2. Check for dents, scratches, rust residues, and oil on the surface of the equipment. The surface roughness of the flange surface should not exceed 6.3um. If the surface roughness does not meet the requirements, repair the flange surface, inspect the flange, bolt holes, etc., and clean the flange surface.

3. The flange protrusion should be leveled and smooth, without hand spikes or axial pipe grooves; The threaded part of the threaded flange should be detailed and undamaged; The convex and concave sealing form of the convex surface should naturally fit together, and the height of the convex shape should not be lower than the depth of the dry concave groove.

4. Inspect and clean the bolts and nuts, and apply insulation layer vegetable oil to the threads of each bolt and nut.

5. Align the flanges at both ends to maintain the same pivot and parallel surface, and be careful when installing the gasket. Do not apply lubricant, vegetable grease, or adhesive to the gasket and flange surface to prevent damage to the sealing ring inside the gasket.

6. Align the bolt holes at both ends and use three broken nails spaced 120 degrees apart to thread them into the fixed fixed flange (especially for large and medium-sized flanges). At least two broken nails should be spaced 180 degrees apart.

7. Insert bolts, nuts, and sealing rings. The nuts that have been wiped with engine oil should be installed first with the stainless steel plate sealing ring. Pre tighten the bolts until the flange and gasket touch each other.

8. Use vernier calipers, hand cylinder tools, etc. to check the gap between the flange and gasket. If there is a gap, it indicates that the flange installation is not parallel.

9. If there is a gap, gradually loosen the nut and tighten it again until the two flanges and gasket touch each other. This method is also necessary to avoid misalignment caused by flange gasket contact; If the method is not reasonable, it can also cause the sealing ring of the gasket to be damaged due to excessive bolt load when the flange contacts the gasket.

10. According to Zhao's recommended bolt pre tightening torque (10-15% bolt torque), tighten the loose nut, remove the broken nail, replace the bolt, nut, and sealing ring, and pre tighten with the same torque.

11. During the bolt tightening process again, increase the pre tightening force to 50% of the bolt torque; Tighten the bolts again until the final torque is reached.

12. This is a safety operating procedure for reasonable pre tightening control of bolts, especially for software in large-diameter pipeline systems.

13. All actual operations above should use torque wrenches (mechanical equipment or hydraulic) or use bolt pre tensioners.