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

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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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