Federal and state authorities last week turned up the heat in parallel but separate investigations and reviews of the Sept. 9 San Bruno natural gas transmission pipeline explosion and fire, and the utility in the middle, Pacific Gas and Electric Co. (PG&E), moved ahead with stepped up pipeline safety checks and operating/maintenance plans.

With the advent of the winter heating season, state officials and PG&E were mindful that the pipeline that failed is still operating at reduced pressure and will need to be returned to more normal levels when cold weather hits.

A preliminary report from the National Transportation Safety Board (NTSB) concluded that a power glitch at PG&E’s natural gas terminal in Milpitas, CA, opened up a pipeline control valve that in turn caused a surge in pressure minutes before the San Bruno, CA, gas pipeline ruptured last month (see NGI, Sept. 13). The ruptured pipeline was fractured length-wise and at welds that held the pipe sections together, but the report did not mention corrosion. The thickness of the pipe’s walls was described in the report as “fairly uniform.”

Line 132, a 30-inch diameter line that runs from the Milpitas terminal through the East Bay, was running at a maximum operating pressure of 375 pounds per square inch (psi) on Sept. 9, the day of the blast, the report stated. The maximum allowable operating pressure was 400 psi.

According to the report, a PG&E crew was dispatched to shut down the pipeline 34 minutes after the blast, and it took an hour and a half from the moment the line ruptured to completely shut it down, the board said. At 11:30 p.m. the utility isolated the gas distribution system and within a minute “fires from escaping natural gas at damaged houses went out.”

In the lead-up to the explosion, NTSB investigators found that when a PG&E crew was working on an uninterruptible power supply (UPS), the gas pipeline’s computer control system malfunctioned. Electrical power to the system fell, which caused the control valve to open and pressure to build in the line. The report said “instead of supplying a predetermined output of 24 volts of direct current, the UPS system supplied approximately 7 volts or less to the SCADA [supervisory control and data acquisition] system. Because of this anomaly, the electronic signal to the regulating valve for Line 132 was lost. The loss of the electrical signal resulted in the regulating valve moving from partially open to the full open position as designed.”

Pressure in the pipeline following the malfunction increased to 386 psi, and a pneumatically activated valve maintained the pressure at that level, the NTSB report stated. At about 5:45 p.m., the system was recording a pressure of more than 375 psi at another station in Daly City, CA. The pressure continued rising until it reached about 390 psi at around 6 p.m., said investigators.

Eight minutes later pressure dropped to 386 psi, and at 6:11 p.m., when the San Bruno explosion occurred, pipeline pressure had fallen to 361.4 psi. A minute later pressure stood at 289.9 psi.

An investigation is continuing concerning fractures in the pipeline and the pipe’s metal strength, the NTSB said. An electron microscope analysis of the ruptured pipe segment also is being conducted.

In response, PG&E said last Wednesday the NTSB investigation has still not “gotten to the bottom” of the explosion and fire, and the San Francisco-based combination utility pledged to continue to support the investigation.

“Although a final report and a conclusive set of findings are likely to be many months down the road, this initial release of information is an essential first step,” said PG&E utility President Chris Johns. “We welcome and appreciate the painstaking efforts of the NTSB experts to conduct a thorough and comprehensive investigation to determine the root cause of this terrible accident.”

The American Gas Association (AGA) echoed PG&E’s reaction, noting that “important facts” have now been brought out in the preliminary report but “additional testing still needs to be done.” The Washington, DC-based trade group for the distribution side of the gas industry said it was “eager” to learn the root cause of the incident.

In another sliver of information emerging from the investigation, PG&E may appear more culpable, and in its response to the NTSB report the utility again “pledged” to customers and government officials to “operate our infrastructure safely and securely,” adding that the company intends “to take any and all appropriate steps to ensure we’re meeting this fundamental commitment.”

Separately, Northwest Natural Gas Co. director for gas supply Randy Friedman told an industry meeting in Los Angeles Wednesday that he thinks the San Bruno tragedy could have a major impact on capital spending in the industry on pipeline maintenance and safety programs.”I think the San Bruno explosion will have incredible impacts on the industry in terms of cost and assuring the integrity of our pipelines. That’s going to be on the radar, and there could be legislation that impacts costs and operations.”

PG&E reiterated that it has re-inspected the three major transmission pipelines that serve the San Francisco Peninsula, and it is in the process of conducting aerial inspections and ground leak surveys of its entire gas transmission system. Although under fire for allegedly holding back information, the utility again said it will “take steps” to share more information about the gas pipeline system with public officials, emergency personnel and customers.

“We continue to extend our support and our sympathies to the San Bruno community and the residential affected by this tragedy,” Johns said.

Also last week, PG&E announced a five-part, multi-year effort to greatly strengthen the safety and reliability of its natural gas transmission pipeline system. Called Pipeline 2020, the program will augment initiatives implemented by the combination utility in the wake of the Sept. 9 pipeline tragedy.

In consultation with regulators and various industry experts, Johns said the utility will undertake a modernization initiative on key transmission pipeline segments located in heavily populated and other critical areas. A third-party expert will be used to make the review and assessment with the goal of making sure that all critical lines can accommodate state-of-the-art inspections, including internal “pigging” technologies.

Following the latest PG&E and NTSB announcements, the California Public Utilities Commission (CPUC) created an independent review panel selected by CPUC President Michael Peevey and confirmed by the full five-member commission last Thursday. It is empowered to gather facts and make recommendations “based on the facts to the CPUC as to whether there is a need for the general improvement of the safety of PG&E’s gas transmission pipeline system” (see NGI, Sept. 27). Named to the panel were:

In the aftermath of the pipeline failure, the CPUC ordered PG&E to lower the pressure in the affected 30-inch diameter transmission pipeline by 20%, but with winter approaching the regulators want the panel’s judgment as to when to order the operating pressures to be raised to their normal levels (about 370 pounds per square inch).

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