What exactly is the creep and relaxation phenomenon of gaskets? In this session, we will focus on creep and relaxation behavior and conduct an in-depth analysis of the relevant characteristics of gaskets.
In a sealing system composed of bolts, gaskets and flanges, the creep and relaxation of gaskets has a specific definition. It is neither simple material creep nor stress relaxation alone, but a resultant effect of the interaction between gaskets and bolts.
The gasket stress originates from the tensile force generated by bolt elongation, which is converted into compressive force acting on the gasket. When the gasket undergoes creep and its thickness decreases, the bolts will lose part of the compression constraint and shrink, leading to changes in bolt elongation. This further reduces the compressive force borne by the gasket, namely the gasket stress.
This cyclic process — gasket creep → change in bolt elongation → variation of gasket stress — is defined as the creep and relaxation of gaskets.
Manhole gasket for BMC voltage regulator
Flange joints with different sealing surfaces present distinct extreme conditions: joints with flat sealing surfaces tend to experience pure creep, where the bolt elongation is much greater than the gasket creep. By contrast, metal-to-metal groove surface joints or flat joints with high rigidity are prone to pure relaxation.
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