Leakage Cases Happen to Seal Gaskets of Flanges
For sealing materials, they suffer from contact pressure of bonding surface and elastic restoring force which is used to fastening external force. These forces lead to blocking effect. Therefore, seal gaskets come into play.
Leakage phenomena of general seal gaskets are classified into four types: leakage of interface, leakage of infiltration , leakage of diffusion and leakage caused by destruction.
1. Leakage of interface.
Leakage might happen when the gasket is not compressed enough or the surface finish of flange is not suitable. Of course, application of deformational flanges also lead to leakage. For this kind of leakage, stuffing space between a gasket and a flange with soft packing can successfully guard against the accident.
2. Leakage of infiltration.
Most of soft materials are made from fiber. Thus they are apt to be etched by media, especially under the function of pressure. Due to capillarity phenomena, media will infiltrate to the side with lower pressure and result in leakage.
3. Leakage of diffusion.
Concentration difference push media to leak though substance transfers taking place in sealing clearance or capillarity of sealing materials. Diffusion is the result of molecular movement. It is not one-way. Vacuum state and small pressure difference in sealing are liable to cause leakage of diffusion. What’s more, when the sealed substances are extremely toxic and radioactive, special attention should be paid in case of infiltration and diffusion. Permeable substances like nitrogen and hydrogen also require special notice.
4. Leakage caused by destruction.
This kind of leakage is caused by many facets, including terrible work environment, unsuitable installation, frequently shock, deformation, etc. Influence of it is the most serious among all leakage.
Different packings are used to match up various flanges. Flanges
with smooth surface are generally used together with soft and thin seal gaskets under low pressure. When exposing to high pressure, smooth flanges with enough intensity can also be applied into operation. In this case, however, we should select thick packings or seal gaskets with reinforcing rings. It should be noticed that metallic packings are not applicable in this circumstance. That is because pressing force needed here is excessively big and might cause serious deformation of bolts. Flanges on this occasion are difficult to by sealed tightly. If you have to use metallic packings, you should diminish smooth surface of flanges to make the small contact surface shrinks at the same. Therefore, with same tension of bolts, compressive stress of flange surface increases.