid loss of
less than 500 ml (1 pint). The line is also
automatically shut down when elec-
trical power or valve actuator pressure
is lost, or when any sensor or control
cable is severed. The system meets the
National Electrical Code explosion-
proof standards for Class I, Division I,
Group C or D environment. Use-
demonstration tests at a chemical plant
were satisfactory except for occasional
fouling of the flow meters with material
that solidified in the transfer hose
between operations. The system is
recommended for use with materials
that remain in a liquid state under a|l
normal conditions.
This Project Summary was developed
by EPA's Municipal Environmental
Research Laboratory, Cincinnati, OH,
to announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
The report describes the development
of a fail-safe transfer line for hazardous
liquids. The principal requirement was
the reliable, automatic shutdown of the
transfer line in response to a leak that
was well below the magnitude that could
be controlled by an excess flow valve
(rising ball type). Additional requirements
included shutdown of both ends of a
leaking or severed line to prevent back-
siphoning, shutdown of the line when
any of the conditions necessary for its
reliable operation (e.g., electrical power
or air pressure) were not satisfied, a
means to verify operability at time of use,
and the ability to handle many types of
hazardous liquids. The contract specified
that the entire system be constructed
from off-the-shelf components of standard
industrial quality. The transfer line was
designed to handle the loading and
unloading of railroad tank cars and tank
trucks.
The project encompassed four areas of
effort.
Systems Design
This task involved the analysis of
alternative methods for sensing leaks and
the design of all components for the
transfer line. The governing criteria were
reliability, cost, and compatibility with the
hazardous materials to be handled during
the demonstration tests.
Assembly and Development
Tests
This task included the acquisition of all
components, construction of the line, and
testing of the line in a controlled
environment using water as the liquid.
During the development phase, the
design was optimized to achieve the best
practical capability for detection of small
leaks.
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Use-Demonstration Tests
In this task, the line was used in an
industrial environment at the Goodyear
synthetic rubber plant in Houston, Texas,
to offload railroad tank cars of TAMOL-L,
an aqueous solution of the sodium salt of
a naphthalene-sulfonic acid.
Analysis and Reports
This task included analysis of data and
the preparation of a final report.
Application of this transfer line (or its
principle) to all loading and offloading of
hazardous and polluting liquids could
result in a significant reduction in the
number of spills. According to a study of
reported spills of hazardous materials in
the United States during the period of
January 1, 1971, to June 30, 1973, the
failure of a hose or transfer line resulted
in 92 spills or 7% of all spills reported.
Similarly, an analysis of bulk liquids spills
atU.S. marineterminalsduring 1974and
the first 8 months of 1975 revealed that
7.5% (108 out of 1,441) during cargo
transfer operations resulted from the
failure of the hose or pipeline. When
these data are considered along with the
frequency of loading and offloading
operations they indicate that a hose or
pipe failure results in one spill for every
1,000 transfers. The spill rate for all
causes of spills at marine terminals dur-
ing loading and offloading of bulk liquid
cargos is approximately 12 per 1,000
operations.
Design and Development
The basic concept of the transfer line is
illustrated in Figure 1. A flexible line is
equipped with essentially identical inlet
and outlet assemblies. Each assembly
contains a fast-acting, remotely operated
valve and a device to measure fluid flow.
A control module compares the flow
measurements at each end. Upon detec-
tion of a flow imbalance, the control
module automatically causes the valves
at each end to close. In addition to flow
comparison, the system incorporates
other fail-safe features:
1. Automatic valve closure when any
of the conditions necessary for safe
operation are not satisfied (e.g., loss
of air pressure or electric power).
2. A means for verifying proper opera-
tion at any time during a transfer
operation.
As specified in the statement of work,
the criteria for selecting components,
materials, and techniques were reliability,
compatibility with the material to be
handled, off-the-shelf availability, cost, and
(for the portable parts of the system) weight.
In the original plan, the material to be
handled during the use-demonstration
phase was aniline, which required that
the electrical portions meet the National
Electrical Code explosion-proof standards
for Class I, Division I, Group C and D
materials.
The selection of valves and actuators
quickly converged upon pneumatically
operated, stainless steel ball valves. Gate
and globe valves require motor driven
actuators. These assemblies are relatively
slow-acting and are heavier and more
expensive than the ball valve/pneumatic
actuator combination. Solenoid actuators
were available for the ball valves but were
too heavy (more than 60 Ib) for portable
use. Brass is incompatible with many
fluids, and reliability considerations
argued against the use of aluminum. The
pilot valve required for remote operation
of the pneumatic actuator weighed less
than 1 Ib and is available in a compatible,
explosion-proof configuration.
