What type of flange’s sealing surface has water marks?

Steel pipe flanges, gaskets, and fasteners – HG20592-1997, Table 6.0.1 on page 11: Types of sealing surfaces. Note: For raised-face flanges with PN≤4.0 MPa, non-metallic flat gaskets, PTFE-lined gaskets, and flexible graphite composite gaskets can be used; serrated water lines can be machined on them, and the sealing surface code is RF(A). Table 6.0.1 Sealing surface types, Page 291 of HG20615-1997. Note: For raised-face flanges with PN≤5.0 MPa, non-metallic flat gaskets, PTFE-lined gaskets, and flexible graphite composite gaskets can be used; tight-groove water lines can be machined on them, and the sealing surface code is RF(A). In other words, other types of sealing surfaces cannot have precision grooved water lines machined. Using rigid gaskets such as metal wound gaskets results in an even worse sealing effect for the tightly grooved water lines.

First, it is necessary to understand what a fine-patterned water line is Many people think that without a waterline, the smoother the sealing surface, the better – but that’s wrong! Metal wound gaskets also require a surface with an appropriate roughness; it’s not the case that the smoother, the better! !

It is only permitted when using a low-pressure convex flange seal with non-metallic gaskets; the use of metal gaskets or under high pressure is not allowed.