Where to use fasteners for pipes

The pipe flange standards used for important pipe connections at home and abroad are mainly two systems, namely the European system (in DIN

Standards as a representative) and the American system (ASME B16.5 and B16.47 standards in the United States as a representative). The pipe flange standards of countries in the same system are basically compatible with each other (connection size and sealing surface size). Two different systems cannot be used with each other.

(1) The relevant regulations of GB50316

1. Fasteners for pipelines: including hexagon head bolts, stud bolts, hexagon nuts and washers, etc.

2. Choose standard fasteners in the current national standards, and select materials in the specified special purpose

3. The fastener materials used for flange connection should comply with the current national flange standards and be compatible with flange gaskets.

4. The thread pitch of the fasteners for flange connection should not be greater than 3mm, and the fasteners with a diameter of M30 or more can use fine thread.

5. Carbon steel fasteners should meet the operating temperature specified in the current national standards

6. Under severe cyclic stress conditions, the bolts or stud bolts used for flange connection shall be made of alloy steel.

(2) Relevant regulations of 'General Rules for Equipment'

1. Flange fasteners should be able to ensure that the gasket reaches the initial sealing condition and maintain the gasket's tightness during the entire operation.

2. Hexagon head bolts are suitable for PN≤2.0MPa or full-thread bolts or equal-length stud bolts under high temperature conditions.

3. The yield strength does not exceed 235MPa. Low-strength fasteners are only suitable for flange connection of non-metallic gaskets with PN≤2.0MPa, and should not be used in severe cycling situations. Carbon steel low-strength fasteners are within the operating temperature range. It is -20℃～200℃.

4. When deformation-hardened austenitic stainless steel fasteners are used for non-soft gasket flange connections, the load-bearing capacity of the fasteners should be checked to see if they can meet the connection requirements, and the service temperature should not exceed 500°C.

5. Should comply with 'Fasteners for Pipe Flanges' (SH3404) or relevant standards.

(3) Selection of bolts and nuts for flange connection

Bolts are divided into single-head bolts and double-head bolts according to their appearance. Single-head bolts are threaded only on one end of the screw, and the other end is the screw head connected to the screw body. Single head bolts for flanges usually use hexagon head bolts. Both ends of the stud bolt are threaded, and the shape is cylindrical. When the tightening force is large, the single-head bolt is easy to break at the joint between the screw and the screw head, so it cannot be used on medium and high pressure flanges. Stud bolts can not only be used on medium and high pressure flanges, but also facilitate tightening from both sides.

Nuts for flanges are generally hexagonal, divided into two types: single chamfer and double chamfer. The surface of the single-chamfered hex nut in contact with the connected part is flat, and only the other side is chamfered; both sides of the double-chamfered hex nut are chamfered. Therefore, the contact area with the connecting piece is that the contact surface of the single-chamfered hex nut is large, and the contact surface of the double-chamfered hex nut is small.

Bolts are divided into crude bolts, semi-refined bolts and refined bolts according to the manufacturing method. Except for the threaded part, the outer surface of the rough bolt is not finished, it is the rough shape of the blank. The bolts are mostly made of plain carbon steel, and the tension force it bears is not high. Semi-refined and refined bolts need to be processed, and some need to be heat treated. They are mostly used in the manufacture of high-quality carbon steel or alloy steel, so they have large tensioning force and high temperature resistance.