The American Petroleum Institute (API) specification 6D defines the requirements for design, manufacturing, and testing of axial, ball, check, gate, and plug valves. In the United States, it is referenced by the Bureau of Safety and Environmental Enforcement (BSEE) in the Code of Federal Regulations (CFR); the Pipeline and Hazardous Materials Safety Administration (PHMSA); and by state regulators. The specification is also widely referenced by regulators across the globe.
Learn more about API 6D here.