A statistical analysis of reportable hazardous liquid and natural gas pipeline accidents/incidents in the U.S. from January 2010 to January 2021 was conducted by evaluating releases reported to be caused by external corrosion. The US Department of Transportation's Pipeline and Hazardous Materials Safety Administration (PHMSA) Office of Pipeline Safety (OPS) Accident Investigation Division (AID) collected historical records from Form PHMSA F 7000-1 (Hazardous Liquid/CO2 Accident Report) and Form PHMSA F 7100.2 (Gas Transmission and Gathering Systems Incident Report) for the 11-year period. Since January 2010, 358 of the 4,332 (8%) hazardous liquid accidents; and 122 of the 1,364 (9%) natural gas incidents involved failures due to external corrosion. These failures were reported as corrosion failures under section G1: Corrosion Failure, and 29 accidents were reported as environmental cracking-related accidents in section G5: Material Failure of Pipe or Weld of PHMSA's accident/incident reports.

The total property damage for these failures accounted for $1.2 billion and 133,000 barrels of unintentional hazardous liquid released; and $94 million and 3,000 MMcf of unintentional natural gas released. There were two ignitions, two explosions, one injury, and one fatality associated with hazardous liquid accidents. Likewise, there were 23 ignitions, 14 explosions, three injuries, and no fatalities from natural gas incidents. Soil was contaminated in 236 accidents, wildlife was impacted in 14 accidents, and water was contaminated in 62 accidents. Common causes of external corrosion accidents/incidents involved galvanic corrosion, atmospheric corrosion, stray current, microbiologically influenced corrosion (MIC), selective seam corrosion, stress corrosion cracking (SCC), sulfide stress cracking (SSC), hydrogen stress cracking and other, which can be associated with uniform corrosion, pitting corrosion, crevice corrosion, corrosion under insulation (CUI), metal loss, oxidation, pH, disbonded coating, aqueous corrosion, and corrosion fatigue.

In this paper, several cases will be showcased to highlight the contributing causes and underlying mechanisms of corrosion damage of components that resulted in significant releases of hazardous substances onto operator's property, rights-of-way, and the environment. The objectives of this paper are to understand the causes of the failures and their consequences, to identify the risk factors involved, to discuss mitigative measures after failure, and to observe trends that may indicate the need for additional preventative and mitigative actions. The over-riding goal is to provide details in areas for potential improvement in pipeline operations to reduce risk and improve integrity management.

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