Tips for checking the tightness of flange bolts

Make a mark once it’s tightened properly. Of course, don’t apply sufficient torque all at once; tighten it symmetrically as well.

When tightening the bolts, they are usually tightened diagonally, not all of them at once, to leave some play for final adjustment

Personally, I think it’s important to develop a *habit when tightening bolts – for example, always turning a bolt by a certain angle each time. Once it’s cooked, you’ll know that bolt wasn’t tightened properly.

Whether pre-tightening is done using a hydraulic torque wrench or a tensioner, if the number of tools used differs from the number of bolts, the application of hydraulic force must be done in stages; in other words, the pre-tightening torque or tension force must be applied gradually. While grading, the lock nuts must also be properly numbered; only through such grading and numbering can the bolts be tightened correctly. However, when there are a large number of bolts, what is the quick way to verify if one of them is not tightened to the required pressure level? Here are some tips: Due to interference effects, if a bolt isn’t tightened properly, tapping its head gently with a small hammer will produce a sound different from that of the other bolts – bolts that are properly tightened will make a “Ring, ring, ring” sound, while those that aren’t tightened properly will emit a “Ding, ding, Dong” sound. This is great for experimenting! This post was last edited by Laojiu on 2009-4-4 16:50]

Use a torque wrench to check each bolt with the appropriate torque (determined by the minimum preload); if the bolt can still be tightened, it means it wasn’t tightened properly – tighten it symmetrically until it can no longer be turned； It is also important to ensure that the flange spacing is even; otherwise, there may be foreign objects on the contact surface or a bolt might be tightened too much at once ； The bolts should not be tightened too much, as this can damage the gaskets or cause the bolts to break, leading to accidents.

We* usually number them first according to the principle of cross symmetry, and then tighten them in order. Important equipment should be tightened 2 to 3 times.

Symmetrical tightening is required, and it needs to be done several times – usually three times

First, pre-tighten everything; in terms of symmetry, there are usually no problems

First, tighten the bolts symmetrically, and while tightening the bolts check whether the flange surfaces are parallel to avoid misalignment. Then, following the principle of symmetric sorting, tighten them one by one to develop a systematic and orderly habit: use 50% of the force in the first round, 90% in the second round, and 100% in the third round; after three rounds, it will be done.