Inspectioneering

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

Explore this topic

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.  

Related Topics

Relevant Links

Topic Tools

Share this Topic

Contribute to Definition

We welcome updates to this Integripedia definition from the Inspectioneering community. Click the link below to submit any recommended changes for Inspectioneering's team of editors to review.

Contribute to Definition
Articles about API RP 941 - Steels for Hydrogen Service at Elevated Temperatures and Pressures
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
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
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
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.

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
Partner Content

InVista is a lightweight, hand-held ultrasonic in-line inspection tool (intelligent pig) capable of detecting pipeline wall loss and corrosion in unpiggable or difficult-to-inspect pipelines. The pipeline geometry inspection data captured by the...

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
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
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...

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.

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
Partner Content

What do you need: CONSULTING - Subject matter experts, consultants, or team of highly skilled engineers to help solve my problem. SOFTWARE - My team requires software, products, or resources that will solve the problem. TRAINING - I require...

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
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.

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
    Downloads & Resources related to API RP 941 - Steels for Hydrogen Service at Elevated Temperatures and Pressures
      News related to API RP 941 - Steels for Hydrogen Service at Elevated Temperatures and Pressures
        Partner Content

        Becht’s industry-leading Corrosion and Metallurgical experts are here to help with significant owner-operator experience covering the refining, petrochemical and chemical industries. This expertise is leveraged to help our clients become more...


        Inspectioneering Journal

        Explore over 20 years of articles written by our team of subject matter experts.

        Company Directory

        Find relevant products, services, and technologies.

        Talent Solutions

        Discover job opportunities that match your skillset.

        Case Studies

        Learn from the experience of others in the industry.

        Integripedia

        Inspectioneering's index of mechanical integrity topics – built by you.

        Industry News

        Stay up-to-date with the latest inspection and asset integrity management news.

        Blog

        Read short articles and insights authored by industry experts.

        Expert Interviews

        Inspectioneering's archive of interviews with industry subject matter experts.

        Event Calendar

        Find upcoming conferences, training sessions, online events, and more.

        Downloads

        Downloadable eBooks, Asset Intelligence Reports, checklists, white papers, and more.

        Videos

        Watch educational and informative videos directly related to your profession.

        Acronyms

        Commonly used asset integrity management and inspection acronyms.