1. Technical requirements for fastening of equipment and pipeline flange installation process

(1) Inspection of flange fasteners

● Gasket: When installing, make sure that the gasket is new and clean and dry, and check whether the gasket is defective or damaged; the old gasket cannot be reused; before installation, confirm the size and grade of the gasket used and the flange identities are consistent.

● Flange: Before installation, check whether there is any damage on the flange surface, such as scratches, nicks, mud, corrosion and burrs, dents radially passing through the waterline of the flange sealing surface, and the depth of scratches exceeds 0.2mm, and When the coverage exceeds half the width of the gasket sealing surface, the flange must be replaced or the sealing surface must be reprocessed and repaired; the position of the nut support surface on the back of the flange should be parallel and smooth; check whether the flange is centered, and the inspection method should be in accordance with SH3501-2011 6.2 Pipeline installation requirements.

● Bolts and nuts: Check whether the bolts and nuts are used correctly according to the equipment and pipeline design requirements; the threads and contact surfaces must not have dirt, rust, heavy skin, nicks, burrs, debris and other foreign substances that affect the torque during the tightening process ;

It is not allowed to repair the bolts by welding or machining; after the flange is installed and fastened, at least two threads are exposed outside the nut; the bolts and nuts must be lubricated before use, so that the bolts have a low coefficient of friction when fastened And improve the anti-slip and anti-corrosion properties of bolts and nuts; stud threads, nut threads and contact surfaces must be degreased and dried before using lubricating oil;

The bolt thread, nut thread, nut bearing surface, gasket, nut bearing surface on the flange should be properly used with uniform lubricant; high-temperature anti-seize agent should be used as needed.

(2) Bolt fastening method

● No-torque ring wrench or hammer wrench: suitable for general equipment and pipeline flange fastening, selected according to bolt size and flange pressure level. Fastening requirements are as follows:

1) The maintenance unit formulates a fastening plan, fastens the flange symmetrically, and numbers the fastening sequence, refer to Figure 1 and Figure 2 for numbering.

2) Position the gasket with 4 bolts at positions 1, 2, 3, and 4 to ensure that the center of the wound gasket is within the edge of the flange.

3) Tighten the set bolts by hand, then insert the other stud bolts and hand-tighten to balance the load, making sure that at least 2 threads are exposed at each end of the nut.

4) According to the on-site equipment and flange, one fastening circle is regarded as one calculation, and the number of fastening times (at least 3 times) and the hammering load (strength) of each fastening are reasonably determined, and the tightening hammering load (strength) is Tighten in order from small to large (such as 50%, 80%, 100% increments), and the load should not be too fast or too large to prevent gasket seal failure.

5) The sequence of each tightening of the torque-free ring wrench or hammer wrench:

Tighten the two radially opposite bolts to the predetermined hammering load (strength) of the bolts;

Tighten another pair of bolts about 90 degrees apart from the previous two bolts along the circumference;

Continue tightening until all remaining bolts are tightened to the specified hammer load.

6) Finally, according to 100% hammering load (strength), tighten all the bolts clockwise or counterclockwise one by one.

figure 1

 

Figure II

 

● Torque wrench: suitable for high temperature and high pressure, flammable and explosive equipment and pipeline flanges. Fastening requirements are as follows:

1) The maintenance unit needs to formulate a fastening plan, formulate an appropriate torque, and conduct a design review based on parameters such as bolt strength, gasket initial sealing specific pressure, working sealing specific pressure, and medium pressure to prevent bolts from breaking and gaskets from being compressed. Excessive force and loss of elasticity lead to seal failure.

2) Fasten the flange symmetrically, and number the fastening sequence, refer to Figure 1 and Figure 2 for numbering.

3) Position the gasket with 4 bolts at positions 1, 2, 3, and 4 to ensure that the center of the wound gasket is within the edge of the flange.

4) Tighten the positioning bolts by hand, then insert the other stud bolts and hand-tighten to balance the load, making sure that at least 2 threads are exposed at each end of the nut.

5) According to the on-site equipment and flanges, one tightening circle is regarded as one calculation, and the number of tightening times (at least 3 times) and each tightening torque are reasonably determined, and the tightening torque is tightened in order from small to large (such as 50%, 80%, 100% increments), the load should not be too fast or too large to prevent gasket seal failure.

6) The sequence of each tightening of the torque wrench:

Tighten the two bolts that are diametrically opposed to the specified torque of the bolts;

Tighten another pair of bolts about 90 degrees apart from the previous two bolts along the circumference;

Continue tightening until all remaining bolts are tightened to the specified torque.

7) Finally, tighten all the bolts clockwise or counterclockwise according to the 100% torque value.

8) Record the torque value for reference in future maintenance.

● Bolt tensioner: suitable for high temperature and high pressure, flammable and explosive equipment and pipeline flanges. Fastening requirements are as follows:

1) The maintenance unit formulates a fastening plan, formulates an appropriate tensile force, and conducts a design review based on parameters such as bolt strength, gasket initial sealing specific pressure, working sealing specific pressure, and medium pressure to prevent bolts from breaking and gaskets due to pressure. Excessive tightening force and loss of elasticity lead to seal failure.

2) When the bolt tensioner stretches and tightens the bolts individually (step by step), according to the principle of bolt tightening uniformity, refer to the tightening sequence of the torque wrench for tension and tightening.

3) During the tensioning and tightening process of the bolt tensioner, the number of times of tensioning and tightening should be reasonably determined, and the pressure should be increased in order from small to large (such as 50%, 80%, 100%), and the pressure should be uniform. Every time a certain pressure is increased, It should be increased after the pressure is stabilized to avoid excessive impact tension and affect the pre-tightening effect of the bolts.

4) Record the pressurized value for reference in future maintenance.

 

2. Thermal tightness requirements for equipment and pipeline temperature rise during construction

(1) Carry out thermal fastening according to the temperature in Table 1

Table 1 Hot and cold fastening temperature of equipment and pipeline Unit: ℃

Note: For those whose working temperature is between -29 and 250°C, heat tightening and cold tightening are not required.

(2) Hot fastening or cold fastening should be carried out after the temperature of equipment and pipelines is stable. Explosion-proof tools should be used. During the fastening period, no operations such as heating up or boosting pressure can be performed.

(3) When tightening, it is recommended to start from the point where the gap between the flanges is the largest and tighten symmetrically. If there is a leak, perform a tight leak first.

(4) During the heating process of equipment and pipelines during the start-up period, fastening quality checks are required. Use a torque wrench to check 100% torque value or use an explosion-proof hammering tool to hammer the nuts in the tightening direction to check whether they are loose.