30 C.F.R. § 250.834
Use of USVs
You must install, maintain, inspect, repair, and test any valve designated as the primary USV in accordance with this subpart, your DWOP (as specified in §§ 250.286 through 250.295), and API Standard 6AV2 (incorporated by reference, see § 250.198). For additional USV testing requirements, refer to § 250.880.