MTBE and Pressurized Piping

In July and September 1999, two significant reports were published on methyl tertiary butyl ether (MTBE) contamination in groundwater.

In July and September 1999, two significant reports were published on methyl tertiary butyl ether (MTBE) contamination in groundwater. In January 2000, CBS News’ 60 Minutes devoted two segments to MTBE contamination, calling it “the biggest environmental crises of the next decade.”

It was reported that MTBE was detected even where potential contributing underground fuel handling systems were “tight” under the Environmental Protection Agency’s (EPA) underground storage tank (UST) release and detection rules. Thus, incidental delivery and refueling spills are suspected.

This column addresses another factor, the high vapor pressure of MTBE (i.e., 25 times greater than benzene when corrected for its composition in gasoline) and the possibility that allowable permeation levels for product piping could be a future source of MTBE contamination.

Based on recent testing evaluations, manufacturers of UL-Listed fiberglass pipe recommend a 95 percent reduction in the permeability level allowed in the UL 971 test protocol.

Santa Clara Valley report
The July report was on a groundwater vulnerability pilot study by the Santa Clara Valley Water District. The study was to determine the occurrence of MTBE at sites with operating UST/piping systems and to identify whether MTBE is being released undetected at facilities with 1998-upgrade compliant UST/piping systems.

Field investigations were conducted at a cross-section of 27 sites where groundwater was encountered and previously known contamination had not occurred. MTBE was detected in groundwater at 13 of the 27 sites. However, petroleum constituents were not detected in groundwater at 5 of the 13 where MTBE was detected. As a result, the study concluded that the greater frequency of MTBE detection relative to petroleum constituents likely results from:

• Increased solubility and mobility of MTBE
• Possible vapor release and migration of MTBE in the vapor phase
• The large faction of MTBE in the fuel mixture relative to petroleum compounds
• Recalcitrance of MTBE to biological degradation relative to petroleum compounds

The study also concluded that the type of storage tank (e.g., steel or FRP) made no difference.

Blue Ribbon Panel report
The September report was by the Blue Ribbon Panel on Oxygenates in Gasoline, which was appointed by EPA Administrator Carol Browner to investigate the air quality benefits and water quality concerns associated with oxygenates in gasoline, and to provide independent advice and recommendations on ways to maintain air quality while protecting water quality. The report states that “the use of MTBE . . . has resulted in growing detection of MTBE in drinking water, with between 5% and 10% of drinking water supplies in high oxygenate use areas showing at least detectable amounts of MTBE.” As a result, along with other recommendations, the Panel recommended that EPA “evaluate the field performance of current system design requirements and technology and, based on that evaluation, improve system requirements to minimize leaks/releases . . . .”

News programs such as 60 Minutes and other published reports have highlighted the issue of MTBE contamination, likely sources and the need for solutions. As discussed below, the Fiberglass Tank & Pipe Institute believes that permeation of product piping could be a source of contamination and that the level of permeation allowed in petroleum piping systems can and should be reduced by 95 percent.

Permeation in pressurized piping systems
“Permeation” is defined in Webster’s as the process of diffusing through or penetrating something. The example given is tobacco smoke when it spreads or diffuses through air in a room. A practical level of permeation will occur throughout a pressurized dispensing system where there are threaded or sealed joints (e. g., tank bungs, pump inlets and outlets, flex connectors, flexible piping, safety shear valves, filter connections, meter connections, meter seals, hose connections, hoses, break-away connections, swivels and nozzles and vapor recovery components).

Historically, permeation was not believed to be a concern for steel piping systems when used in flammable and combustible liquid applications, or for fiberglass piping when used in petroleum applications that date back to the 1950’s to transport corrosive crude oils in production fields.

Moreover, potential permeation was not an issue when, beginning in 1967, the American Petroleum Institute (API) published four standards for the different designs of fiberglass piping used in low- and high-pressure (i. e., up to 5,000 psi) applications. Later, there was an effort to mitigate the corrosion failure of underground steel piping used in vehicle refueling facilities. Concern for public safety prompted the need for a pressure-piping permeability test protocol.

