Petrochemical Industry – Fastening Operation Steps of Flange Bolts
(Last Updated On: May 31, 2023)
In the petrochemical industry, the most common bolt fastening is the flange bolt of the pipeline. In this article, TorcStark will introduce in detail the tightening of flange bolts of petrochemical pipelines and the operation steps of using different bolt tools to tighten flange bolts.
1. Fastener inspection of petrochemical pipelines and equipment:
1.1 Gasket inspection:
1.1.1 Confirm that the size and pressure rating of the gasket is consistent with the mark on the flange. 1.1.2 Make sure the gasket is new, clean, and dry. 1.1.3 Confirm that the gasket is free from any defects and damages. 1.1.4 Old gaskets cannot be reused. 1.1.5 Check whether the gasket has quality problems.
1.2 Inspection of flanges:
1.2.1 Check the flange surface and contact surfaces for damage such as scratches, nicks, mud, corrosion, burrs, etc. 1.2.2 Check whether the material, specification, and pressure level of the flange is consistent with the pressure of the piping equipment designed and installed on site. 1.2.3 Check whether the position of the nut crimping surface on the flange surface is parallel and smooth. 1.2.4 Check the flange for quality problems.
1.3 Inspection of bolts and nuts:
1.3.1 Check whether the specifications, models, and materials of bolts and nuts are consistent with the design. 1.3.2 There shall be no dirt, rust, nicks, burrs, slips, debris, or other internal and external factors affecting the torque during the tightening process on the thread contact surface. 1.3.3 After the flange is installed and tightened, at least two threads are exposed outside the nut. 1.3.4 Bolts and nuts must be lubricated before use so that the bolts have a low friction coefficient and improve the anti-slip and corrosion resistance of bolts and nuts. 1.3.5 Stud threads, nut threads, and contact surfaces must be degreased and dry before using lubricating oil. 1.3.6 The bolt threads, nut threads, nut bearing surfaces, washers, and nut support surfaces on flanges should be properly used with uniform lubricating oil, and high-temperature anti-seize agents should be used as needed.
1.4 Check the flat washer and spring washer:
1.4.1 Check whether the materials, specifications, and pressure ratings of flat gaskets and spring gaskets are consistent with the designed and installed pipelines. 1.4.2 Check whether the washers and spring washers are matched with the bolts and nuts. 1.4.3 Check the appearance of the gasket for dirt, unevenness, and defects.
Suitable for important equipment and pipeline flanges such as high temperature and high pressure, flammable and explosive. It needs to be selected according to the bolt size, flange pressure level, or working conditions.
2.2.1 Make a fastening plan and make an appropriate torque. According to the bolt strength, the initial sealing specific pressure of the gasket, the working sealing specific pressure, the medium pressure, and other parameters, the design review is carried out to prevent the bolt from breaking and the gasket from losing elasticity due to excessive compression force, resulting in sealing failure. 2.2.2 For flanges to be fastened symmetrically, the fastening sequence should be numbered first. 2.2.3 Position the gasket with bolts at a symmetrical position to ensure that the center of the wound gasket is within the edge of the flange. 2.2.4 Tighten the positioning bolts by hand, then insert other stud bolts and hand-tighten them to balance the load, making sure that at least 2 threads are exposed at each end of the nut. 2.2.5 According to the on-site equipment and flange, it is calculated as one tightening circle. Reasonably formulate the number of tightening times (at least 3 times) and the impact load (strength) of each tightening. Tighten the impact load (strength) in order from small to large, and do not load too fast or too large to prevent gasket seal failure. 2.2.6 The sequence of each tightening of the torque wrench: Tighten the two radially opposite bolts to the specified torque of the bolts. Then tighten another pair of bolts about 90 degrees apart from the previous two bolts along the circumference. Finally, continue to tighten until all other bolts are tightened to the specified torque. 2.2.7 Finally, tighten all the bolts clockwise or counterclockwise according to the 100% torque value. 2.2.8 Record the torque value for future reference.
It is suitable for important equipment and pipeline flanges such as high temperature and high pressure, flammable and explosive, and the fastening requirements are as follows:
2.2.1 Formulate a fastening plan and formulate an appropriate tensile force. According to the bolt strength, the initial sealing specific pressure of the gasket, the working sealing specific pressure, the medium pressure, and other parameters, the design review is carried out to prevent the bolt from breaking and the gasket from losing elasticity due to excessive compression force, resulting in sealing failure. 2.2.2 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 tensioning and tightening. 2.2.3 During the tensioning and tightening process of the bolt tensioner, the number of times of tensioning and tightening should be reasonably determined, the pressure should be applied in order from small to large, and the pressure should be uniformly applied. Every time a certain pressure is increased, the pressure should be stabilized and then increased. In order to avoid excessive impact tension, affecting the pre-tightening effect of the bolt. 2.2.4 Record the pressure value for reference in subsequent recording work.
2.3 Heat-tightening and cold-tightening steps for heating up equipment and pipelines:
2.3.1 Hot fastening or cold fastening should be carried out after the temperature of equipment and pipelines is stable. Explosion-proof tools are used, and operations such as heating up and boosting pressure are not allowed during fastening. 2.3.2 When fastening, start from the place with the largest flange gap and fasten symmetrically. If there is a leak, tighten it first. 2.3.3 During the heating process of equipment and pipelines, fastening quality inspection is required. Use a torque wrench at 100% torque value or use an explosion-proof hammering tool to hammer the nuts in the tightening direction to check whether they are loose.
3. In the end
The bolt fastening of pipelines and equipment in the petrochemical industry is the most important link in preventing leakage, reducing losses, protecting the environment, and protecting the safety of life and property. TorcStark recommends using high-standard bolting tools while following standard flange and equipment bolting procedures. Hydraulic wrench, bolt tensioner, electric torque wrench, etc. will be the best choice. Welcome to contact TorcStark professional engineers and get bolt solutions for free.
Preventing leakage and protecting the environment starts with tightening the bolts!