scope:

This best practice report complements API RP 934-A and specifies additional fabrication considerations that should be observed when constructing a new heavy wall pressure vessel using vanadium-modified Cr-Mo materials intended for hydrogen service at elevated temperature and pressure. It applies to vessels that are designed, fabricated, certified, and documented in accordance with ASME Boiler and Pressure Vessel Code (BPVC), Section VIII, Division 2, including paragraph 3.4 of the ASME Code, Supplemental Requirements for Cr-Mo Steels and former ASME Code Case 2151, as applicable (or equivalent international codes).

Nominal material chemical compositions covered by this report are the vanadium-modified steels including 2¹/₄Cr-1Mo −2¹/₄V, 3Cr- 1Mo-¹/₄V-Ti-B, and 3Cr-1Mo-¹/₄V-Nb-Ca steels. The interior surfaces of these vessels may have an austenitic stainless steel cladding or weld overlay to provide additional corrosion resistance.