API RP 941 - Steels for Hydrogen Service at Elevated Temperatures and Pressures

Last update: Jan 16, 2017

API RP 941, Steels for Hydrogen Service at Elevated Temperatures and Pressures in Petroleum Refineries and Petrochemical Plants, Eighth Edition, is a recommended practice developed and published by the American Petroleum Institute (API). This RP is intended to help identify and manage equipment potentially subject to high temperature hydrogen attack (HTHA) by putting into place practical operating limits for carbon and low alloy steels in hydrogen service at elevated temperatures and pressures. This RP also discusses how the resistance of steels to hydrogen damage can be affected by high stress, heat treating, chemical composition, and cladding. A summary of inspection methods to evaluate equipment for the presence of HTHA is also included. The first edition of the recommended practice was originally published in January 1997, and the most recent release is the eighth edition, published in February 2016.

API RP 941 applies to any equipment in refineries, petrochemical facilities, chemical facilities, or hydrogenation plants that happen to operate in environments in which hydrogen-containing fluids are processed at elevated temperatures and pressures. Hydrogenation plants can include any in which the manufacturing of ammonia, methanol, edible oils, or higher alcohols takes place.
API RP 941 only covers equipment that runs at high temperatures and does not cover any equipment that runs at below 400°F (204°C). At those temperatures, hydrogen enters the steel due an electrochemical mechanism, which operates under different principles. Likewise, this RP only applies to HTHA thus, even when following the guidelines listed in this RP, steel might not necessarily resist other damage mechanisms in a process stream. It also doesn’t cover damage that might be caused due to rapid cooling of the metal that might occur after it has been removed from high temperature, high-pressure hydrogen service.

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Steels for Hydrogen Service at Elevated Temperatures and Pressures in Petroleum Refineries and Petrochemical Plants
November/December 2010 Inspectioneering Journal

The following references are from the American Petroleum Institute. They are widely used in the petroleum refining and petrochemical industries for managing equipment in HTHA service and are available in the public domain.

A New Method for Prioritizing Equipment in HTHA Service for Inspection & Replacement and the Challenges in Obtaining Process Conditions to be Used in the HTHA Assessment
November/December 2014 Inspectioneering Journal
By Gerrit M. Buchheim, P.E. at Becht Engineering Co., Inc.

High Temperature Hydrogen Attack (HTHA) is a complex damage mechanism that continues to defy investigators trying to make predictions on the anticipated degree of damage or service life. This article provides some background on HTHA, discusses some current developments in HTHA inspection and mitigation, and describes how one Refiner is instituting an HTHA risk management plan for its refineries and the challenges and pitfalls they have encountered.

March 3, 2014 By Greg Alvarado at Inspectioneering Journal

The following question was posed by a member of the Inspectioneering Community: I am working in a fertilizer plant and our inspection team is very new. I was wondering if professionals in similar plants could share their knowledge related to inspection work. Please elaborate on details about the inspection function, as well as the main subjects we should focus on.

Avoiding HTHA Failures: An Owner-User Perspective of the HTHA Risk Mitigation Process: Part II
January/February 2014 Inspectioneering Journal
By Mike Urzendowski at Valero Energy

The intent of these two articles is to share lessons learned from recent experiences setting up a comprehensive HTHA review process across multiple refineries, and to help other operators define and mitigate the HTHA risk to an acceptable level.

January 20, 2014

Last week we mentioned three important tips to consider when addressing high temperature hydrogen attack (HTHA). This week, we'd like to provide the reader with a few helpful resources that deal with the topic of HTHA.

November/December 2013 Inspectioneering Journal
By Mike Urzendowski at Valero Energy

A recent High Temperature Hydrogen Attack (HTHA) failure atarefineryinthestateofWashingtonwasa“wakeupcall” to our industry. On April 2, 2010, the shell of a feed-effluent heat exchanger in the Naphtha Hydrotreating (NHT) unit at the Tesoro Anacortes WA refinery ruptured, ultimately resulting in seven fatalities.

Solutions for Your Facility Inspection Data Management Needs
Partner Content

Owners and operators of complex equipment and facilities need tools to manage the life of their assets. Rigorous inspection is needed to minimize the risk of equipment failure and meet regulatory requirements. It is critical to know...

January/February 2005 Inspectioneering Journal
By John Reynolds at Intertek

HTHA falls into multiple categories of corrosion mechanisms, including environmentally assisted cracking, hydrogen assisted cracking, and high temperature degradation. Sometimes HTHA is confused with low temperature hydrogen cracking mechanisms that result from hydrogen being driven into steels by aqueous corrosion reactions.