A couple of days ago US media reported interim results of investigation into the failure in Mayflower, Arkansas that I have mentioned previously here and here. Quoting in full the statement send by ExxonMobil to media (with highlighting added):
ExxonMobil Pipeline Company (EMPCo) and the Pipeline and Hazardous Materials Safety Administration (PHMSA) have received the results of an independent assessment conducted by Hurst Metallurgical Research Laboratory, Inc. on the Pegasus Pipeline segment that failed on March 29, 2013. We are currently in the process of reviewing and analyzing the data. Based on the metallurgical analysis, the independent laboratory concluded that the root cause of the failure can be attributed to original manufacturing defects – namely hook cracks near the seam. Additional contributing factors include atypical pipe properties, such as extremely low impact toughness and elongation properties across the ERW seam. There are no findings that indicate internal or external corrosion contributed to the failure. While we now know the root cause of the failure, we are still conducting supplemental testing, which will help us understand all factors associated with the pipe failure and allow for the verification of the integrity of the Pegasus Pipeline. These tests will help us determine the mitigation steps we need to take to ensure a similar incident does not occur again.
Although the pipe was many decades old, and manufactured by a process no longer used, this does illustrate why the industry remains obsessive about pipe quality.