Analysis of Causes for Abnormally High Daily Evaporation Rate in Cryogenic Storage Tanks

An abnormally high daily evaporation rate (boil-off rate) in cryogenic storage tanks can lead to operational inefficiency, increased product loss, and potential safety hazards. Identifying the underlying causes is essential for timely corrective measures.

1. Insulation Degradation or Damage

Vacuum Loss in Insulation: In double-walled tanks, loss of vacuum in the insulation layer significantly increases heat ingress, accelerating evaporation.

Mechanical Damage: Cracks, gaps, or crushed insulation layers compromise thermal resistance, allowing more heat to reach the liquid.

Aging Materials: Over time, insulation effectiveness may decrease due to moisture ingress or material deterioration.

2. Tank Structural Issues

Leaks or Micro-Cracks: Small leaks in the tank shell or welded joints allow ambient heat and air intrusion, increasing vaporization.

Surface Corrosion: Corrosion or pitting reduces the thermal barrier, contributing to higher boil-off rates.

Improper Tank Geometry or Deformation: Warping or sagging may alter the tank’s thermal behavior and stress distribution, increasing heat transfer.

3. Operational Factors

Overfilling or Rapid Fill Cycles: Introducing large amounts of liquid too quickly can create turbulence, disturbing the liquid surface and promoting evaporation.

Excessive Venting: Frequent operation of pressure relief valves or venting systems can increase the measured boil-off rate.

Pressure Control Abnormalities: Low operating pressure reduces the liquid’s boiling point, leading to higher evaporation rates.

4. Environmental Influences

High Ambient Temperatures: Elevated surrounding temperatures or direct solar radiation increase heat transfer through the tank walls.

Wind and Convection Effects: Strong air currents around the tank can enhance convective heat transfer, leading to greater evaporation.

5. Instrumentation or Measurement Errors

Faulty Sensors: Inaccurate level, pressure, or temperature sensors may give the impression of higher boil-off than actual.

Calibration Issues: Incorrectly calibrated flow meters or level gauges can misrepresent evaporation rates.

Conclusion
Abnormal increases in daily evaporation rate in cryogenic storage tanks usually result from insulation failure, structural damage, operational mismanagement, environmental stressors, or measurement errors. Regular maintenance, proper tank operation, and accurate monitoring are critical to identifying and mitigating these causes, ensuring safe and efficient cryogenic liquid storage.

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.