Why Do Flange Gaskets Fail?
First Type: Uneven Compression Force Causes Leakage:
1. Human Factors: Uneven tightening of bolts during construction can lead to an imbalance in compression force. This factor can be eliminated during construction.
2. Flange Misalignment: Flange misalignment affects the tightening force. Ideally, flanges should be perfectly parallel to the sealing surface. However, due to the pipe's centerline not being absolutely concentric, tightening bolts imparts moments to the flange, causing uneven and asymmetric loading. This deformation of the sealing surface results in reduced clamping force and is prone to leakage under working loads. The solution is to understand the deformation patterns of flanges, ensure uniform compression forces, and use gaskets to eliminate gaps, thus preventing leaks.
3. Bolt Spacing: The spacing of bolts also significantly affects pressure distribution. Smaller bolt spacing leads to more even pressure distribution.
Second Type: Stress Relaxation and Torque Loss:
Stress relaxation and torque loss are significant causes of leakage. After bolts are tightened on the flange, stress relaxation occurs during the working process of the gasket due to factors such as mechanical vibrations, temperature fluctuations, and changes in tension. This leads to a gradual reduction in bolt torque, resulting in torque loss and leaks. In general, longer bolts retain more residual torque, while smaller diameters are more effective at preventing torque loss. Using longer, thinner bolts is an effective method to prevent torque loss. Additionally, larger temperature fluctuations and longer durations lead to greater torque loss. Heating the bolts for a period, elongating them, and then maintaining a given torque can effectively prevent torque loss. Thinner gaskets result in smaller torque loss. It's also crucial to prevent strong vibrations of machinery and the piping system itself, as well as eliminate the influence of neighboring equipment vibrations, as this doesn't have a significant impact on the sealing surface, and torque loss can be prevented without rethreading the bolts.
Third Type: Surface Roughness Matching Sealing Surface Shape:
For successful sealing, the surface roughness of the flange should match the shape of the sealing surface. For example, under the surface form of a raised face (RF) sealing surface, higher surface roughness can affect the sealing effectiveness. Successful sealing requires controlling the degree of flange surface defects and avoiding significant surface imperfections such as deep scratches, grooves, or marks, as well as other surface flaws. Greater pressure is required to seal them.
Fourth Type: Temperature Changes and Cooling Affect Sealing:
Temperature changes and cooling have a significant impact on sealing. When pipes are installed at room temperature, they expand when heated and contract when cooled. Flange joints often experience leaks during the cooling process due to the faster cooling of the flanges and bolts compared to the cooling rate of the gasket. The cooling affects the gasket's compression force, stress relaxation, and the cooling shrinkage of the pipeline, resulting in tension in the direction of the bolt and causing leakage. Therefore, when selecting gaskets for low-temperature media:
1. Use low-temperature elastomeric sealing gaskets.
2. Make flange gaskets as thin as possible and minimize the gap between flanges.
3. Use high-strength bolts to reduce strain.
These measures will help to avoid leakage during temperature changes in low-temperature media.
The provided translation is an optimized summary of the content.
