Coating, Corrosion Led to AZ Pipeline Explosion
According to an investigation report from the National Transportation Safety Board, a fatal natural gas pipeline explosion in Arizona from 2021 resulted from tented tape wrap, leading to stress corrosion cracking.
The NTSB also found during its investigation that owner and operator Kinder Morgan, Inc., did not record the correct coating type used for the segment of the pipeline, which led to a risk assessment that did not identify the cracking or corrosion.
On August 15, 2021, just before 5:30 a.m., a 30-inch-diameter natural gas transmission pipeline ruptured in Coolidge, Arizona. According to the NTSB, the rupture resulted in the releasee of natural gas vapor that ignited and exploded, causing a blast wave and gas-fed fire.
The incident reportedly destroyed a farmhouse about 451 feet away, killing two occupants and seriously injuring a third. Additionally, about 33 acres of vegetation were damaged in some areas about 878 feet away from the rupture crater.
A 47-foot segment of pipe was also ejected about 133 feet from the center of the crater. Kinder Morgan estimated property damage and emergency response costs to be $5,541,740.
An Arizona pipeline explosion caused death and destruction. Here's what sparked it https://t.co/rPpW7vz064— azcentral (@azcentral) May 2, 2023
The Arizona Republic reports that the company said it has replaced the ruptured pipe with new pipe, conducted multiple pipeline integrity tests, revised and enhanced its risk models for stress corrosion cracking and taken other actions.
The pipeline was originally installed in 1986 by All-American Pipeline Co. to carry crude oil from west to east. It was converted to natural gas transmission in 2002 and 2003, also altering the flow from east to west. Kinder Morgan took the pipeline over in 2012.
Data from Pipeline Examination Reports listed the coating type for the pipeline segment was listed as fusion-bonded epoxy. These were integrated into a Pipeline Open Database Standard (PODS), or Kinder Morgan’s internal data management tool to identify and document pipeline specifications.
The NTSB reports that one pipeline data report, submitted in 2011 after a composite sleeve was installed on Line 2000 approximately 375 feet from the rupture location, noted that the coating type listed as fusion-bonded epoxy was incorrect at that location and that the actual coating type was spiral wrap tape. However, this was not recorded in the PODS.
At the time of the rupture, Kinder Morgan reportedly used a risk assessment to evaluate the pipeline segment for threats. The risk assessment algorithm determined the probability of failure from stress corrosion cracking near neutral and high pH SCC, the two types of SCC defined in ASME B31.8S.
This was also further calculated using several correlating factors recording in PODS, including:
Before the rupture, the coating type of the ruptured pipeline segment was incorrectly listed in PODS as fusion-bonded epoxy. However, the coating type was spiral wrap tape. As a result, Kinder Morgan did not identify threats of SCC on the ruptured pipeline segment.
The investigation found that cracks leading to the rupture formed and coalesced on the outside of the pipe near a seam weld. The board noted that spiral wrap tape is more vulnerable to the type of corrosion that damaged the pipe compared to fusion-bonded epoxy or a powder coating.
“The National Transportation Safety Board determines that the probable cause of the August 15, 2021, pipeline rupture in Coolidge, Arizona, was tented tape wrap leading to stress corrosion cracking, a fracture at a longitudinal seam weld, and subsequent rupture of the pipe,” wrote the NTSB in its report.
“Contributing to the rupture was Kinder Morgan’s failure to record the correct coating type used for this segment of pipeline, leading to a risk assessment that did not fully identify the risk of stress corrosion cracking.”
The full investigation report can be found here.