What is the range of octagonal pads and oval pads?

The octagonal pad and elliptical pad for the trapezoidal groove face flange (commonly known as "soil ring" in the refining industry) have good sealing performance. On the tapered surface of the groove, the octagonal pad is in face contact and the elliptical pad is in line contact. Therefore, the elliptical pad has good adhesion under low fastening force, but needs to be tightened twice; and the octagonal pad is generally not easily leaked after being fastened once. Their shortcomings are that they require a large bolt tightening force. When used for low pressure and high temperature conditions, the flange rating must be above pg25 kg.