API 598 standard comprehensively covers various types of valves such as gate valves, globe valves, plug valves, ball valves, check valves, and butterfly valves with elastic seats, non-metallic seats (such as ceramics), and metal metal seats. Among them, the elastic valve seat includes: a) a soft valve seat, which contains solid and semi-solid lubricating grease types (such as lubricating plug valves); b) Soft and metal combination valve seat (such as laminated valve seat ring); c) Any other valve seat material designed to meet the elastic valve seat leakage rate specified in Table 5. This standard not only supplements other API standards that reference it, but also applies to other types of valves in the event of an agreement between the buyer and the valve manufacturer.
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Required Tests of API 598 Valve
| Valve Type | Shell Test | Backseat Test | Low-Pressure Closure | High-Pressure Closure |
| Gate Valve | Required | Required | Required | Optional (1) |
| Globe Valve | Required | Required | Required | Optional (1) |
| Check Valve | Required | N/A | Optional | Required |
| Ball Valve | Required | N/A | Required | Optional (1) |
| Butterfly Valve | Required | N/A | Required | Optional (1) |
| Plug Valve | Required | N/A | Required | Optional (1) |
(1) Note: For soft-seated (resilient) valves, high-pressure closure testing is typically required to verify seat sealing performance.
Test Pressures of API 598 Valve
| Test Item | Test Medium | Test Pressure |
| Shell Test | Liquid (Typically Water) |
≥1.5×≥1.5× Cold Working Pressure (CWP) |
| Backseat Test | Liquid (Typically Water) |
≥1.1×≥1.1× Cold Working Pressure (CWP) |
| High-Pressure Closure (Seat) | Liquid (Typically Water) |
≥1.1×≥1.1× Cold Working Pressure (CWP) |
| Low-Pressure Closure (Seat) | Gas (Air or Nitrogen) | 60 psi ~ 100 psi (4~7 bar) |
- CWP (Cold Working Pressure): This refers to the maximum pressure at which a valve is allowed to operate at ambient temperature (usually -29°C to 38°C).
- Shell Test Duration: The valve must be partially open during this test to ensure the body, bonnet, and gaskets are fully pressurized.
- Zero Leakage Requirement: For Soft-Seated (Resilient) valves, API 598 strictly mandates zero visible leakage during both the high-pressure and low-pressure closure tests.
- Seat Testing: High-pressure tests are excellent for structural seat integrity, while low-pressure gas tests are more sensitive at detecting microscopic scratches on the sealing surfaces.
API 598 Minimum Test Durations (Seconds)
| Valve Size (NPS) | DN (mm) | Shell Test (sec) | Backseat Test (sec) | Closure Test (sec) |
|
≤≤ 2" |
50 | 15 | 15 | 15 |
| 2 ½" to 6" | 65 to 150 | 60 | 60 | 60 |
| 8" to 12" | 200 to 300 | 120 | 120 | 120 |
|
≥≥ 14" |
350+ | 300 | 300 | 300 |
API 598 Maximum Allowable Leakage (Liquid Test)
| Valve Size (NPS) | Soft-Seated Valves | Metal-Seated Valves (Gate/Globe/Ball) |
|
≤≤ 2" |
0 Drops | 0 Drops (Standard depending on type) |
| 2 ½" to 6" | 0 Drops | 12 Drops per Minute |
| 8" to 12" | 0 Drops | 20 Drops per Minute |
|
≥≥ 14" |
0 Drops | 2 Drops per Inch of Diameter / Minute |
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FAQ
What is the difference between API 598 and API 600?
API 600 covers steel gate valves, API 6D covers pipeline valves, and API 598 covers valve inspection and testing. Product data for API-rated items must include the applicable standard as an attribute to ensure correct specification and procurement.
What is the difference between API 598 and API 609?
API 609 is a specification for butterfly valves with lug-type and wafer-type configurations designed for installation between ANSI B16 flanges, 150 to 1500 class. API 598 covers the testing and inspection requirements for check, gate, globe, ball, plug & butterfly valves. Steel valve pressure ratings in ASME/ANSI B16.