What is the tightening sequence of flanges and bolts?

The tightening sequence of flanges and bolts is essential to ensure the tightness and safety of the connection. Here are some common flange and bolt fastening sequences:

First, the general tightening sequence

Initial fastening:

Use a target torque value of about 30%(or 50%, depending on the actual situation) for initial tightening to ensure that the gasket is in the correct position and the initial connection is established.

Intermediate fastening:

Raise to a target moment value of 70%(or continue to use an increasing moment value, such as 80%) to further evenly load the preload force.

Final fastening:

Apply 100% target torque value to complete the tightening. This step usually needs to be repeated several times to ensure an even distribution of the preload.

Second, the cross method

The cross method is a common flange bolting sequence that is suitable for most flange connections.

Number and location:

The pre-tightening bolts on the flange can be numbered in a clockwise sequential numbering system or a symmetrical cross numbering system.

Make sure the gasket is positioned correctly, usually with 4 screws at positions 1, 2, 3, and 4 to ensure that the center of the wound gasket is within the edge of the flange.

Tightening sequence:

Tighten in the order of the cross. For example, if a symmetrical cross-numbering system is used, the tightening sequence can be performed according to the bolt number, such as 1-2-3-4; The 5-6-7-8. 9-10-11-12.

At each fastening, ensure that the clearance along the circumference of the flange is uniform, and check the fastening of the nut.

Repeat fastening:

If necessary, repeat the above tightening steps until the predetermined tightening torque value is reached.

Third, special tightening sequence

For flanged connections with a large number of bolts (such as 24 bolts), a more complex tightening sequence may be required to ensure an even distribution of preloading forces. For example:

Group fastening:

Divide the bolts into groups, with each group containing adjacent bolts.

Tighten each set of bolts in a certain order, such as clockwise or counterclockwise.

Increasing torque tightening:

In each group of bolts, tighten progressively according to the torque value from small to large.

After completing one set, turn to the next set for tightening.

Final full tightening:

After the initial and intermediate tightening of all bolts, the final full tightening is carried out to ensure that each bolt reaches the predetermined torque value.

Fourth, precautions

Avoid over-tightening:

Excessive tightening may cause bolts to break, flanges to deform, or gaskets to be damaged.

Tighten with the correct torque values and tools and follow the manufacturer’s guidelines.

Check and record:

During the fastening process, periodically check the fastening of bolts and the clearance of flanges.

Record the fastening data of each bolt (such as the type of wrench used, the value of torque applied, etc.) for future maintenance and reference.

Safe operation:

During the fastening process, ensure the safety of the working area and comply with the relevant safety procedures.

Use appropriate personal protective equipment, such as gloves and goggles.

To sum up, the fastening sequence of flanges and bolts needs to be determined according to the specific situation, and follow certain principles and methods to ensure the tightness and safety of the connection.