Prevention of Valve Freezing and Seizure in Cryogenic Storage Tanks

Cryogenic storage tanks, containing liquids such as LNG, liquid nitrogen, or liquid oxygen, rely on valves for controlled filling, withdrawal, and safety operations. Valve freezing or seizure due to extreme low temperatures can lead to operational disruption, safety hazards, and increased maintenance costs. Implementing proper preventive measures is crucial to ensure reliable tank operation.

1. Causes of Valve Freezing

Cryogenic Temperatures: Extremely low liquid temperatures can cause thermal contraction of valve components, leading to sticking or binding.

Moisture Ingress: Water vapor or residual moisture in the valve body can freeze, creating ice formation that prevents proper movement.

Improper Material Selection: Valves made from materials with low ductility at cryogenic temperatures are more prone to fracture or jamming.

Condensation and Frosting: Condensation on valve surfaces can freeze during low-temperature operation, impeding valve movement.

2. Preventive Measures

Material Selection:

Use materials compatible with cryogenic temperatures, such as stainless steel or nickel alloys, which retain ductility and mechanical strength.

Avoid materials prone to embrittlement at low temperatures.

Valve Design:

Employ valves specifically designed for cryogenic service, featuring extended bonnets, low-friction seats, and minimal dead space to reduce ice formation.

Consider ball valves or gate valves with cryogenic-rated components for critical applications.

Drying and Purging:

Ensure valves and pipelines are free of moisture before commissioning.

Purge with dry gas to remove residual moisture before operation.

Insulation and Heat Tracing:

Insulate valve bodies and piping to reduce heat loss and frost formation.

Use low-power heat tracing on critical valves to maintain operable temperatures.

Regular Operation and Maintenance:

Cycle valves periodically to prevent sticking.

Inspect and clean valves, seats, and stems for frost or ice buildup during routine maintenance.

Operational Controls:

Avoid sudden depressurization or rapid flow changes that can induce localized freezing.

Monitor temperature and pressure near valves to detect abnormal conditions early.

Conclusion
Valve freezing and seizure in cryogenic storage tanks can be effectively prevented through proper material selection, cryogenic-specific valve design, moisture control, insulation, and regular maintenance. Proactive measures ensure reliable valve operation, maintain safety, and enhance the operational lifespan of cryogenic storage systems.

References

EN 14620 – Design and Manufacture of Cryogenic Vessels.

NFPA 55 – Compressed Gases and Cryogenic Fluids Code.

Barron, R.F. (1999). Cryogenic Systems, 2nd Edition. CRC Press.

Bratt, R., & Mort, P. (2015). Cryogenic Engineering: Fifty Years of Progress. Springer.

ISO 21014 – Cryogenic Vessels – Temperature and Pressure Measurement Guidelines.