- Measure the ID of the flange contact face.
- Measure the gasket ID.
- If the gasket ID is not at least 1/8 inch larger than the flange ID, do not use it unless it can be installed perfectly centered. In no instance should the gasket ID be less than 1/8 inch larger than the flange contact face ID when used between pipe or pressure vessel flanges.
A spiral-wound gasket does not have the same feel as other metallic, or even non-metallic, gaskets during bolt up. A spiral-wound gasket is different—more like a thick rubber gasket—because it “gives” as each bolt is tightened.
For this reason, it is important to tighten the bolts in small steps and in proper sequence.
Do not tighten the bolts all the way on the first attempt. This can tilt flanges out of parallel. If using a torque wrench, set the wrench at about one-third of the final torque for the first attempt.
Pay particular attention to the hard-to-reach bolts. Repeat the procedure with the torque wrench set at two-thirds of the final torque.
If the initial attempts at bolting up are done correctly in the proper sequence, the final attempt does not need to follow any set pattern.
What is important is that the final tightening be uniform, with each bolt evenly loaded. This is the best practice to achieve a trouble-free joint.
If the loads of each bolts are not uniform, the joint may leak, particularly if it is used in hot service.
Next Month: Back to Basics: Expansion Joints
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