In This Article
- 1.What Makes a Valve Cryogenic?
- 2.Extended-Stem (Cold-Box) Design
- 3.Low-Temperature Material Qualification
- 4.Seat and Seal Materials
- 5.Cryogenic Testing Requirements
- 6.Valve Types for LNG Service
- 7.LNG Project Valve Specifications
What Makes a Valve Cryogenic?
A cryogenic valve is specifically designed, tested, and certified for reliable operation at temperatures below -46 degrees C, with the most demanding applications reaching -196 degrees C for liquid nitrogen and liquid oxygen and -162 degrees C for LNG at atmospheric pressure. Standard industrial valves are not suitable because carbon steel becomes brittle, elastomeric seals harden and crack, and conventional stem packing loses its sealing ability as the packing bore ices up with atmospheric moisture.
Extended-Stem (Cold-Box) Design
The defining feature of a cryogenic valve is the extended bonnet, also called a cold-box extension or cold stem. This extended neck keeps the packing gland and actuator at or close to ambient temperature, even when the valve body is immersed in liquid cryogen. The extended length is calculated to create a sufficient temperature gradient so that ice formation and packing damage in the gland area are prevented. Typical extension lengths range from 150 mm for LPG service at -50 degrees C to 600 mm or more for liquid helium at -269 degrees C.
Low-Temperature Material Qualification
| Material | Min. Temperature | Charpy Impact Test Temp | Application |
|---|---|---|---|
| 304/316 Austenitic Stainless Steel | -196 C | -196 C (no ductile-brittle transition) | LNG, LPG, liquid N2, liquid O2 |
| ASTM A352 LCB (Carbon Steel) | -46 C | -46 C (20 J minimum) | LPG, propane, ethylene |
| ASTM A352 LC3 (3.5% Ni Steel) | -101 C | -101 C (20 J minimum) | Ethylene, LPG at sub-ambient |
| 9% Nickel Steel (ASTM A553) | -196 C | -196 C (34 J minimum) | LNG storage, primary containment |
| Aluminium Alloy (5083) | -196 C | Not required (FCC crystal, ductile) | LNG tanks, aluminium valve bodies |
| Hastelloy C-276 | -196 C | -196 C | Cryogenic corrosive service |
Seat and Seal Materials
Elastomeric seats based on NBR, EPDM, or neoprene are unsuitable for cryogenic service as they become glass-hard and fracture below -40 degrees C. Acceptable seat and seal materials include PTFE (usable to -200 degrees C), PCTFE (usable to -200 degrees C, preferred for oxygen service due to lower oxygen reactivity than PTFE), ultra-high-molecular-weight polyethylene (UHMWPE), and metal-to-metal seats in 316 SS or Stellite overlay for fire-safe and highest reliability applications. For liquid oxygen, all non-metallic materials must pass oxygen compatibility testing per ASTM G63 and G88.
Cryogenic Testing Requirements
- BS 6364 (UK/International): the primary standard for cryogenic valves — specifies cold functional test at service temperature, shell and seat leakage at -196 degrees C, and cycling requirements
- API 6D Annex F: cryogenic qualification testing for pipeline valves in LNG service
- ASME B16.34: pressure-temperature ratings at cryogenic temperatures with separate tables for austenitic and low-alloy materials
- Shell MESC SPE 77/300: extended-stem design and testing for Shell LNG projects
- Cold functional test: valve must open and close smoothly after cold-soak at design temperature with internal cryogenic medium
- External leakage test: packing gland must be leak-free (0.001 sccs helium maximum) at cryogenic temperature
- Thermal cycling: typically 5 cycles from ambient to design temperature to verify no fatigue cracking
Valve Types for LNG Service
| Valve Type | LNG Application | Key Design Feature |
|---|---|---|
| Cryogenic Ball Valve | LNG transfer lines, loading arms, storage tank outlets | Extended stem, PTFE seats, trunnion-mounted for large bore |
| Cryogenic Gate Valve | Large-bore main isolation, storage tank nozzle valves | Extended bonnet, OS&Y, bolted bonnet for easy maintenance |
| Cryogenic Globe Valve | Throttling in LNG vaporisers, flow control on send-out | Extended bonnet, PTFE packing, metal seat for fire-safe |
| Cryogenic Butterfly Valve | Low-pressure LNG lines, vapour recovery systems | Triple-offset design, metal seat, cryogenic-rated PTFE |
| Cryogenic Check Valve | Anti-reverse flow on pumps, compressors, vapour lines | Spring-assisted swing or nozzle type with SS internals |
| Safety Relief Valve (SRV) | LNG tank overpressure protection, boil-off gas lines | Stainless steel spring and disc, set pressure per ASME VIII Div.1 |
LNG Project Valve Specifications
Major LNG projects specify cryogenic valves to BS 6364 or API 6D Annex F with full PMI (positive material identification), radiographic or UT inspection of pressure-containing welds, and cold functional testing witnessed by third-party inspectors from Lloyd's, Bureau Veritas, or DNV. Extended stems are sized to maintain the packing above 0 degrees C in normal operating conditions. For safety-critical isolation duties, double-block-and-bleed (DBB) cryogenic ball valves with cavity vent are specified to prevent thermal expansion lock-up of trapped cryogenic liquid.
Request Cryogenic Valve Quotation
API 6D certified. Ships worldwide. 24-hour quote response.
Need industrial valves for your project?
API 6D, ASME B16.34 certified. 120+ cities served. 24-hour quote response.