IMPORTANCE OF TORQUE MOMENTS AND SEQUENCES
When it's time to change the gasket, you want to do it as soon as possible, so that stopped processes can be started as soon as possible. Well, although the goal is to do it in the shortest possible time, it is necessary and extremely important to follow a few simple rules, so that there are no unnecessary complications that can arise due to improperly installed gasket. The procedure is simple: after removing the gasket, cleaning and checking the flange, screws and other parts for dirt, cracks, etc., and possibly replacing worn and/or damaged parts, the gasket is installed. Before installing the gasket, the screws should be lubricated, as well as the inner part of the nut that will come into contact with the flange. Graphite copper or molybdenum sulfate grease has proven to be the most effective in practice, with copper being ideal in high temperature environments. Next comes the positioning of the gasket. Regardless of the size of the gasket, it should be handled with care, so that it does not break or get damaged. At least two people are needed for larger size gaskets, it is not at all recommended to position large size gasket independently, as damage to the gasket is almost guaranteed.
RECORDS AND CALCULATION OF TORQUE MOMENTS
Once the gasket is in place, and the screws are in place, it's time to tighten. If the person who installed the previous gasket did their job responsibly, there will be records of the torque moments used on the flange in question. If so, your work will be done quickly. However, if there are no records, you will have to calculate the torque moments yourself, and write them down to have them ready for the next time you need to change the gasket.
You will get your target torque moments from a calculation that will rely on the data on the sealing surface, the pressure on the gasket and the load on the screws. The torque moments must be sufficient to compress the gasket so that it can perform the sealing, which largely depends on the sealing material. You or a competent engineer will know how to fix it.
Image source: eriks.co.uk
TIGHTENING PROCESS –GOLDEN RULE 30 – 60 – 100
Once the calculation is done, you need a calibrated torque wrench to tighten the screws. Be sure the key is properly calibrated and certified. Calibration does not happen once, but the key must be recalibrated approximately every 5,000 cycles or 12 months.
It is extremely important to tighten the screws in the correct sequence (pattern) and in stages, in order to prevent damage to the gasket. First, the screws are lightly tightened by hand, then each screw is tightened with a wrench to 30% of the full torque, after that the tightening starts again, following the same pattern, but this time each screw is tightened to 60% of the full torque, and after it is tightened again according to the same pattern, this time until it is fully tightened -AND ALWAYS DIAGONALLY!
Example of torque sequence depending on the number of screws
Image source: eriks.co.uk
Image source: eriks.co.uk