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

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

API RP 941, Steels for Hydrogen Service at Elevated Temperatures and Pressures in Petroleum Refineries and Petrochemical Plants, is a recommended practice developed and published by the American Petroleum Institute (API). This RP is intended to help owner-operators 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. API RP 941 was originally published in 1997, and the most recent 8th Edition was published in February of 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. The guidelines in this RP can also be applied to hydrogenation plants such as those that manufacture ammonia, methanol, edible oils, or higher alcohols.

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 lower temperatures, hydrogen enters the steel due an electrochemical mechanism, which operates under different principles. Furthermore, this RP only covers HTHA resistance for steels operating within the recommended guidelines. Other damage mechanisms or corrosives present in the process stream, as well as potential damage caused by rapid cooling of the metal after it has been removed from high temperature, high-pressure hydrogen service, can still be a problem and must be properly managed to prevent mechanical integrity issues.

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

Breakthroughs in Predictive HTHA Life Assessment: Time Dependent Nelson Curves and Inspection Planning Enhancements

January/February 2022 Inspectioneering Journal

This article describes HTHA predictive modeling advances that are designed to demonstrate a direct integration with inspection such that modeling and inspection can be leveraged together in a way never done before.

Authors: Dave Dewees, P.E., Gerrit Buchheim, P.E.

Into the Grain - Advancements in HTHA Detection Methods - Part 1

May/June 2021 Inspectioneering Journal

Hydrogen-induced damage mechanisms have been studied endlessly, leading to changes in equipment design and development of new inspection practices. However, the highly localized nature and difficulty of detection of HTHA add additional complexities.

Authors: Jose Aparicio

Reynolds Wrap Up: Highlights from the API Subcommittee on Inspection and Mechanical Integrity (SCIMI) at the Fall 2020 Standards Meeting

Blog

A summary of some of the important topics that were discussed at the API Fall 2020 Refining and Equipment Standards Meeting that was held via virtual conferencing.

Authors: John Reynolds

Reynolds Wrap Up: Highlights from the API Subcommittee on Inspection and Mechanical Integrity (SCIMI) at the Spring 2020 Standards Meeting

Blog

A summary of some of the important topics that were discussed at the API Spring Refining and Equipment Standards Meeting that was held via virtual conferencing.

Authors: John Reynolds

Practical HTHA Experience and Time-Based Nelson Curves for Improved Equipment Life Management

March/April 2020 Inspectioneering Journal

Nelson curves, which are the foundation of the industry’s HTHA programs, can be tied to mechanistic models from several sources, allowing the recreation of Nelson curves for different operational histories and time durations.

Authors: Dave Dewees, P.E., Gerrit Buchheim, P.E., Jeremy Staats, P.E., Charles Becht V, P.E.

Global, simultaneous inspection with Acoustic Emission Testing

Partner Content

AET is a powerful, non-intrusive inspection technique to verify the structural integrity of pressure vessels, spheres, high-temperature reactors and piping, coke drums, above-ground storage tanks, cryogenic storage tanks, and more.

Reynolds Wrap Up: Highlights from the API Subcommittee on Inspection and Mechanical Integrity (SCIMI) Meetings at the Fall 2019 API Standards Meeting

Blog

A summary of some of the important topics that were discussed at the API Fall Refining and Equipment Standards Meeting in Atlanta.

Authors: John Reynolds

Reynolds Wrap Up: Highlights from the API Subcommittee on Inspection and Mechanical Integrity (SCIMI) Meetings at the Spring 2019 API Standards Meeting

Blog

A summary of some of the important topics that were discussed at the Spring Meeting, including the recently-held API Inspection and Mechanical Integrity Summit, subcommittee activities, and progress with the API Individual Certification Program.

Authors: John Reynolds

Reynolds Wrap Up: Highlights from the API Subcommittee on Inspection and Mechanical Integrity (SCIMI) Meetings at the Fall 2018 API Standards Meeting

Blog

A quick summary of some of the important topics that were discussed at the Fall Meeting, including the upcoming API Inspection and Mechanical Integrity Summit, subcommittee activities, and progress with the API Individual Certification Program.

Authors: John Reynolds

HTHA Inspection Detection Confidence Improves Basis for New API Recommendations

September/October 2018 Inspectioneering Journal

This article discusses the advances in NDE that have given owners increased confidence on how to assess equipment integrity in HTHA service providing risk prioritization of equipment as well as providing the ability to make more reliable...

Authors: Michael Nugent, Timothy Armitt

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

This article provides 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 along with challenges they have encountered.

Authors: Gerrit Buchheim, P.E.

Maximize the value of your data to improve inspection through CML Prioritization

Partner Content

Statistical techniques are meant to complement the work of SMEs and can provide deeper insights into the inspection data collected as part of a reliability program. Pinnacle has combined traditional methods, expertise, and Machine Learning to...

Some Resources to Learn More about Preventing High Temperature Hydrogen Attack (HTHA)

Blog

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.

Authors: Jeremiah Wooten

Avoiding HTHA Failures in Existing Equipment

November/December 2010 Inspectioneering Journal

High Temperature Hydrogen Attack (HTHA) is a long known and still occurring degradation issue for fixed equipment construction materials in the hydrocarbon process industry where hydroprocess plants (hydrogen plus hydrocarbons) are in service....

Authors: John Reynolds

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.

99 Diseases of Pressure Equipment: High Temperature Hydrogen Attack (HTHA)

January/February 2005 Inspectioneering Journal

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...

Authors: John Reynolds