MSS SP-61

Covers — shell (body) and seat closure pressure testing of valves, giving test pressures, durations, and acceptance leakage for gate, globe, check, ball, plug, and butterfly valves.

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 alternate refinery testing regime → API 598.

SP-61 and API 598 are parallel test standards; the project specification picks one.

SP-61 sets minimum requirements for factory valve testing:

• Shell Test — hydrostatic test at a multiple of the rating to prove the pressure boundary is leak-tight.
• Seat Test — closure test at a defined pressure with allowable leakage that differs for metal versus resilient seats.
• Acceptance — pass/fail leakage limits and hold durations; documentation of results.

MSS SP-61 defines how valves are pressure-tested before shipment: a shell test that proves the body pressure boundary and a seat test that proves closure tightness. Test pressures are derived from the valve's B16.34 rating, and the allowable seat leakage depends on whether the seat is metal or resilient.

It is the common alternative to API 598 for general-service and MSS-standard valves. Because the two standards differ in detail, the datasheet must name which one applies.

Engineering Note: For critical isolation, verify that the specified seat-leakage class is tight enough — the default allowable leakage for metal seats is not zero.