Finite Element (FEA) Thermal Shock analysis of a Cryogenic Ball valve.
Why FEA is required to validate the design:
Top entry type, high pressure cryogenic ball valves are subjected to variety of safety standards to prevent the type of accidents that can be caused by earthquake, leakage, explosion or fire.
Valve manufacturers need to validate the real scenario of such instances before installation of the equipment.
For this purpose, in this case study, Finite element analysis is carried to investigate the effect of structural safety and thermal stresses by thermal shock in a high pressure and a very low temperature conditions.Â
Key takeaways from FE Analysis –
To evaluate the structural safety of the valve components under high pressures and very low temperature conditions.
To understand the distribution of thermal stresses and deformation due to thermal shock in a cryogenic ball valve.
To assess the safety and reliability of ball valves used for the purpose of LNG handling and transportation.
To provide the basis for design and manufacturing of Cryogenic ball valves which are safe under the conditions of extreme temperature variances.
Test Specifications: Size - 16 inches Type - Floating Trunnion Ball valve Class - ASTM 351 Cryogenic class Material type - Alloy (Corrugated soft steel and graphite)
Test Conditions: Internal Pressure - 1.90 kgf/mm2 Cryogen temperature - (-195ËšC) Atmospheric temperature - 25ËšC Atmospheric pressure - 1 atm
FEA approach and Model setup:
The whole model is meshed with tetrahedron SOLID 45 elements and the mesh is checked for quality to remove any largely skewed elements.
The internal pressure due to the cryogen is specified on the trim and the temperature is also specified.
Transient (time-stepping) thermal analysis were conducted to evaluate the structure’s response to sudden temperature variance.
The material composition of different valve components (body, bonnet, ball, seats, thrust bearing etc.) were specified and contact were specified to simulate the real-case scenario.
Investigation of results:
Due to thermal swings, the valve components expands at different rates due different material properties or the duration of the components exposed directly to the cryogen.
Thermal stress distribution in the trim were evaluated due to the coupled effect of temperature and high pressure of the cryogen.
Deformation of different valve components caused due to thermal shock and high pressure were extracted.
From the results it is evident that the maximum stress appears at the center of the ball.
Conclusion:
In conclusion, Finite Element Analysis (FEA) is an essential tool for validating the design of Cryogenic Ball valves, which are critical components for handling and transporting liquefied natural gas. FEA helps to evaluate the structural safety of the valve under extreme conditions of high pressure and very low temperature, and to understand the distribution of thermal stresses and deformation caused by thermal shock.
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