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Selection and Scope of Eight (8) Types of Flange Gaskets (IV)

04 Asbestos Resin Board and Impregnated Asbestos Board Gasket

It is mainly used for pipes, pumps, valves, inlet and outlet flanges of various acid media, with the service temperature of 80 ℃ and the pressure below 0.6MPa.

Asbestos woven gasket is applicable to low pressure and high temperature conditions with pressure below 0.1MPa and temperature not exceeding 800 ℃. According to the specific requirements of the equipment, gaskets with different width, thickness and diameter can be woven. Or cut the asbestos band and apply it directly on the flange surface. It is used at the interface of large sulfuric acid and nitric acid oxidation furnaces and some unprocessed equipment, and the effect is far better than the original asbestos rope.

05 Metal-clad Asbestos Gasket

The asbestos plate or asbestos rubber plate is covered by metal sheet, which makes it not contact with the medium directly, avoids the decline of the strength of asbestos fiber, overcomes the leakage phenomenon, and thus expands the scope of use of the asbestos rubber sheet.

Generally, the service temperature of metal-clad asbestos gasket is 450 ℃ (some can reach 600~700 ℃, such as in the flue gas with atmospheric pressure~0.16 MPa), and the service pressure is 4 MPa, up to 6 MPa. If the pressure increases again, the gasket is prone to cross flow, and the core material is extruded from the overlap.

Because the metal-clad asbestos gasket requires a large bolt tightening force, even when the service pressure is lower than 2.45MPa, the flange below pg25kg cannot be used. Otherwise, the rigidity of flange and bolt will be insufficient, resulting in deformation and sealing failure. Some people believe that if the core material is changed to synthetic rubber with good elasticity, its tightening force will decrease. In fact, it is not, because the fastening force is absorbed by the core material after the core material is softened, which cannot provide the fastening force required for the metal plate to fit on the flange surface, and the gasket is easily damaged. In addition, in the medium containing more chloride ions and acidic medium, crevice corrosion is easy to occur at the overlap of stainless steel and iron sheet packing gaskets.

If the temperature is higher than 450 ℃, ceramic fiber or carbon fiber can be used as the core material. Flexible graphite is the most suitable core material. At present, metal-clad flexible graphite gaskets have been produced in batches in China. Its application effect is better than that of metal-clad asbestos gasket.

The metal packing gasket can be made into various shapes, and is widely used in various heat exchangers, large covers of reactors, loading and unloading holes, manhole flanges, etc. Iron clad gasket with a diameter of 2m has been made in China and is in good use.

A layer of flexible graphite sheet is pasted on the surface of the metal-clad gasket. Compared with the same kind of metal-clad gasket that is not covered on the surface, this gasket has smaller preload and better sealing performance. 

Unfinished (to be continued) ……


Post time: Mar-14-2023