Reliability Study of Pressure Vessel Sealing Structures under Extreme Conditions

Pressure vessels operating under extreme conditions—such as high pressure, high temperature, cryogenic environments, or corrosive media—require sealing structures that maintain integrity to prevent leaks, ensure safety, and preserve operational performance. Understanding the reliability of these sealing systems is critical for designing durable and fail-safe pressure vessels.

1. Factors Affecting Sealing Reliability

Thermal Stress and Expansion:
Extreme temperatures induce expansion or contraction of vessel walls and sealing components. Differential thermal expansion between flanges, gaskets, and vessel shells can compromise sealing integrity.

Mechanical Loading:
High internal pressure and external forces, including vibration, seismic activity, or operational loads, can deform sealing surfaces and reduce contact pressure.

Material Compatibility:
Sealing materials must withstand chemical attack, oxidation, and embrittlement in extreme environments. Metals, elastomers, or composite materials are selected based on operating conditions.

Creep and Relaxation:
At high temperatures, materials may experience time-dependent deformation, reducing sealing force over prolonged service periods. This is particularly significant for metal gaskets and elastomeric seals.

Corrosion and Wear:
Corrosive media or particulate-laden fluids can erode sealing surfaces, induce pitting, and accelerate leakage. Protective coatings and corrosion-resistant alloys improve longevity.

2. Reliability Assessment Methods

Finite Element Analysis (FEA):
Simulates contact pressure, stress distribution, and deformation of sealing surfaces under combined thermal and mechanical loads, identifying potential leak paths.

Failure Mode and Effects Analysis (FMEA):
Evaluates potential seal failure modes, their causes, consequences, and likelihood, guiding design improvements and preventive measures.

Experimental Testing:
Hydrostatic and pneumatic tests, thermal cycling, and accelerated aging experiments validate sealing performance under simulated extreme conditions.

Probabilistic Risk Assessment:
Integrates material variability, manufacturing tolerances, and operational uncertainties to estimate the probability of seal failure over the vessel’s service life.

3. Design and Preventive Measures

Gasket Selection: Use materials suitable for temperature, pressure, and chemical environment; metal-jacketed or spiral wound gaskets are common for high-pressure, high-temperature applications.

Surface Finish Optimization: Machined and polished sealing faces improve contact uniformity and reduce leakage risk.

Preload and Torque Control: Proper flange bolting ensures adequate initial compression of gaskets and compensates for relaxation over time.

Redundant Sealing: Secondary seals or double gasket systems enhance reliability in critical applications.

Conclusion
The reliability of pressure vessel sealing structures under extreme conditions depends on careful material selection, design optimization, and thorough analysis of thermal, mechanical, and chemical influences. Integrating computational simulations with experimental validation ensures robust sealing performance, reducing leakage risk and improving operational safety.

References

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

API 650 – Welded Tanks for Oil Storage.

Totten, G.E. (2006). Steel Heat Treatment: Metallurgy and Technologies. CRC Press.

Belytschko, T., Liu, W.K., & Moran, B. (2013). Nonlinear Finite Elements for Continua and Structures, 2nd Edition. Wiley.

Kou, S. (2003). Welding Metallurgy, 2nd Edition. Wiley.