Guideline on Remedial Actions for HYCO Plant Components Subject to High Temperature Hydrogen Attack

February 14, 2023

High temperature hydrogen attack (HTHA) is a mechanism that can significantly weaken and damage a variety of steel materials, including carbon steel and various low alloy steels, that are used in the construction of hydrogen plants. Equipment operated in the HTHA concern zone becomes more susceptible to damage over time and requires regular examination.

In 2010, an HTHA-induced catastrophic failure of a heat exchanger at a Tesoro refinery in Anacortes, Washington, United States resulted in the deaths of seven employees. This tragic event led to an investigation by the United States Chemical Safety and Hazard Investigation Board (CSB) and subsequently a revision of API RP 941, Steels for Hydrogen Service at Elevated Temperatures and Pressures in Petroleum Refineries and Petrochemical Plants. That revision included a change to the HTHA limits, known as the Nelson Curves, which are used to determine the maximum operating temperature and pressure for carbon and low alloy steels in hydrogen-rich service.  Based on the revisions made to API RP 941, CGA has identified this API document as the Recognized and Generally Accepted Good Engineering Practice for assessing HTHA risk.

Given the API RP 941 revised Nelson Curves, carbon steel might no longer be considered an appropriate material in certain services in HYCO plants. Operational HYCO plants need to be aware that the design criteria for carbon steel and other low alloy steels in hydrogen-rich service have changed.

CGA H-16 provides:

  • Guidance and some examples of methodologies for the review of existing HYCO plant assets to determine their potential for HTHA-initiated cumulative damage.
  • Guidelines for risk categorization, inspection strategies, and recommendations on risk mitigation.
  • Actions for the owners and operators of HYCO plants in response to the updated guidance on the HTHA mechanism documented in API RP 941.

Click here to download/purchase CGA H-16.