The Ingenious Application of Thread Connection on Flange

Flange connection is a kind of detachable fixed connection, which is widely used. Thread connection has the advantages of simple structure, reliable connection, convenient assembly and disassembly, etc.. 

The thread connection is usually used for the connection where nominal diameter under DN 50, and needs to disassemble the connection part of the pipe. Compared with the detachable flange connection, the structure and size of the thread connection is small. But the flange connection is more reliable, due to the precision of thread processing is difficult to guarantee the complete seal, in strength, it is relatively lower than the welding connection. Therefore, the pipe thread connection is usually used for conveying water, air and other fluid mediums, even if leakage happens, the perniciousness is relatively light, or used on lining pipeline where welding may lead to the coating peeling. It is advisable to avoid pipe thread connection in which the gap corrosion, severe erosion or cyclic load may happen.

The thread sealing pipe produced in China has two standards: GB / T12716 (thread of sealing pipe , 1/ 16 ~ 24°) and GB7306 (thread of sealing pipe  55, 1 / 16 ~ 6°).The standard thread taper of GB/T12716 is 1:16; the tooth angle is 0; the thread mark is NFI. The standard is equivalent to the use of ASME B1.20.1; the standard thread taper of GB7306 is 1:16; the tooth type angle is 55; the thread mark code is RC / R2 and RP / Rl. The standard is equivalent to the use of ISO7 - 1. The two kinds of taper pipe thread cannot be exchanged. 

The standard of thread flange in China GB14626 stipulates the type, size parameters of the forged steel threaded flange; the pressure rating, according to the nominal wall thickness of reference pipe, is divided into three strength grades: Seh80, Schl60 and XXS (DN8 ~ 100). ANSI B16. 11 stipulated 20001b, 30001b and 60001b. The size ranges from DN6 to 100, a total of 12 specifications. It should be noted that the pipe thread connection flange is only applicable to inch tube series.

The calculation of strength of flange bolt joint is mainly according to the connection structure, material properties and loading state to analysis the strength and failure forms of bolt, and then according to the corresponding calculation criterion to calculate minor diameter D1, then in accordance with the standard selected the nominal thread diameter D and the pitch P etc.. The rest size of Bolt and nuts, washers, etc., users can be on the nominal diameter D to select directly from the standard, because when formulating the standard, every part of nuts, bolts, and the strength and manufacturing and assembly requirements of washer have been considered into.