How to tighten flange bolts scientifically?

Fastening technical requirements for installation process of equipment and pipeline flange

(1) Inspection of flange fasteners

Gasket:

During installation, make sure that the gasket is new, clean and dry, and check whether the gasket is defective and damaged; the old gasket cannot be reused; before installation, confirm that the size and grade of the gasket used are consistent with the flange identification.


Flange:

Before installation, check whether the flange surface is damaged, such as scratches, nicks, mud, corrosion and burrs. If the depth of the dents and scratches that run radially through the water lines of the flange sealing surface exceeds 0.2mm, and the coverage exceeds half the width of the gasket sealing surface, the flange must be replaced or the sealing surface must be reworked for repair. The position of the support surface of the nut at the back of the flange shall be parallel and smooth. Check whether the flange is right The inspection method is in accordance with the requirements of 6.2 pipeline installation in sh3501-2011.

Bolts and nuts:

Check whether the bolt and nut are used correctly according to the design requirements of equipment and pipeline; the thread and contact surface shall be free of dirt, rust, double skin, score, burr, debris and other external substances that affect the torque in the tightening process; it is not allowed to repair the bolt by welding or machining;
After the flange is installed and tightened, at least two threads are exposed outside the nut;
Before use, bolts and nuts must be lubricated to ensure low friction coefficient during bolt fastening and improve the anti sliding and anti-corrosion performance of bolts and nuts; stud threads, nut threads and contact surfaces must be degreased and dried before application of lubricating oil; unified nut support surfaces on bolt threads, stud threads, nut bearing surfaces, washers and flanges shall be properly used Lubricating oil; use high temperature anti seizing agent as required.

(2) Bolt fastening method

Torque free ring spanner or hammer spanner: applicable to fastening of general equipment and pipeline flange, selected according to bolt size and flange pressure grade. The fastening requirements are as follows:
1). The maintenance unit shall formulate the fastening plan, fasten the flange symmetrically, and number the tightening sequence. Refer to figure 1 and Figure 2 for numbering.
2)Position the gasket with 4 bolts at the positions of 1, 2, 3 and 4 to ensure that the center of spiral wound gasket is within the flange edge.
3)Tighten the set bolt by hand, then insert other stud bolts and tighten them by hand to balance the load, ensuring that at least two threads are exposed at each end of the nut.
4). According to the field equipment and flange, the tightening times (at least 3 times) and the hammering load (force) for each tightening shall be reasonably determined according to the calculation of one circle of tightening. The tightening hammering load (force) shall be tightened from small to large in order (such as 50%, 80%, 100% increase). The load shall not be loaded too fast or too large to prevent gasket sealing failure.
5)Tightening sequence of ring spanner or hammer spanner without torque:

  • Tighten the two bolts diametrically opposite to each other to the given hammering load (force) of the bolt;
  • Fasten another pair of bolts about 90 degrees away from the previous two bolts along the circumference;
  • Continue tightening until all remaining bolts are tightened to the established peening load.

6). Finally, tighten all bolts clockwise or anticlockwise according to 100% hammering load (force).
20200103063909 65711 - How to tighten flange bolts scientifically?

Figure.1

20200103061151 99975 - How to tighten flange bolts scientifically?

Figure.2

Torque wrench: suitable for high temperature, high pressure, flammable and explosive and other important equipment and pipeline flange. The fastening requirements are as follows:
1). The maintenance unit shall formulate the fastening scheme and appropriate torque, and carry out design review according to the bolt strength, initial sealing pressure of gasket, working sealing pressure, medium pressure and other parameters, so as to prevent bolt fracture and gasket failure due to the loss of elasticity due to too much pressing force.
2). Tighten the flange symmetrically and number the tightening sequence. Refer to figure 1 and Figure 2 for numbering.
3). Position the gasket with 4 bolts at the positions of 1, 2, 3 and 4 to ensure that the center of spiral wound gasket is within the flange edge.
4). Tighten the set bolt by hand, then insert other stud bolts and tighten them by hand to balance the load, ensuring that at least two threads are exposed at each end of the nut.
5). According to the field equipment and flange, the tightening times (at least 3 times) and each tightening torque shall be reasonably determined according to the calculation of one circle of tightening. The tightening torque shall be tightened from small to large in sequence (such as 50%, 80%, 100% increase). The overload shall not be too fast or too large to prevent gasket sealing failure.
6). Sequence of each tightening of torque wrench:

  • Tighten the two bolts diametrically opposite to each other to the set torque of the bolts;
  • Fasten another pair of bolts about 90 degrees away from the previous two bolts along the circumference;
  • Continue tightening until all remaining bolts are tightened to the specified torque.

7). Finally, tighten all bolts clockwise or anticlockwise according to 100% torque value.
8). Record the torque value for future maintenance.
Bolt stretcher: suitable for high temperature, high pressure, flammable and explosive and other important equipment and pipeline flange. The fastening requirements are as follows:
1). The maintenance unit shall formulate the fastening plan and appropriate stretching force, and carry out design review according to the bolt strength, initial sealing pressure of gasket, working sealing pressure, medium pressure and other parameters, so as to prevent bolt fracture and gasket failure due to the loss of elasticity due to excessive pressing force.
2). When single (step-by-step) tightening bolts are tensioned by bolt stretcher, according to the principle of bolt tightening uniformity, refer to the tightening sequence of torque wrench.
3). In the process of tension and fastening of bolt stretcher, the number of times of tension and fastening shall be reasonably determined, and the pressure shall be applied successively from small to large (for example, 50%, 80%, 100%). The pressure shall be uniformly applied. When a certain pressure is increased, it shall be increased after the pressure is stabilized, so as to avoid excessive impact tension and affect the pre tightening effect of bolt.
4). Record the pressurization value for future maintenance.

Hot tight requirements for temperature rise of equipment and pipeline during commencement

(1). Hot fastening according to table 1

Table 1 tightening temperature of equipment and pipeline in hot and cold state unit: ℃

working temperature Once hot and cold temperature Two hot and cold temperature
250~350 working temperature
>350 Three hundred and fifty working temperature
-70~-29 working temperature
<-70 -70 working temperature

Note: if the working temperature is between – 29 ~ 250 ℃, hot tightening and cold tightening are not required.
(2). Hot fastening or cold fastening shall be carried out after the temperature of equipment and pipeline is stable, and explosion-proof tools shall be used. During fastening, temperature rise, pressure rise and other operations cannot be carried out.
(3). When tightening, it is recommended to start from the place with the largest flange clearance and tighten symmetrically. If there is leakage, tighten it first.

(4). During the temperature rise process of equipment and pipeline during the start-up period, the fastening quality inspection shall be carried out, and the nuts shall be hammered with a torque wrench at 100% of the torque value or with an explosion-proof hammer to check whether they are loose according to the fastening direction.

Source: China Flange Manufacturer – Yaang Pipe Industry (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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how to tighten flange bolts scientifically - How to tighten flange bolts scientifically?
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How to tighten flange bolts scientifically?
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Check whether the bolt and nut are used correctly according to the design requirements of equipment and pipeline; at least two threads are exposed outside the nut after the flange is installed and tightened
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