What is the differences between API 6D vs API 594?
Valve standards from API - the American Petroleum Institute: *
API SPEC 6D
Specification for Pipeline Valves. API Specification 6D is an
adoption of ISO 14313: 1999, Petroleum and Natural Gas
Industries-Pipeline Transportation Systems-Pipeline Valves. This
International Standard specifies requirements and gives
recommendations for the design, manufacturing, testing and
documentation of ball, check, gate and plug valves for application
in pipeline systems. * ANSI/API 600
Bolted Bonnet Steel Gate Valves for Petroleum and Natural Gas
Industries - Modified National Adoption of ISO 10434:1998.