This recommended practice (RP) covers materials and fabrication requirements for new 1¼Cr-Mo steel heavy wall pressure vessels and heat exchangers for high-temperature, high-pressure hydrogen service. It applies to vessels that are designed, fabricated, certified, and documented in accordance with ASME Section VIII, Division 1 or Division 2. This document may also be used as a resource for equipment fabricated of 1Cr-½Mo Steel. This document may also be used as a resource when planning to modify an existing heavy wall pressure vessel.
The interior surfaces of these heavy wall pressure vessels may have an austenitic stainless steel or ferritic stainless steel weld overlay or cladding to provide additional corrosion resistance.
For this recommended practice, "heavy wall" is defined as a shell thickness 2 in. (50 mm) or greater, but less than or equal to 4 in. (100 mm) at the time of mill heat treatment.
Although outside of its scope, this document can be used as a resource for vessels down to 1 in. (25 mm) or lower in shell thickness, with changes defined by the Purchaser.
Multilayer vessels are outside the scope of this document. Likewise, this recommended practice is not intended for use for equipment operating above 825 °F (440 °C) or in the creep range. API RP 934-E covers these higher temperature applications.