On January 3, 2011, the National Transportation Safety Board (NTSB) issued a series of urgent pipeline-safety recommendations based on preliminary findings from the September 9, 2010, gas-transmission-pipeline rupture in San Bruno, California. The NTSB investigation determined that PG&E's pipeline records were inaccurate and potentially resulted in an inappropriate maximum allowable operating pressure (MAOP) for the line in question.

The resulting urgent safety recommendations "call on pipeline operators and regulators to ensure that the records, surveys, and documents for all pipeline systems accurately reflect the pipeline infrastructure as built throughout the U.S. so that maximum safe operating pressures are accurately calculated."

The new recommendations stem from a particular finding. At the rupture site, several short pup joints of pipe had longitudinal-seam types that did not match recorded pipe properties. The pup joints had fusion-welded seams, but records indicated the pipe was seamless. The difference is critical, because some classes of fusion-welded pipe are not as strong as seamless pipe. In fact, the American Society of Mechanical Engineers B31.8 standard requires MAOP for such pipe to be reduced to 80% of the MAOP for otherwise similar seamless pipe.

"The pipeline regulations were originally put in place in 1970," explains Tracy Thorleifson, vice president ofEagle Information Mapping Inc. "Some operators at that time didn't have sufficient records or qualifying pressure tests to fully comply with them. So a special grandfather provision was put into the regulations with respect to MAOP."

Eagle Information supplies geographic-information-system data to midstream companies, which use the information to comply with current regulations. Thorleifson's group closely scrutinizes the regulatory environment and updates its software accordingly.

"The special provision (Title 49: Transportation, Part 192—Transportation of natural and other gas by pipeline: minimum federal safety standards, section 192.619(c)) allowed the existing pipeline systems to be grandfathered under the rule so that they could operate at higher MAOP than the rule would otherwise allow."

The grandfather provision stated that operators only had to document the highest operating pressure over the five-year period prior to July 1, 1970. The operators could use that peak as their MAOP limit going forward.

"After the San Bruno accident, it was discovered that PG&E's records were inaccurate. Since then, the NTSB has said that pipeline operators must scour their records and be able to demonstrate to auditors that all of the information required to calculate a design-based MAOP is available and accurate. If an operator cannot produce that documentation, a pressure test must be documented or undertaken.

"As expanding suburbia encroaches on pipeline rights-of-way, the Department of Transportation (DOT) class location category increases. This is because DOT class location is basically a measure of housing density around the pipe. An increase in class location nullifies the exemption for grandfathered pipe. For many operators, the course of least resistance is to convert to an MAOP based on design pressure," says Thorleifson.

However, in its January 4 Advisory Bulletin ADB-11-01, the Pipeline and Hazardous Materials Safety Administration (PHMSA) reiterates, "Operators relying on the review of design, construction, inspection, testing and other related data to calculate MAOP or MOP must assure that the records used are reliable. An operator must diligently search, review and scrutinize documents and records, including but not limited to, all as-built drawings, alignment sheets, and specifications, and all design, construction, inspection, testing, maintenance, manufacturer, and other related records. These records shall be traceable, verifiable, and complete. If such a document and records search, review, and verification cannot be satisfactorily completed, the operator cannot rely on this method for calculating MAOP or MOP."

The bulletin continues with the admonition, "Future PHMSA inspections will place emphasis on the areas noted in this Advisory Bulletin."

"PHMSA has made it clear that recently expanded comprehensive audits will place an emphasis on scrutinizing all records related to MAOP," says Thorleifson. "This is going to put extreme pressure on operators with older systems, especially those who are gradually losing grandfathered pipe to increases in DOT class location."

The industry has been put on notice. Stricter enforcement will affect many pipeline systems lacking adequate information, and the result will be significant. Many legacy systems installed prior to 1970 will "feel the pinch," he says.

"Back in the 1950s, nobody knew any better in terms of how carefully records had to be kept. Sophisticated inventory-management systems were not available, and sometimes detailed information on individual joints of pipe was not collected. In addition, as these systems changed hands—in some cases, several times in the intervening 40-some years —some of the information was lost."

