1. Temperature -- part of material volatilizes in high temperature gasket, resulting in gasket shrinkage and hardening.

2. Medium -- Medium can dissolve gasket or some components in gasket. Medium will reduce gasket strength.

3. Temperature fluctuation -- different expansion and shrinkage rates of metal and non-metal materials, resulting in the reduction of bolt pretightening force.

4. Pressure fluctuation -- pressure fluctuation causes gasket permanent deformation and yield.