This best practice report complements API 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 Code Section VIII, Division 2, including Paragraph 3.4 of the ASME Code, Supplemental Requirements for Cr-Mo Steels and ASME Code Case 2151, as applicable (or equivalent international codes).

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