Reason: Pretension is too small.
1. Thermal expansion and cooling: In the same mechanical equipment, the bolts, gaskets, flanges, and fillers are all different in materials. At the same temperature change range, the thermal expansion and cooling speeds are different, so that under the temperature difference, the original precompaction will be Each will decrease, By overlapping with each other, the degree of relaxation of this pre-tightening force will be geometrically magnified, resulting in leakage;
2. Pressure fluctuation: the principle is the same;
3. Mechanical vibration: the principle is the same;
4. Chemical corrosion: principle above;
5. Fill letter volume: principle above.
Reason: Too much preloading.
Due to calculation errors or incomplete, the use of a disc spring with excessive pre-tightening force, if its pressure is too large and exceeds the yield limit of the gasket and bolt material itself, it also leads to leakage. In this case, the disc spring must be used to compensate, and its compensation is greater than the pre-tightening force required for the minimum seal, which is less than 75 % of the material yield limit.
In real work, there are usually two kinds of mistakes:
1. Select the pressure is too small: According to the physical characteristics of the bolt pre-tightening force, if the pre-tightening force relaxes 30 %, the minimum required for sealing cannot be reached, which is equal to the failure to install the disc spring;
2. Selection pressure is too large: if the disc spring elastic yield limit is exceeded or the stem is held dead, resulting in permanent deformation of the disc spring stroke exceeding 75 % of the inner cone height, it is equal to the artificial magnification bolt pre-tightening relaxation force, which is more harmful.