5.6　Gaskets

5.6.1　Selection of gaskets shall be based on the nature of fluid，service temperature，pressure，and flange sealing surface.The load applied on the sealing surface of gaskets shall be commensurate with flange design pressure，design temperature，type of sealing surface，surface roughness，flange strength and fasteners.Selection of gaskets shall meet the requirements in current national standard GB/T 4622.3 Specification of Spiral Wound Gaskets.

5.6.2　The material of gaskets shall be selected according to the temperature range specified in the reference standards listed in this code，and shall not cause any detrimental effects when exposed to certain medium or temperature.

5.6.3　Selection of gaskets shall comply with the following requirements:

1　Flexible graphite spiral wound gaskets should be used as flange gaskets.For the piping with PN≤10 and design temperature below 150℃，nonmetallic gaskets are an alternative.For spiral wound gaskets，the material of the inner ring shall be selected according to the fluid conveyed and the design temperature of the medium and piping，and the material of the outer ring shall be selected according to the design temperature of the piping.

2　For RF flanges，gaskets with locating rings or a combination of inner ring and locating ring should be used，rather than general purpose gaskets or gaskets with only the inner ring.

3　For MF flanges，spiral wound gaskets with inner ring shall be used.For RF flanges，gaskets with outer locating ring should be used.

4　The outer diameter of nonmetallic gaskets may be larger than that of the sealing surface of RF flanges，called self-centering gaskets.

5.6.4　The content of chloridion in nonmetallic gaskets intended for stainless steel flanges shall not exceed 200 mg/L.