Download the API RP 934-A:2025 PDF | Material Selection and Fabrication for 2¼Cr-1Mo, 2¼Cr-1Mo-¼V, 3Cr-1Mo, and 3Cr-1Mo-¼V Steel Heavy-duty Pressure Vessels Designed for High-Temperature, High-Pressure Hydrogen Environments.
The present Recommended Practice addresses the specifications for the materials and construction of new heavy-duty pressure vessels made from 2¼Cr and 3Cr steel, intended for use in high-temperature and high-pressure hydrogen service. A “heavy-wall” vessel is characterized by a shell thickness of 4 inches (100 mm) or more, while “high-temperature” refers to operational temperatures ranging from 650 °F (345°C) to the maximum design temperature, as defined by ASME Section II-D:2023 Table 5A for the material’s time-dependent properties, in accordance with API 941 guidelines.
While not directly applicable, this RP can serve as a reference for pressure vessels with wall thicknesses under 4 inches (100 mm), those operating at temperatures below 650 °F (345°C), or those with maximum design temperatures exceeding the specified limits, with any modifications to be agreed upon by the buyer. The document can also be utilized in the planning stages for the modification of an existing heavy-duty pressure vessel.
For applications requiring significantly higher pressures, beyond the scope of hydroprocessing, ASME Section VIII, Division 3 is the standard to follow. A dedicated ASME Code Case has been created for these alloys within Division 3. Division 3 imposes more stringent design criteria, including the necessity for fatigue and fracture mechanics analyses, as well as more rigorous material testing standards. The application of these regulations is not within the purview of this document.