API 6D and API 598 core differences are mainly reflected in the following aspects:
1. Standard Positioning and Coverage
API 6D
is a comprehensive specification for the design, manufacture, assembly and testing of pipeline valves in the oil and gas industry, with special focus on the whole process requirements for valves for mainline pipelines (e.g. ball valves, gate valves, check valves, etc.).
The 25th edition expands the scope of application to other areas outside the oil and gas industry, and adds a new guidance appendix on valve repair, modification and non-standard design.
API 598
focuses on the valve inspection and pressure test methods, belonging to the generality of the test standard, applicable to a variety of industrial valves (including, but not limited to, the valves covered by API 6D).
2. The difference between the test requirements
test medium
API 6D: default to fresh water or light oil as the test medium, only at the request of the customer to carry out low/high pressure gas sealing test.
API 598: according to the type of valve and pressure level, the flexibility to use high-pressure liquid or low-pressure gas sealing test.
Test time and method
Shell hydrostatic pressure test: API 6D requires 30 minutes for valves DN ≥ 20, while API 598 requires only 1-2 minutes.
Gas test: API 6D uses nitrogen with helium leak detector, API 598 uses air.
Supplementary test
API 6D will carry out additional valve seat test when explicitly requested by the user, while API 598 has no such requirement.
3. The application of scenarios and mandatory API
6D is mainly
used in oil and gas pipelines, direct burial welded ball valves and other high-pressure or safety-critical scenarios, in line with the U.S. federal regulations (such as BSEE, PHMSA) of the mandatory reference requirements.
The new edition (25th edition) has mandatory references to API 6DX actuator standard with enhanced bolting and design verification requirements.
API 598
as a general test standard for all types of industrial valves factory inspection, especially for non-oil and gas field of conventional valve acceptance.
4. Code Evolution and Industry Impact
API 6D has been continuously updated since its release in 1936, expanding from mainline pipeline valves to industry-wide applications, while API 598 maintains its position as the basic test standard.
API 6D is more demanding for manufacturers, covering details such as Quality Specification Levels (QSLs) and deep-cooling of materials, while API 598 focuses more on uniformity of testing processes.
In summary, API 6D is the core specification for the whole life cycle management of valves in the oil and gas industry, while API 598 is the benchmark method for general valve testing, and there are significant differences between the two in terms of application scenarios, test details and industry mandatory.
