When selecting the fasteners for flange connection, the operating pressure, operating temperature, medium type and gasket type should be taken into account.
Gasket’s type and operating pressure, operating temperature, are directly related to the strength of the fastener material requirements.
For example, Japanese standard flange low toxic medium pipeline Spiralwound gasket sealing connection, although the pipeline operating pressure and temperature is not high, but because of the spiral wound gasket to form initial seal than the pressure, which requires fastener loads is also large,
Therefore, in this case, it is necessary to use high strength alloy steel.
Alloy steel studs shall be made of high quality steel. The material should be added after the letter A, such as 35CrMoA, 25CrMoVA according to the structure of different bolt can be divided into six hexagon head bolts and studs (also called stud) two, and the stud is divided into two kinds of harness and harness.
Six angle head bolts: often with the national standard flange and non-metallic gasket for ease of operation conditions. Six corner bolts are commonly used materials BL3 or Q235B;
Stud bolt and flange with the use of American Standard: often harsh conditions in operation conditions, which, because of changes in shape without type stud on the harness, the bearing capacity is strong.
Instead of stud type harness is relatively weak capacity. The nut material is often determined according to the bolt material that fits with it.
Under normal circumstances, the nut material should be slightly lower than the bolt material, and to ensure that the nut hardness is lower than the hardness of about HB30.
Source: China Pipe Fittings Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)