Leakage Risk Analysis of Low-Temperature Liquid Storage Tanks

Low-temperature liquid storage tanks, such as those used for LNG, LPG, and liquid nitrogen, operate under extreme cryogenic conditions. Leakage from these tanks poses significant safety, environmental, and economic risks. A comprehensive leakage risk analysis is essential for designing preventive measures and ensuring safe operation.

1. Potential Leakage Sources

Material and Structural Defects:
Cryogenic steels and nickel alloys can experience microcracks, welding defects, or material embrittlement at low temperatures, which may lead to leakage under pressure. Improperly fabricated welds or flawed heat treatments exacerbate this risk.

Seals and Nozzles:
Flanged connections, gaskets, valves, and nozzles are potential weak points. Differential thermal contraction between tank components can compromise sealing effectiveness.

Corrosion and Erosion:
Internal corrosion from impurities in stored liquids or external corrosion due to environmental factors may lead to wall thinning and eventual leakage. Erosion at high-velocity inlets/outlets can also create local thinning.

Operational Factors:
Overfilling, pressure surges, thermal cycling, and sudden temperature fluctuations can induce stress beyond design limits, causing cracks or seal failure.

Mechanical Damage:
Accidental impacts during transportation, maintenance, or installation can compromise structural integrity, leading to potential leakage.

2. Risk Assessment Methods

Failure Mode and Effects Analysis (FMEA):
Identifies possible failure points, evaluates their severity, occurrence, and detectability, and prioritizes risk mitigation strategies.

Finite Element Analysis (FEA):
Simulates thermal stresses, pressure loads, and mechanical impacts to predict potential crack initiation or deformation points.

Leak Detection Systems:
Continuous monitoring with pressure sensors, liquid level gauges, and gas detectors helps identify early signs of leakage. Automated alarm systems allow rapid response.

Probabilistic Risk Assessment (PRA):
Evaluates the likelihood and consequences of tank failure scenarios, integrating statistical data on material properties, operational conditions, and historical incidents.

3. Preventive Measures

Material Selection: Use cryogenic-compatible steels (e.g., 9% Ni, austenitic stainless steel) with verified low-temperature toughness.

Welding Quality Control: Apply strict welding procedures, non-destructive testing, and post-weld heat treatment to eliminate defects.

Proper Design: Incorporate thermal expansion allowances, overpressure protection, and redundant sealing systems.

Maintenance and Inspection: Regular ultrasonic testing, radiography, and visual inspection of tank walls, welds, and fittings.

Emergency Response Planning: Implement containment systems, safety valves, and emergency shutdown protocols to mitigate consequences of leakage.

Conclusion
Leakage in low-temperature liquid storage tanks can result from material, structural, operational, or environmental factors. Systematic risk assessment, proper material selection, high-quality fabrication, and continuous monitoring are essential to minimize leakage risks and ensure safe long-term operation.

References

EN 14620 – Design and Manufacture of Cryogenic Vessels.

API 620 – Design and Construction of Large, Welded, Low-Pressure Storage Tanks.

ASME Boiler and Pressure Vessel Code, Section VIII – Rules for Construction of Pressure Vessels.

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

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