Buyers often place “API 598 / ISO 5208” in one cell as if the slash means either standard produces the same test. That creates ambiguity at the test bench. Choose the governing route and write deviations or supplementary requirements separately.
01 / Scope
Begin with the product standard and contract hierarchy.
ISO 5208 states that it is intended to work with the specific requirements of a valve product standard and that the product standard takes precedence where requirements differ. That is a useful procurement principle even when another test standard is selected: identify the design/product standard first, then the inspection and test standard.
API 598 is widely used for valve inspection and testing in API/ASME purchasing routes. The exact applicability, test set and acceptance requirements depend on the valve type, size, class and edition.
| Decision | API 598 route | ISO 5208 route |
|---|---|---|
| Primary reference | API inspection/testing standard and applicable API/ASME product standard. | ISO pressure-testing standard plus applicable product standard. |
| Leakage language | Use the categories and acceptance basis in the ordered edition. | Use the rate/designation and conditions in the ordered edition. |
| Certificate | State API 598 edition and individual test results. | State ISO 5208 edition and the specified leakage rate/conditions. |
| Project additions | List separately and resolve conflicts. | List separately and resolve conflicts. |
02 / Test set
A shell test and a closure test answer different questions.
The shell test examines the pressure boundary under the defined production-test condition. Closure testing examines leakage past the closed obturator and seating system. A backseat test applies only where the valve design includes the feature and the governing requirements call for it.
Do not accept one overall “PASS” line when the order calls for several tests. Each result should identify medium, pressure, duration, direction where relevant, acceptance criterion and actual observation or measured leakage.
03 / Configuration
Pressure direction and cavity condition belong in the procedure.
A floating ball valve, trunnion ball valve, gate valve and check valve do not present the same pressure paths. Seats can be unidirectional or bidirectional. Double-isolation arrangements can create cavity-pressure questions. The approved procedure should show how the specific design is filled, vented, pressurized and examined.
For check valves, state whether the test pressure is applied in the reverse direction and how leakage is collected or observed. For bidirectional isolation claims, require evidence for the required directions rather than relying on a generic seat-test statement.
04 / Report
The report should be reproducible by someone who was not at the test.
Tie the report to the valve serial number, purchase order, approved drawing and procedure revision. Include calibrated gauge or transducer IDs and ranges. Record operator, QA acceptance and purchaser or third-party witness status.
When a valve fails and is repaired, the final certificate should not erase the event. The nonconformance, repair authorization, repeated examination and successful retest should remain traceable.
- IdentitySerial number, tag, size, class, material and valve type.
- AuthorityProduct standard, test standard, editions and project specification.
- ConditionMedium, pressure, time, temperature where relevant and direction.
- AcceptancePermitted leakage and actual result for every required test.
- EquipmentInstrument ID, range and calibration validity.
- HistoryWitness status, repair, nonconformance and retest references.
05 / RFQ
Write one controlling route and make exceptions visible.
Avoid “API 598/ISO 5208 latest”. State the selected standard and edition, then specify any additional low-pressure gas closure test, purchaser witness, chart recording or special leakage requirement. Ask the supplier to list conflicts before order placement.
If the end user accepts either route, request two clearly identified offers or require the supplier to name the proposed route. Do not wait until final inspection to discover which acceptance table was used.
Production pressure testing shall comply with [standard and edition]. The supplier shall submit the test procedure and a serial-number-specific report showing each required shell, backseat and closure test, pressure direction, acceptance criterion, actual result and calibrated instrument IDs.
Sources / editorial control
Source basis
- ISO 5208:2015. Official scope; confirmed current in 2025.
- API Standards Plan. Official API source used to verify publication status; licensed API 598 text remains controlling.
- MSS SP-61. Official MSS pressure-testing publication page for an additional recognized route.
Review limit: This is a procurement comparison, not a substitute for API 598, ISO 5208 or the applicable product standard. Exact test values must be taken from licensed copies.