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Why Does PE Gasket Fail?

Update:07 May 2022

Reasons for PE Gasket Failure:

1. The uneven pressing force is caused by many factors. The first is the human factor. Asymmetrical preloading of bolts during construction can easily cause unevenness. This factor can be eliminated during construction. In theory, when the flange is pressed, the sealing surfaces are absolutely parallel. However, in practice, the centerline of the pipeline is impossible. Absolutely concentric, so when the bolt is tightened, a bending moment is generated on the flange, which makes the flange stress uneven and uniform. This asymmetrical connection makes the sealing surface more or less deformed, which reduces the sealing pressure, and it is easy to leak under the operating load. Finally, the bolt arrangement density has a significant effect on the pressure distribution. The closer the bolts are, the more uniform the pressure will be.

2. Stress relaxation and torque loss are also the main causes of leakage. After the bolt is tightened on the flange, due to the influence of mechanical vibration, temperature increase or decrease, and other factors, the gasket will undergo stress relaxation during the working process, and the bolt torque will gradually decrease, resulting in torque loss and leakage. Generally speaking, the longer the bolt, the larger the residual torque, and the smaller the diameter, the better It is more beneficial to prevent torque loss. Therefore, using long and thin bolts is an effective way to prevent torque loss. In addition, the larger the temperature change and the longer the duration, the more severe the torque loss. It is effective to prevent torque loss by heating the bolt for a certain period of time to elongate it, and then maintaining a given torque. Also, the thinner the gasket, the smaller the torque loss. In addition to preventing the machine The strong vibration of the pipeline itself, the elimination of the influence of the vibration of the adjacent equipment, the unnecessary impact on the sealing surface, and the knocking of the tightened bolts, etc., can prevent torque loss.

3. The shape and roughness of the flange sealing surface are matched with the gasket. Generally, the sealing surface in contact with the metal gasket requires high dimensional accuracy, and the roughness is Ra6.3~3.2, while the sealing surface accuracy of the soft gasket is required. It can be lower, and the roughness is Ra25~12.5. However, the sealing surfaces must be free from radial mechanical nicks, burrs, and other mechanical damage. The flatness of the sealing surface and the sealing surface and the flange shaft The verticality of the line is the premise to ensure that the gasket is evenly pressed, and the sealing surface is not clean, there are mechanical damage and corrosion damage, and the remaining old gasket will also lead to the failure of the gasket seal.

4. The gasket material is the main factor affecting the performance of the gasket. The gasket material should be dense and not easy to impregnate the medium. Appropriate gasket deformation, like elastic force, is a necessary condition for forming a seal, and gasket deformation include elastic deformation and plastic deformation. At the same time, it can withstand temperature, pressure fluctuation, and medium corrosion. If the gasket material has good elasticity and softness, it can kiss the sealing surface well. It is not hardened due to low temperature, nor softened or plasticized due to high temperature, and the natural sealing effect is good.

5. The decrease in temperature also has a greater impact on leakage. The leakage of flange connection often occurs during cooling, because the cooling speed of the flange and the bolt is different during cooling, the stress relaxation of the compression force of the gasket after cooling, and the cold shrinkage of the pipeline, produce the tensile direction of the bolt. The force of this force will cause leakage. When choosing a gasket in the low-temperature medium, should be Pay attention to the use of elastic gaskets at low temperature; the thickness of the gasket should be as small as possible, and the flange gap should be as small as possible; high-strength bolts should be used to reduce the stress.