Detection of interstate liquids pipeline leaks: Feasibility evaluation Page: 8 of 14
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to 0.4% of total flow under ideal conditions. On the main Colonial pipeline, 0.3% of 2.5x106
GPH is a 7,500-GPH leak detection threshold-much too large except for major pipeline failures.
Table 1 gives examples of the three primary, commercially-available technological
approaches. APS/EFA offer the flow-totalizng mass-balance approach which may be cost effective
for quick response to major failures. ASI offers an acoustic-based technique based on pressure-
wave propagation from a sudden pressure loss; on a 4-ft diameter hydraulic pipeline system, a
major leak will be required to initiate a significant-enough pressure loss. Again, this system may
also be cost-effective for alarming of major leaks.
The third technique, a tracer vapor-based approach, is available from two sources. From
TRC, below-ground soil air is analyzed for the presence of tracer vapors escaping from the leaking
fuel. It would not be cost-effective to use their soil-air vapor extraction approach along thousands
of miles of pipeline, but very small leaks would be detectable. Brookhaven's tracer vapor
approach, however, would be cost effective.
This last approach, based on Brookhaven's PFT technology, is a commercially-accepted
system for pinpointing underground dielectric fluid leaks of less than 0.1 GPH from such
circulating (up to 25,000 GPH), but not consumed, fluids in pipelines.(') In Table 1, it is estimated
that based on even further improvements in this technology, supported both by the Consolidated
Edison Company of New York, Inc.4) and several federal agencies, mobile leak surveys by
driving along the pipeline at about 15 to 20 mph will be able to detect Colonial pipeline leaks of as
little as 1GPH-that is, less than 0.0001% of flow rate or more than 3 orders-of-magnitude better
than any on-line system.
The next section provides some details of the proposed PFT approach and some technical
description of the envisioned process.
Detection Surveying for Oil Pipeline Weepage
The proposed approach for small-leak detection is based on the cost-effective PFT tagging of
a batch of gasoline for about 2 days, followed by a continuous leakmobile surveying (i.e., driving)
of the pipeline route using a new-generation quasi-real time analyzer, looking for the presence of a
subsurface gasoline leak as indicated by the emission of vapors from the PFT tag, in this case, a
PFT that has never previously been manufactured and which should have a background
concentration comparable to the new instrument's detection limit.
Tagging, emission rates, and peak above-ground air concentration. The assumed
specifications of the pipeline are given in Table 2. A 2.9 million barrel batch of gasoline, tagged
for 48 hours (2 days) at 10 ppb by wt of PFT, will be transported about 115 miles per day. The
total of 3.5 kg of PFT would only cost $1400 for the 2 days of tagging. If a 55-gallon drum of
tagging fluid is prepared at 10% by weight of octane (gasoline), then a 10- dynamic dilution of that
solution would establish the desired final 10 ppb concentration. As shown in Table 2, the
metering rate of only 15.8 mL/min would, in 48 hours, consume less than 1/4 of the drum's
contents; a single drum could thus be used to perform up to 4 separate surveys of the total pipeline
system traversed by the tagged batch of gasoline.
The leak rate emissions of both PFT vapors and gasoline vapors into the air at steady state
(about 24 to 48 hours after the arrival of tagged gasoline) would, for a 1-GPH leak occurring 6 feet
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Dietz, R.N. & Senum, G.I. Detection of interstate liquids pipeline leaks: Feasibility evaluation, report, October 20, 1998; United States. (https://digital.library.unt.edu/ark:/67531/metadc684035/m1/8/: accessed April 25, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.