API STD 934-C : 2026

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.

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.

This standard applies to new fabrication of heavy-wall pressure vessels in petroleum refining, petrochemical, and chemical facilities in which hydrogen or hydrogen-containing fluids are processed at elevated temperature and pressure. It is based on decades of industry operating experience and the results of experimentation and testing conducted by independent manufacturers, fabricators, and purchasers of heavy-wall pressure vessels for this service.

Licensors and owners of process units in which these heavy-wall pressure vessels are to be used may modify or supplement this standard with additional proprietary requirements.