API 598

Covers — inspection, examination, supplementary examinations, and pressure testing (shell, backseat, and seat) for resilient-, nonmetallic-, and metal-seated gate, globe, plug, ball, check, and butterfly valves, with allowable seat-leakage rates by type.

Does NOT cover (exclusions) — the following are governed elsewhere:

• Pressure-temperature ratings that set the test pressure → ASME B16.34.
• Fire-type qualification → API 607 / API 6FA.
• The alternative general/MSS test regime → MSS SP-61; pipeline valve testing detail → API 6D.

API 598 is the test/acceptance layer invoked by the API product-valve standards.

API 598 sets minimum requirements for factory valve inspection and testing:

• Shell Test — hydrostatic test of the assembled valve body proving the pressure boundary.
• Backseat Test — where applicable, verifies the stem backseat.
• Seat (closure) Test — proves closure tightness at defined pressure; allowable leakage varies by seat type (metal permitted small leakage; resilient typically zero).
• Examination — visual and, where specified, supplementary NDE; documentation of results.

API 598 specifies the inspection, examination, and pressure testing that valves must pass before shipment. It defines three main tests: the shell (body) test proving the pressure boundary, the backseat test (where applicable), and the seat (closure) test proving tightness.

The standard sets allowable seat leakage rates that vary by valve type and seat material — metal-seated valves are permitted a small leakage, while resilient (soft) seats are typically required to be zero leakage. Test pressures are derived from the valve's B16.34 rating.

Engineering Note: Procurement datasheets usually cite "testing per API 598." Confirm whether a stricter seat-leakage class is required for critical isolation.