A…Compressive stress must be appropriate to the gasket type. See the comments below for too little or too much compression.
Under-compression: Under-loaded gaskets will have higher leak rates and lower blowout resistance than properly loaded gaskets. This has a profound effect on performance and is the most frequent cause of joint problems.
Over-compression: Over-compression can lead to crushing, which accelerates the degradation of the gasket and can even cause immediate failure.
Uneven Compression: Gaskets resist blowout based on the friction of the gasket against the flange. The higher the compressive load, both initially and during service, the higher the blowout resistance. When areas of high and low compression exist in a flange joint, the areas of low compression are prime candidates for blowout.