1. Inspection of flange fasteners

    ● Gaskets: During installation, ensure that the gaskets are new, clean, and dry, and check for any defects or damage to the gaskets; Old gaskets cannot be reused; Before installation, confirm that the size and grade of the gasket used are consistent with the identification of the flange.

    ● Flange: Before installation, check if the flange surface is damaged, such as scratches, nicks, mud, corrosion, and burrs. When the depth of dents and scratches that pass through the water line of the flange sealing surface in the radial direction exceeds 0.2mm, and the covering surface exceeds half of 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 if the flange is aligned according to the pipeline installation requirements in section 6.2 of SH3501-2011.

    ● 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 shall be free of dirt, rust, double skin, scratches, burrs, debris, and other external substances that affect torque during the tightening process; Welding or machining methods are not allowed to repair bolts; After the flange is installed and tightened, at least two threads are exposed outside the nut; Before using bolts and nuts, lubrication treatment must be carried out to ensure low friction coefficient during bolt tightening and improve the anti slip and corrosion performance of bolts and nuts; The screw threads, nut threads, and contact surfaces must be degreased and dried before using lubricating oil; Unified lubricating oil should be properly used for bolt threads, nut threads, nut bearing surfaces, washers, and nut support surfaces on flanges; Use high-temperature anti biting agent as needed.

2. Bolt tightening method

    ● Non torque ring wrench or hammer wrench: suitable for tightening general equipment and pipeline flanges, selected based on bolt size and flange pressure rating. The tightening requirements are as follows:

       1） The maintenance unit formulates a tightening plan, symmetrically tightening the flanges and numbering them in the tightening sequence, as shown in Figure 1 and Figure 2.

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

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

       4） According to the on-site equipment and flanges, the calculation is based on tightening one circle, and the number of tightening times (at least 3 times) and the impact load (force) for each tightening are reasonably determined. The impact load (force) for tightening should be tightened from small to large (such as 50%, 80%, and 100% increase), and the load should not be too fast or too large to prevent gasket sealing failure.

       5） The sequence of each tightening of a torque free ring wrench or hammer wrench: tighten the two radially opposite bolts to the predetermined hammer load (force) of the bolt; Tighten another pair of bolts approximately 90 degrees apart from the previous two bolts along the circumference; Continue tightening until all other bolts are tightened to the predetermined hammer load.

       6） Finally, tighten all bolts in a clockwise or counterclockwise direction at 100% hammer load (force).