API 598
Valve Inspection and Testing
Inspection, examination and pressure testing of valves
What it covers
- Shell test, backseat test and seat test requirements
- Test pressures relative to the valve rating
- Minimum test durations by valve size
- Allowable seat leakage rates by valve type and seat material
- Which tests are mandatory and which are optional
- Test fluid requirements
What it does not cover
- NDE of the castings or forgings, which comes from the material specification and the project requirements
- Functional or endurance testing
- Fugitive emission testing - that is ISO 15848
- In-service testing after installation
This section exists because standards are routinely listed on valve datasheets in positions where they do not apply. Knowing the boundary is what makes the reference useful.
Allowable leakage is not zero
API 598 gives allowable seat leakage rates that depend on valve type, size and seat material. Metal-seated valves have a non-zero allowance; resilient-seated valves are required to show no visible leakage. Any supplier claiming zero leakage on a metal-seated high-temperature valve is either quoting a different standard or is not being precise. State the leakage class you need and it can be tested and reported against.
Test duration scales with size
Minimum test durations increase with valve size, because a larger seating area needs longer to reveal a leak. Short-cutting the duration is one of the easier ways for a supplier to pass a test that should have failed, which is why witness points on the test are worth having.
MSS SP-61 as the alternative
Some specifications call up MSS SP-61 instead. The test philosophy is similar but the allowable rates and durations differ. What matters is that one is chosen and stated on the ITP, rather than the valve being tested to whichever is easier to pass.
How we report it
The test scheme applied is stated on the ITP before manufacture, and the test report records the actual pressures, durations and observed leakage - not just a pass mark.
Products this applies to
Verify it yourself
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