A report released Monday said the pipeline ruptured due to external corrosion of the pipe wall. The corrosion was caused by deteriorated coating and ineffective cathodic protection on the outside of the pipe.
The second failure was a lack of detection of the corrosion. The line which ruptured and subsequently exploded had not been inspected since 1988.
According to the NTSB the rock back-fill used to bury the line damaged the outer coating of the pipe and contributed to the problem.
The explosion happened December 11, 2012 at 12:41p.m. Investigators said 20-feet of pipe in the line separated and was blown out of the ground. High pressure gas escaping from the line ignited immediately causing and explosion and fireball.
The fire damage was 820-feet wide and extended nearly 1,100 feet along the pipeline right-of-way. Three nearby houses were destroyed and several more damaged. Nobody was killed or seriously injured in the incident. Officials say 76 million cubic feet of natural gas escaped and burned in the incident.
The Safety Board’s report suggested the disaster was intensified by the inadequate warning system Columbia Gas Transmission had in place. Investigators said the lack of adequate data and supervisory control caused a delay in shutting off gas to the area and allowed the fire to burn much longer.
The report indicated a 2009 inspection of two other lines nearby showed corrosion in the pipe. However, the discovery did not prompt an inspection of the line in question when mitigation efforts were considered.
The NTSB investigating team offered recommendations in their analysis for the Pipeline and Hazardous Material Administration to add principal arterial roadways and interstates, freeways, and expressways to a list of ”identified sites” listed as “highly consequential.” The ensuing fire burned more than 800 feet of I-77 in both directions.
The report recommended to Columbia Natural Gas to implement a process to select alert setpoints and adequately train operators on what to do if they are set off. It also called for a modified supervisory control and data acquisition system which will allow an operator to know the moment there is a breach, fire, or explosion. Finally it called for the use of all data collected on all pipelines in area of high consequence to be used in risk assessment for all pipelines on a single region.
