New MAOP Leeway Pretty Narrow

By Stephen Barlas, Washington Editor | December 2008 Vol. 63 No. 12

But there is probably not going to be much of a rush to take advantage of the new MAOP ceiling. According to Boss, the two biggest shortcomings in the final rule have to do with construction specifications for new steel pipelines and the time lines for fixing anomalies which are discovered after in line inspection of existing pipeline. With regard to the latter, PHMSA in the final rule sets two categories of anomalies: the first having to be repaired immediately, the second within one year. Anomalies are sorted into the two categories based on a “conservative” view of their risk based on a pig inspection. “We think the time frames are unduly conservative, and don’t have a good technical basis,” says Boss.

PHMSA has already used those conservative criteria in Corrective Action Orders (CAO), the most recent one issued to Transco. In that case, a leak near Appomattox, VA, on Sept. 14, 2008, resulted in an explosion which destroyed two homes and caused multiple injuries. The CAO PHMSA issued to Williams’ Transco unit listed five pages of exacting requirements that Transco would have to meet for a section of its Gulf of Mexico to New York pipeline running through Virginia. Those have to be met immediately, and were imposed without prior notice or a hearing.

PHMSA seems intent, according to Boss, on applying those same type of exacting anomaly repair criteria not just to CAOs and pipelines uprating under the new MAOP rule, but to all pipelines operating in high consequence areas. That was the direction PHMSA indicated it was heading at a workshop it held on Oct. 22.

The centerpiece of the PHMSA workshop was a report by Advantica, a consulting company, which looked at the standard assessment methods used by the pipeline industry. Advantica concluded that failure predictions on pipe with real corrosion defects were shown to be conservative using the ASME B31G, Modified ASME B31G and RSTRENG methods. Failure predictions were, in the argot of the report, “non conservative” where defects were greater than 40 percent of the pipe wall and in line pipe of grade X52 and above.

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