API RP 934-C

Abstract

This standard covers materials and fabrication requirements for new 1¼Cr-½Mo steel heavy-wall pressure vessels and heat exchangers for high-temperature, high-pressure hydrogen service. It applies to pressure 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 standard, “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. At shell or head thicknesses greater than 4 in. (100 mm), 1¼Cr-½Mo plates and forgings have been shown to have difficulty meeting the toughness requirements given in this document. Meeting the specified properties can be especially difficult with thick 1¼Cr-½Mo forgings, such as integrally reinforced nozzles, flanges, tube sheets, channel covers, etc. 2¼Cr-1Mo vessel components can be used as an alternative to ensure mechanical properties can be achieved. Although outside of its scope, this document can be used as a resource for pressure vessels below 2 in. (50 mm) in shell thickness, with changes defined by the purchaser. Multilayer pressure vessels are outside the scope of this document. This standard is not intended for use for equipment operating above 825 °F (440 °C) or in the creep range. API Standard 934-E covers these higher-temperature applications.