In This Article
- 1.BS 6364 Test Sequence
- 2.Extended Bonnet Requirements
- 3.Impact Testing — ASTM A370 at −196°C
- 4.Acceptance Criteria Summary
BS 6364 (Valves for Cryogenic Service) is the British Standard (also widely adopted internationally) governing valve design, materials, and testing for service below −29°C. It applies to LNG (−162°C), liquid oxygen (−183°C), liquid nitrogen (−196°C), liquid argon (−186°C), liquid propylene (−47°C), and liquid ethylene (−104°C) applications.
BS 6364 Test Sequence
- 1Ambient temperature shell pressure test (1.5× rated pressure, 100% of production) — verifies body integrity before cryogenic test
- 2Ambient temperature seat leak test (1.1× rated pressure) — baseline seat leakage
- 3Cool-down test: submerge valve in liquid nitrogen (−196°C) while closed; monitor for external leakage
- 4Cryogenic seat test (1.1× rated pressure at −196°C): valve closed in LN₂; measure seat leakage — must meet Rate A per EN 12266 (zero detectable for Class A applications)
- 5Cryogenic operational test: valve cycled open/closed 3 times while submerged in LN₂; must operate smoothly (no binding or seizure)
- 6Return to ambient: warm valve slowly; re-check shell and seat integrity after thermal cycling
Extended Bonnet Requirements
BS 6364 mandates an extended bonnet (also called a cold bonnet) for all valves operating below −29°C. The bonnet extension length must be sufficient to ensure that the gland packing and actuator remain above the cryogenic zone — typically 350 mm minimum for −196°C service (longer for larger-diameter valves or insulated piping systems). The purpose: prevent ice formation at the gland seal (which would cause leakage) and keep elastomeric actuator components above brittle fracture temperature.
Impact Testing — ASTM A370 at −196°C
All metallic components forming the pressure boundary of a BS 6364 valve must pass Charpy V-notch impact testing at the minimum design temperature. For −196°C service (LN₂, LOX, LAR): minimum 27 J absorbed energy at −196°C per ASTM A370. A182 F316L (austenitic stainless steel) inherently retains toughness to −269°C — no impact testing concern. Carbon steel (A105, WCB) fails below −46°C and MUST NOT be used for cryogenic service.
Acceptance Criteria Summary
| Test | Standard | Acceptance Criterion |
|---|---|---|
| Shell test | EN 12266 / API 598 | No visible leakage through body wall or joints |
| Seat test (ambient) | EN 12266 Rate A | Zero leakage for Class A; 0.18 ml/min per inch for Class B |
| Cryogenic seat test | BS 6364 / EN 12266 | Rate A (zero detectable) for LOX, LNG, LIN |
| Operational test at −196°C | BS 6364 Clause 5 | 3 full open/close cycles without binding |
| Impact test | ASTM A370 | ≥ 27 J at test temperature for each specimen |
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