In 1973, fiberglass manufacturers and Underwriters Laboratories (UL) engineers developed UL 971, Nonmetallic Underground Piping for Flammable Liquids, to ensure that non-metallic piping used for flammable and combustible liquids was a safe substitute for the steel piping it was replacing. Finally, in 1988, after an EPA performance evaluation, this UL 971 standard was referenced as a method to meet the federal UST regulations.

UL 971 test protocol
UL 971 contains a permeability test protocol to determine the rate of permeation for various non-metallic piping materials. The protocol is used to test specimens of primary and secondary containment pipe. The specimens consist of 18–inch lengths of pipe and the end sealing methods (e. g., end caps). These specimens are weighed empty, then filled with the test liquid (e.g., fuel oil, leaded and unleaded gasoline, methanol or ethanol), sealed and weighed again. The loss of liquid (i. e., permeation loss) is calculated monthly for a period of 180 days for the primary pipe and twice a week for 30 days for the secondary pipe. The permeation rate is calculated based on the internal surface area of the pipes that are weighed empty.

Originally, the UL 971 permeability test protocol applied to primary piping only and stated that “there shall be no loss of weight in any of the test samples” (i. e., no permeability) over the test period. However, this “no loss of weight provision” proved too absolute to be practical with all pipe materials, including steel and threaded joints, even when sealed with the best of the thread-sealing compounds. Testing experience shows that pipe sealing and weighing accuracy are imperfect and will confound the testing results.

As a result, UL and pipe manufacturers agreed to an allowable weight loss of up to one percent of the weight of the sample liquid. Although not published in a revised standard, the one percent permeability allowance was believed to be a deminimus amount and was applied in the test protocol.

This practical allowance for testing results variability was recognized by EPA when it developed the UST leak rate test protocol. While the goal is to have leak-free UST systems, the EPA criteria for passing the tank tightness test is to detect a leak as small as 0.1 gallon per hour and greater. This is a practical test protocol because it recognizes that testing variability will occur when a tight system is tested.

Later in 1995, UL changed the permeability test for primary and secondary piping to permit a permeation rate of up to 4 g/sq. meter/day for the primary and 24 g/sq. meter/day for the secondary containment piping. Thus, the revised UL 971 permits a permeability leakage of:

• 0.16 gallons per 100 feet in 30 days in a 2-inch I.D. Primary pipe
• 1.0+ gallons per 100 feet in 30 days in a +2-inch I.D. Secondary pipe

Applying the above criteria to a medium-sized refueling facility with 500 feet of piping, the allowed permeation for the primary piping would amount to nearly one gallon (more than 0.8 gallon) per month.

Institute recommendation
In October 1999, UL representatives attended a meeting with the users of UL 971-listed piping products. Certain petroleum industry meeting participants reported that attendees expressed the concern that the existing high UL 971 permeability allowance levels were too high. It was further reported that the concern centered on allowing high levels of certain gasoline constituents to permeate into the environment. While natural biodegradation neutralizes gasoline hydrocarbon components, MTBE is slow to biodegrade and high levels of piping permeation are a concern.

The Fiberglass Tank & Piping Institute has expressed concern to EPA and UL that the current UL 971 test protocol does not recognize the risks associated with allowing higher permeation levels of gasoline hydrocarbons, gasoline additives and oxygen components that might escape into the environment. In fact, Institute member companies believe that the permeability test protocol should be more stringent than the previously allowable one percent of the sample liquid’s weight.

The Institute believes that the allowable permeation rate for the primary piping should not be greater than 0.2 g/sq. meter/day. This recommendation, made by the Institute to UL earlier this year, represents a 95 percent reduction from the 4 g/sq. meter/day allowed in current UL 971 test protocol. This is achievable, will minimize contamination due to potential piping permeability and will allow for testing and measurement variability rather than an absolute zero criterion.

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