Stainless steel was selected for the
pipe fittngs because of its superior
reliability. Further, since no margin of
safety was needed to compensate for
corrosion, lighter weight pipe could be
used. The dominant criterion for the hose
was reliability. A 2-in.-ID, rubber-
impregnated, steel-reinforced steam
hose was selected. This hose was
essentially identical to those used at the
use-demonstration site for offloading _
aniline. •
The flow measurement sensors that ^
were evaluated were (in order of increas-
ing cost) thermistors, thermal probes,
turbine flow meters, and venturi tubes
with differential pressure gauges. Analy-
sis indicated that any available thermistor
with an envelope compatible with aniline
would have too slow a time constant to
meet the leak detection objective. Thermal
probes appeared to meet all criteria and
were initially selected for the development
phase. These sensors operated well with
clear liquids. However, with slightly dirty
fluids, the probes developed instabilities
that were unacceptable. Turbine flow
meters were next selected and were
satisfactory.
The control module was designed with
integrated circuits throughout for reliabil-
ity and small size. Transistor-Transistor
Logic (TTL) was selected because of its
reliability.
The major hardware items were
assembled and set up in a laboratory
shop. A 200-gal tank and a 2-HP pump
were used to provide a flow through the
system. A reducing tee with a needle
valve and a ball valve in series was
inserted between the flow meters to
permit controlled leakage. The electronic
circuits were breadboarded for easy
access to test points, and special circuits
Air Supply
I
Vent
Flow Comparator and
Valve Logic
Supply Vessel
I I
I I
i
I
L .
Receiving Vessel
FS Flow Sensor
SV Solenoid Valve
AO Air Operated Valve
Note: All valves are shown in the'de-energized position.
Figure 1. Basic concept of fail-safe transfer line.
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for diagnostics and data acquisition were
fabricated. Figure 2 shows the inlet
assembly. The outlet assembly is identical
except that the strainer is omitted.
The turbine flow meters used consist of
a turbine wheel mounted axially in a
short length of non-magnetic pipe. Two of
the turbine blades have magnets inserted
into their outer ends, and a coil on the
outside of the pipe produces a low-level
AC signal when the turbine rotates. The
frequency of the signal is proportional to
the flow rate over the operating range of the
device. Flow meters are individually
calibrated, and it is unlikely that two will
have identical K factors (the K factor is the
number of alternating current cycles that
will be generated for each gallon of fluid
passing through the meter). Furthermore,
it is necessary to provide compensation
for unequal wear with prolonged use. A
rate multiplier circuit is used with the
fastest (highest K factor) meter. The
output of the rate multiplier circuit, f(out),
is
f(out) = f(in) x m
4096
where m is any desired integer between 0
and 4095. Thus the meter indication can
be synchronized to within 2.4 parts in
10,000.
The basic logic circuit is an up-down
counter. The pulses from the inlet flow
meter (normalized by a rate-multiplier
circuit) cause the counter to count up;
those from the outlet flow meter cause
the counter to countdown. After a pre-set
number of total pulses (a frame) is
received, the balance shown by the up-
down counter is read electronically, after
which the counter is reset for the start of
the next frame. The assumption is that
there is no line leakage when the count
balance is zero, however, there may
actually be a net count (but no leak)
because of air bubbles, hose pulsing,
solid particles, or other flow anomalies.
The distribution of the balances on the
counter was recorded for leak rates from
0% to 4% of flow. Experiments show that
a frame of about 1,000 total pulses
provides an adequate sample period to
average out most naturally occurring
variations in flow. For convenience in
using digital logic, the frame count is set
at 1,024 pulses, corresponding to the
passage of about 7.1 liters (1.88 gal)
through the system. Figure 3 shows the
distribution of indicated flow imbalances
for leak rates of 0% and 1.5% of flow rate.
Since the up-down counter reading. A,
differed from zero too frequently under
no-leak conditions and the line was shut
down too often, a comparator was built to
Pneumatic Valve
Actuator
Jamesbury ST-SOE
Explosion Proof
Pilot Valve
ASCO8345-11
500 cc Stainless
Steel Air Reservoir
\
Stainless Steel Check Valve
1 /4" dia STS >4/
Line
Portable Cable
to Control Module
Explosion Proof
Junction Box
Crouse-Hindsi
GUAC-16
Potting Head
Grouse-Hinds
CGSP-194
Portable
Cable to
Control
Module
Strainer
(Omit on Outlet
Assembly)
Figure 2. Inlet assembly.
2" dia Ball Valve
Jamesbury A3600 JT
Model B
Cox Flow Meter
Dashed line is average
for all observations.
Shaded area shows range
for successive 100-sample
trials.
Probability that meter outputs will differ by f) counts in one frame
under no leal! conditions.
0.5
0.4
.£ 0.3
S 0.2
a.
0.1
/\
Figure 3.
2 4 6 8 10
n
Same as Above, but with a /.5% of Flow Leat Introduced
Distribution of flow imbalance indicators, 0 and 1.5% leak rates.
3
12
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show how A compared with B, a presel-
ected number or threshold for shutdown.
The comparator output indicates whether
A is greater than, equal to, or less than B.
At the end of each frame, the comparator
output is read. When, for example, B is set
at 4 and A has a value of 6, the flow
imbalance exceeds the switch-selected
threshold, indicating a leak (or, more
properly, the possibility of a leak). Under
no-leak conditions, the up-down counter
balance rarely exceeded 4 but did
occasionally read higher.
