Today we will discuss the mechanical behavior performance of gaskets, focusing on creep relaxation behavior.
Understanding the law governing creep relaxation occurrence enables better prevention of sealing failure.
For most flange joints, creep relaxation mainly occurs within 15 to 20 minutes after bolt preloading, or within 20 to 25 load cycles. Beyond this stage, creep relaxation slows down gradually and finally stabilizes.
Based on this characteristic, the industry has a practical recommendation: retighten bolts 18 to 24 hours after initial bolt preloading to recover part of the bolt load. This practice is more applicable to high-temperature working conditions, as high temperature exerts a far greater impact on creep than room temperature—sometimes over ten times the creep magnitude observed at room temperature.
It should also be noted that the creep rate generally rises with the increase of initial gasket stress (with rare opposite cases).
In practical engineering applications, stress relaxation caused by gasket creep is also referred to as "torque loss". This is because the pre-tightening torque of bolts has a direct correlation with bolt elongation (i.e., gasket stress); a drop in torque indicates loss of gasket stress.
We will elaborate on practical cases regarding the specific applications of stress relaxation and creep relaxation in the next session. Stay tuned!
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