NTSB Faults 54-Year-Old Welds in San Bruno Blast
The board concluded Aug. 30 that the gas release resulted from welds made in 1956 on short pipeline sections that did not meet generally accepted industry practice or welding standards then in effect.
The National Transportation Safety Board concluded Aug. 30 that a gas transmission pipeline leaked in September 2010 in San Bruno, Calif., resulting in a massive explosion and fire, because welds done on five short pipe sections in 1956 were inadequate. The fracture originated in the partially welded longitudinal seam of one of six short pipe sections because the sections "would not have met generally accepted industry quality control and welding standards then in effect, indicating that those standards were either overlooked or ignored," the board found. It concluded the weld defect in that section would have been visible when it was installed, and a sewer line installation in 2008 near the rupture did not damage the defective pipe.
The final report ruled out seismic activity, corrosion, direct third-party damage, or drug use by workers at the Milpitas Terminal.
It said the emergency response by the city of San Bruno was prompt and appropriate, but it took Pacific Gas and Electric (PG&E) 95 minutes to stop the flow of gas and isolate the rupture site. This response time "was excessively long and contributed to the extent and severity of property damage and increased the life-threatening risks to the residents and emergency responders," NTSB said.
The board said PG&E lacks a detailed and comprehensive procedure for responding to large-scale emergencies such as a transmission pipeline break, "including a defined command structure that clearly assigns a single point of leadership and allocates specific duties to supervisory control and data acquisition staff and other involved employees. PG&E's supervisory control and data acquisition system limitations caused delays in pinpointing the location of the break. The use of either automatic shutoff valves or remote control valves would have reduced the amount of time taken to stop the flow of gas," it said.
The report concluded the internal line pressure preceding the rupture did not exceed PG&E's maximum allowable operating pressure for that line and would not have posed a safety hazard for a properly constructed pipe. In addition, if grandfathering of older pipelines had not been permitted since 1961 by the California Public Utilities Commission and since 1970 by the U.S. Department of Transportation, this transmission line "would have undergone a hydrostatic pressure test that would likely have exposed the defective pipe that led to this accident," it stated.
PG&E has taken several actions to shore up public and regulatory confidence in its operations, in the wake of the explosion. It hired Anthony F. Earley, Jr., 62, as chairman, CEO, and president on August 8 and filed a multi-year modernization plan Aug. 26 with the California Public Utilities Commission; the company says the plan will make its nearly 6,000-mile natural gas transmission pipeline system one of the safest in the country.
The plan includes:
- Strength testing all pipe segments that have not been previously strength tested (including those previously exempted by federal regulations), replacing segments that should be replaced, and retrofitting pipelines to allow internal inspections, or "pigging"
- Enhancing electronic monitoring of the gas system to identify operational issues and prevent or quickly locate pipeline ruptures
- Expanding the use of automated valves to isolate and minimize damage if any pipeline rupture does occur
- Transitioning away from traditional paper records and consolidating all gas transmission pipeline data into an integrated electronic data management system to strengthen system operations, maintenance, inspections, and regulatory compliance
"This plan represents a clear break with the way PG&E and other gas utilities once approached pipeline safety," said Nick Stavropoulos, executive vice president of gas operations for PG&E. "Under the CPUC's leadership, with PG&E's full support, the state has taken lessons learned from several independent investigations of the San Bruno tragedy and adopted new standards to help ensure that such an accident never happens again. Our multi-year plan to test, verify, and upgrade the integrity of our gas transmission pipelines will meet those rigorous standards and help California lead the natural gas industry in pipeline safety."
Earley is the first chief executive of PG&E to come from outside the organization. He previously headed Michigan-based DTE Energy and built its core businesses -– Detroit Edison and Michigan Consolidated Gas Company -– into two of the most highly respected electric and natural gas operating companies, with strong performance on many of the industry's key safety and reliability measures, accorrding to PG&E.