The surface roughness of the flange sealing surface is one of the important factors affecting the sealing performance. It has been tested that when the surface roughness of the flange sealing surface is about Ra3.2μm, the air with a metal asbestos pad is used to seal the air with a pressure of 0.49 MPa, and the micro-leakage phenomenon is found; when the surface roughness is reduced to 1.6 μm, the sealing is good.
Various flange standards all has requirement for the surface roughness of the sealing surface, but because of the wide variety of gaskets, the roughness requirements are different, and the standards cannot be specified one by one. When using metal flat pad, metal toothed pad, metal wave pad and metal pad, the surface roughness of the flange sealing surface needs to be Ra 3.2 to 1.6 μm, which is difficult for the processing of the large diameter flange surface. The flexible graphite sheet on the surface can compensate for the disadvantages caused by the large surface roughness.