API 6D, 600, 602, 6A: oil and gas valve standards

API 6D covers ball valves, gate valves, plug valves and check valves for use in pipeline systems transporting natural gas, natural gas liquids, liquid petroleum products and other hydrocarbons. It is the dominant standard for valves used on onshore and offshore transmission pipelines and on gathering systems.

API 6D specifies requirements for design, materials, dimensions, testing, marking and documentation. Shell test, seat test and backseat test pressures are higher than their EN equivalents, and the documentation requirements (including material traceability and hydrostatic test records for each individual valve) are more demanding. API 6D valves must be hydrostatically tested at the factory — no statistical sampling.

ISO 14313 is the international equivalent of API 6D and is technically identical. Projects outside the US often specify ISO 14313 rather than API 6D, but the requirements are the same. An API 6D monogram on a valve indicates that the valve was manufactured under the API Quality Management System and meets the API 6D requirements.

API 600 covers bolted-bonnet steel gate valves for petroleum and natural gas industries, in sizes NPS 1/2 (DN15) through NPS 24 (DN600). It specifies wall thickness (more conservative than EN standards), minimum bore dimensions, pressure-temperature ratings, stem design and testing requirements. API 600 valves are standard for refinery isolation service and wherever the heavier wall thickness and conservative design of the API standard is required.

API 602 covers compact steel gate valves in smaller bores (NPS 1/2 to NPS 4, DN15 to DN100) and includes both bolted-bonnet and pressure-seal designs. API 602 is used for instrument isolation, chemical injection and small-bore process isolation in refinery and petrochemical applications.

API 600 and API 602 gate valves are more expensive than their EN equivalents because of the additional material and wall thickness requirements, but the difference is usually justified in high-pressure or high-temperature refinery service where the margin of safety matters.

API 6A applies to valves, wellheads, Christmas trees and related equipment used at the surface of oil and gas wells. It covers pressure ratings from 2,000 psi (138 bar) to 20,000 psi (1380 bar) and temperature classes from sub-zero (Class L, to -75°F) through high temperature (Class V, to 350°F).

API 6A is a significantly more demanding standard than API 6D or API 600 in terms of material qualification, non-destructive examination and pressure testing. All API 6A equipment must carry API monogram marking and must be manufactured under an API-licenced quality management system. The standard applies to gate valves, ball valves, check valves and choke valves used in wellhead service.

For procurement purposes: API 6A equipment requires a longer lead time than pipeline or refinery valves, reflects more extensive factory testing in the price, and requires a much more detailed data package (including full material certifications, NDE records and pressure test records) for project handover.

API 607 defines the fire-test requirements for quarter-turn and other soft-seated valves (ball, plug, butterfly) used in refinery and petrochemical applications. A valve that has passed API 607 testing has demonstrated that, after exposure to a defined fire scenario, it still provides an acceptable level of shutoff when the seat has been damaged or destroyed by heat.

API 6FA applies the same fire-test philosophy to valves already meeting API 6D or API 6A. A valve with API 6FA certification is suitable for pipeline service where fire-safe closure is required.

ISO 10497 is the international equivalent of API 607 for quarter-turn valves and covers the same fire-test scenario. EN 1366-4 covers fire-testing for valves used in building fire protection systems, which is a different standard for a different duty. Ensure you are specifying the correct fire-test standard for your application.

API valves are generally heavier, more conservatively designed and more extensively tested than their EN equivalents. The additional cost reflects the more demanding material, design and testing requirements rather than simply brand premium. For applications where the API standard is not contractually required, an EN-compliant valve of the same size, material and pressure class will perform equivalently in most services.

The choice between API and EN is often driven by the operator's engineering standards rather than by the valve duty. Operators using US or international oil company engineering standards typically specify API; EU-based operators using EN process piping standards typically specify EN. Both are valid approaches; the key is consistency throughout the project.