The system was then operated with
various leak rates and values of B. The
ratio of leak to normal indications, the
number of successive leak indications
occurring between two normal indica-
tions, and the number of successive
normal indications occurring between
two leak indications were recorded and
their distributions were determined.
These data formed the basis for
designing additional circuitry. Analysis of
the data showed that the reliable detection
of small leaks (less than 2% of flow) could
not be done on a single frame indication
without a high false alarm rate. By
increasing the number of frames used to
conclude that a leak existed, the false
alarm rate could be suppressed. The
penalty imposed was an increased time
duration for the leak to exist before
shutdown.
Based on the above stated conclusions,
an additional count register circuit was
installed. The count, C, displayed on the
register increased each time the compar-
ator (A vs. B) output indicated a leak
(A>B), but the register was cleared to
zero each time two successive normal
(A=B or A
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was TAMOL-L concentrate, an aqueous
solution of the sodium salt of naphthalene-
sulfonic acid. The testing site was the
Goodyear synthetic rubber plant in
Houston, Texas. The system was installed
by Goodyear personnel at the TAMOL-L
concentrate storage tank site. Offloading
stations for both tank cars and tanktrucks
were in the immediate vicinity of the tank.
An expansion of the plant was in
progress, and access to the truck off-
loading stations was blocked by construc-
tion work. Consequently, only tank cars
were offloaded. Seven tank cars with an
average load of 8,000 gal each were
offloaded in 6 test days. No actual leaks
were encountered. During the third
unloading operation, a small leak was
induced by loosening a pipe coupling at
the point where the hose was attached to
the outlet (storage tank) exit. The line shut
down automatically within 8 sec. An
estimated 1 pint of fluid was lost before
shutdown.
Some difficulties were encountered in
the demonstration tests, all attributable
to the nature of the material handled.
TAMOL-L contains more than 50%
dissolved solids. Upon prolonged exposure
to the atmosphere, the vehicle (water)
evaporates, leaving a residue that varies
from semi-solid to solid. When the
transfer line was not completely purged
after each use, the residual material dried
out, leaving a coating of solids on the
internal surfaces. Upon reuse of the line,
the fresh fluid caused pieces of the solid
material to slough off, fouling the outlet
flow meter. A period of 2 to 15 min of flow
(depending on the temperature of the
fresh fluid and the degree of solidification
of that which coated the internal surfaces)
was usually required to establish trouble-
free operation.
In general, the use-test period was
successful in that it demonstrated that
the system did not impose any significant
increase in labor or inconvenience during
its use. However, the specific nature of
the material handled created problems
that would require an additional step—
flushing the system with water—when
the time between transfer allowed the
material to solidify.
Conclusions and
Recommendations
The detection of small leaks (on the
order of 1% of flow rate) in a liquid
transfer line between storage facilities
and tank cars or tank trucks is feasible
using a flow balance comparison system
constructed of commonly available
components. Rapid, automatic closure of
both ends of the line upon detection of a
leak is simple to accomplish.
Naturally occurring variations in volu-
metric flow (presumably caused by
dissolved compressible gases, flow
cavitation, and the elasticity of the
transfer line) preclude the reliable
detection of very small leaks within the
tolerance of the flow sensors on a single-
event basis.
As built under this contract with
standard discrete components, the fail-
safe system for the automatic shutdown
of a transfer line in response to a small
leak is relatively cumbersome. A signifi-
cant portion of the size and weight results
from the need for pip-unions, nipples,
couplers, junction boxes, and other items
required to integrate the components.
A fail-safe transfer system that em-
bodies the features of the system
described in this report is applicable to
nearly any transfer line or conduit
handling noncompressible fluids with a
viscosity and flow rate within the
operating range of available turbine flow
meters. The size of the line and the
materials used may be varied to suit
different flow rates and fluids. The size,
weight, and cost of a system comparable
with the one described in this report can
be significantly reduced by: (1) the
development of inlet and outlet modules
that have integral valves, activators, pilot
valves, flow meters, junction boxes, etc.,
and (2) the development and certification
of an intrinsically safe control module.
The foregoing recommendations for
improved design are not economically
practical for systems manufactured in
small quantities. However, the prototype
system was deemed usable without
special handling equipment by product
transfer personnel at the industrial plant
where the system was evaluated.
A fail-safe transfer system functionally
similar to the one described in this report
should be considered for use in the
transfer of particularly hazardous materials
between storage facilities and tank cars
and tank trucks.
The full report was submitted in
fulfillment of Contract No. 68-03-2039 by
Science Applications, Inc., under the
sponsorship of U.S. Environmental
Protection Agency.
A. J. Houghton and J. A, Simmons are with Science Applications. Inc.. McLean,
VA22102.
John E. Brugger is the EPA Project Officer (see below).
The complete report, entitled "Fail-Safe Transfer Line for Hazardous Fluids,"
(Order No. PB 84-112 705; Cost: $8.50, subject to change) will be available only
from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Municipal Environmental Research Laboratory -Cincinnati
U.S. Environmental Protection Agency
Edison, NJ 08837
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United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
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