Assessment methods

Thorleifson envisions that pipeline operators across the U.S. are now busily scouring their records. If the records are not available, hydrostatic-pressure testing could be necessary. For large-diameter pipelines, such testing can be very expensive.

Why not rely on pigging to help determine pipe properties? In many cases, the pipelines lacking adequate documentation were built before smart-pigging was available. Therefore, the lines are not designed to accept smart pigs.

"Smart-pig tools are usually fairly long. Many older pipelines have bends or other features that these tools cannot negotiate. There is no way to run the pig through the way the lines are currently configured. So pressure-testing is going to be the only viable alternative."

When smart pigs came into vogue, regulators urged operators to run smart pigs through older lines, but found that was often not an option. Direct-assessment methods were developed as an alternative. PG&E had performed direct assessment on the San Bruno pipeline, but the direct-assessment methods selected were based on corrosion being the primary threat. The direct assessment was not intended to detect seam problems.

In its advisory, PHMSA encourages operators to be especially aware of all potential threats of concern when designing their integrity-management (IM) programs, noting, "Some operators are not sufficiently aware of their pipeline attributes nor are they adequately or consistently assessing threats and risks as a part of their IM programs. Over the past several years, PHMSA inspections and investigations have revealed deficiencies in individual operators' risk-analysis approaches, the integration of data into these risk assessments, the abilities to adequately support the selection of assessment methods, identification and implementation of preventive and mitigative measures, and maintenance of up-to-date risk information and findings about their pipeline segments."

While it is unknown how many miles of pipeline in the U.S. may be affected by records problems, Thorleifson believes the number of miles may be significant, especially in eastern U.S. systems where older pipe predominates.

For gas-transmission pipelines, MAOP can be determined in three basic ways. One method is to calculate design-pressure, where, if an operator knows all of the components of his pipeline, the operator can calculate the MAOP upper limit.

Such components include specified minimum yield strength, wall thickness, diameter and design factor, which is determined by the Department of Transportation's class location and other factors. In general, the higher the class location, the lower the MAOP. Another component is the longitudinal joint factor, which is based on the seam type.

"There is also a temperature de-rating factor," adds Thorleifson. "Gas coming out of a compressor station is hot, and heats up the pipe. So there is a de-rating factor based on that as well."

The second method to determine MAOP is to use pressure-test information. The third option relies on historic operating pressures, using the highest operating pressure recorded in the five years prior to July 1, 1971. The lowest MAOP yielded by the three methods prevails. However, the historic operating pressure limitation can be overridden by performing a pressure test or via the uprating process.

Goodbye grandfather

According to the gas transmission MAOP rules, if any design characteristic is unknown, including pressure ratings for fittings that are attached to the main line, an operator cannot rely on the design pressure to determine MAOP. If pressure test and historic operating pressure data are likewise unreliable, the operator must undertake a pressure test.

"As grandfathered pipe goes away due to increases in DOT class location, some operators are likely to encounter problems with records," he says. "A lot of these pipelines will have to be pressure tested."

There are several kinds of pressure tests. Various standards organizations have determined that such testing does not significantly damage the pipe. Admittedly, if there is a failure during the test, a repair will be required. But, generally, pressure tests are designed to be within current design limits, so pipelines in good condition are not damaged during the procedure.

Push back

While the thought of pressure testing large, legacy transmission systems, could, at some point, become prohibitively expensive, Thorleifson has not heard of much push back from operators. The industry appears to be taking a wait-and-see attitude.

"Operators will want to wait to see how things shake out with PG&E," Thorleifson predicts. "But if I were a betting man, I would bet that folks who are operating these older systems are going to be looking hard at their records right now."

If the lack of sufficient documentation of older pipelines becomes a significant issue, operators can negotiate with regulatory agencies to find a safe and reliable compromise.

"Right now, PHMSA is conducting prolonged and extremely thorough audits. Improperly maintained records are not going to pass muster," Thorleifson warns.