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Causes of gasket failure
Nov 13, 2018

1, the sealing gasket pressure distribution is uneven

The unevenness of the pressing force is caused by many factors. The first is the human factor. The asymmetric pre-tightening bolt during construction is easy to cause unevenness. This factor can be eliminated during construction. Theoretically, when the flange is pressed, the sealing surface is Absolutely parallel, but in reality, the centerline of the pipe cannot be absolutely concentric, so the bending moment is generated on the flange when the bolt is tightened, so that the flange is not evenly stressed. This uneven connection causes the sealing surface to be deformed more or less, so that the sealing pressing force is reduced, and leakage is likely to occur under running load. Finally, the bolt arrangement density has a significant influence on the pressure distribution. The closer the bolt is, the more uniform the pressure is.

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2, gasket stress relaxation and torque loss

Stress relaxation and torque loss are also the main causes of leakage. After the bolt is tightened on the flange, due to the vibration of the machine, the increase or decrease of the temperature, etc., the stress relaxation phenomenon will occur in the gasket during the working process, and the bolt torque will also gradually decrease, resulting in torque loss and leakage. In general, bolts are long, the residual torque is large, and the smaller the diameter, the more advantageous it is to prevent torque loss. Therefore, the use of long and thin bolts is an effective way to prevent torque loss. In addition, the greater the temperature change, the longer the duration, and the more severe the torque loss. Heating the bolts for a certain period of time to stretch them and maintaining a given torque is effective in preventing torque loss. Also, the thinner the gasket, the smaller the torque loss. In addition, the machine and the pipeline itself are prevented from vibrating strongly, and the influence of vibration of the adjacent equipment is eliminated, and the sealing surface is not unnecessarily hit, and the bolts after fastening are not hit, so that the torque loss can be prevented.

3, the sealing surface did not meet the corresponding requirements

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, the roughness is Ra6.3~3.2, and the sealing surface precision of the soft gasket can be low. Some, the roughness Ra25~12.5 can be. However, the sealing surface must avoid radial mechanical nicks, burrs and other mechanical damage.

The flatness of the sealing surface and the perpendicularity of the sealing surface to the axis of the flange are prerequisites for ensuring uniform sealing of the gasket. The sealing surface is unclean, mechanical damage and corrosion damage, and residual old gaskets may also cause the gasket. The seal failed.

4, the gasket material does not match

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. Suitable gasket deformation as elastic force is a necessary condition for forming a seal, and the gasket deformation includes 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 fit well with the sealing surface, does not harden due to low temperature, and does not soften or plasticize due to high temperature. The natural sealing effect is good.

5, the temperature affects the choice of gasket

The decrease in temperature also has a large effect on the leakage. The leakage of the flange joint often occurs during cooling, because the cooling speed of the flange and the bolt is different when cooling, the stress relaxation caused by the pressing force of the sealing gasket after cooling, and the cold shrinkage of the pipe, the direction of the bolt stretching The force, this force will promote the leakage. When selecting the sealing gasket in the low temperature medium, attention should be paid to the elastic gasket at low temperature; the thickness of the gasket should be as small as possible, the flange gap should be as small as possible; Bolts make the stress smaller.