Integripedia Topic
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.
Related Topics
- API 560 - Fired Heaters for General Refinery Service
- API 579-1/ASME FFS-1 - Fitness-For-Service (FFS)
- API 594 - Check Valves: Flanged, Lug, Wafer, and Butt-Welding
- API 620 - Design and Construction of Large, Welded, Low-Pressure Storage Tanks
- API 650 - Welded Tanks for Oil Storage
- API 660 - Shell-and-Tube Heat Exchangers
- API 661 - Petroleum, Petrochemical, and Natural Gas Industries Air-Cooled Heat Exchangers
- API RP 1173 - Pipeline Safety Management Systems
- API RP 1176 - Assessment and Management of Cracking in Pipelines
- API RP 538 - Industrial Fired Boilers for General Refinery and Petrochemical Service
- API RP 571 - Damage Mechanisms Affecting Fixed Equipment in the Refining Industry
- API RP 572 - Inspection of Pressure Vessels
- API RP 573 - Inspection of Fired Boilers and Heaters
- API RP 574 - Inspection Practices for Piping System Components
- API RP 575 - Inspection Practices for Atmospheric and Low Pressure Storage Tanks
- API RP 576 - Inspection of Pressure-Relieving Devices
- API RP 577 - Welding Processes, Inspection, and Metallurgy
- API RP 578 - Material Verification for New and Existing Alloy Piping
- API RP 580 - Risk Based Inspection (RBI)
- API RP 581 - Risk Based Inspection Technology
- API RP 583 - Corrosion Under Insulation and Fireproofing
- API RP 584 - Integrity Operating Windows
- API RP 585 - Pressure Equipment Integrity Incident Investigation
- API RP 651 - Cathodic Protection of Aboveground Petroleum Storage Tanks
- API RP 75 - Safety and Environmental Management System for Offshore Operations
- API RP 751 - Safe Operation of Hydrofluoric Acid Alkylation Units
- API RP 754 - Process Safety Performance Indicators for the Refining and Petrochemical Industries
- API RP 934 - Materials and Fabrication of Heavy Wall Pressure Vessels for High-Pressure Hydrogen Ser
- API RP 939-C - Guidelines for Avoiding Sulfidation (Sulfidic) Corrosion Failures in Oil Refineries
- API RP 970 - Corrosion Control Documents
- International Organization for Standardization (ISO)
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
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.
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.
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.
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.
A summary of some of the important topics that were discussed at the API Fall Refining and Equipment Standards Meeting in Atlanta.
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...
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.
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.
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...
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.
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.
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...
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....
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.
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...
This primer covers the fundamentals of High Temperature Hydrogen Attack (HTHA). Download and learn about this serious damage mechanism.
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.