5.7　Fasteners

5.7.1　Fasteners shall include hexagon bolt，studs with equal-length threads on both ends，nuts，and washers.The selection of fasteners shall comply with the provisions in relevant current national standards such as GB/T 9125 Fasteners for Pipe Flange Joints.

5.7.2　Selection of flange fasteners shall comply with the following requirements:

1　The fasteners shall offer satisfactory gasket sealing under the pretightening and operating parameters.

2　The fasteners for high temperature application shall have a thermal expansion coefficient basically equal to that of flanges.

3　In cases where PN≤25 and operating temperature t≤250℃，for connecting the flanges with nonmetallic gaskets，hexagon bolts specified in the current national standard GB/T 901 Double End Studs-Product Grade B or GB/T 5785 Hexagon Head Bolts with Fine Pitch Thread may be used，and the type I hexagon nuts specified in the current national standard GB/T 6170 Hexagon Nuts，Style I or GB/T 6171 Hexagon Nuts，Style I，with Fine Pitch Thread may be used.

4　In cases where PN≤40 and operating temperature t≤250℃，for connecting flanges，double-end studs specified in the current national standard GB/T 901 Double End Studs-Product Grade B or GB/T 5785 Hexagon Head Bolts with Fine Pitch Thread should be used，and the type I hexagon nuts specified in current national standard GB/T 6170 Hexagon Nuts，Style I or GB/T 6171 Hexagon Nuts，Style I，with Fine Pitch Thread should be used.

5　In addition to the above paragraphs（3）and（4），in cases where PN≤100 and operating temperature t≤500℃，dedicated double-end studs specified in the current national standard GB/T 9125 Fasteners for Pipe Flange Joints shall be used，and the hexagon nuts specified in the same standard shall be used.

6　The hardness of matching nuts shall be lower than that of the bolts.