Energy Industry: Energy Artery
October 12, 2017
To celebrate Exponent's 50th Anniversary, we created a book featuring our most notable projects from the last decade. Below is an example of our work in the Energy Industry.

Energy Artery: Analyzing how the San Francisco Peninsula lost a third of its natural gas supply in a single explosive tragedy.

On September 9, 2010, a 30-inch diameter natural gas transmission pipeline (Line 132) owned and operated by Pacific Gas & Electric Company (PG&E) ruptured in a residential area in San Bruno, California, just south of San Francisco. Line 132 was one of three local gas transmission lines that serviced the San Francisco Peninsula. Shortly after the rupture an explosion occurred, creating a gaping crater roughly the size of a tennis court.

The explosion and fire destroyed 38 homes and damaged 70. Eight fatalities and numerous injuries and damage resulted from the explosion and fire. A pipe segment about 28 feet long was blown 100 feet from the crater.

Exponent was retained by PG&E to perform a root cause analysis of the accident, examining records of operations and physical assets of Line 132; pipe specifications; gas flow data; pressure readings; historical purchase orders; interviews and testimony regarding the accident and third-party reports; and our own metallurgical analysis of the Line 132 pipe and specimens collected by the National Transportation Safety Board (NTSB). Line 132 was installed in 1956 with a missing weld and a ductile tear that was most likely created during a post-installation pressure test. Over the next 44 years, the fatigue crack that developed grew to a critical size when subjected to cyclic loading associated with pressure changes during operation.

Exponent’s conclusion: no single factor led to the rupture — a unique combination of structural and metallurgical factors precipitated the tragedy.