Inspectioneering Journal

High Temperature Hydrogen Attack (HTHA) Likely Cause of Explosion

This article appears in the November/December 2010 issue of Inspectioneering Journal.

Per a report in Downstream Today, by Whitney Pipkin Skagit Valley Herald, Mount Vernon, Knight Ridder/Tribune Business News on August 30, 2010, “Tesoro Anacortes Refinery announced Friday what investigators determined was the likely cause of an April 2 blast that killed seven workers.”

The article went on to say, “Testing of the damaged heat exchanger at an Ohio lab revealed that a chain of events called a high temperature hydrogen attack caused the fire, Tesoro investigators found.

They believe hydrogen molecules worked their way over time into small imperfections in the steel casing of the heat exchanger. The hydrogen then reacted with carbon in the steel, forming bubbles of methane. Those bubbles led to cracks in the steel, causing it eventually to give way.”

This is a very important topic for operators of certain oil and gas refineries, chemical and petrochemical facilities and power plants as millions, perhaps billions of dollars of equipment operate in service environments that may produce susceptibility to this type of attack.

Some but not all, things to consider regarding equipment in this service:

  • HTHA is a time dependent phenomena (time in service, made of certain materials and fabrication practices, exposed to certain conditions, etc.)
  • Prediction of the likelihood of attack considers important variables such as, but not limited to, materials of construction (including weld metal, base material, cladding or overlay type and quality), hydrogen partial pressure, temperature, external stresses and more
  • How well and how specifically are conditions monitored for equipment
  • Unstable carbides can exist in highly localized places and can be the breeding ground for this type of attack (very important when developing an equipment reliability strategy, including inspection)
  • The classic reference for decisions regarding equipment in HTHA service is API’s RP 941 STEELS FOR HYDROGEN SERVICE AT ELEVATED TEMPERATURES AND PRESSURES IN PETROLEUM REFINERIES AND PETROCHEMICAL PLANTS (for more information on this document visit the web site
  • Additional information can be found from sources such as previous Inspectioneering Journal articles including the “99 Diseases of Pressure Equipment” series and “Methods for Detection, Characterization & Quantification of High Temperature Hydrogen Attack”, the Welding Research Council (see article in this issue, especially the “Hydrogen Series” of articles), the Materials Properties Council’s* joint industry project, MolyHy - For more information visit the web site

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