During the trial run, is hot tightening performed?
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In previous projects, during commissioning, the project manager ordered hot tightening of the connections between pipes and equipment. Was this done correctly? Under what conditions are hot-state tightening and cold-state tightening performed? What issues should be noted?
It should be in a cold state, that is, tightened at room temperature. Tighten in the cold state, then expand – no stress loss. Tightening in the hot state results in stress loss after cooling. Thermal deformation is likely to occur at high temperatures; after tightening, certain deformation takes place due to the differences in the thermal expansion coefficients of metals (the cylinder head may warp to some extent). The amount of warping is calculated, and together with the multi-layer metal composite gasket currently in use, leaks are prevented. General assembly is carried out at room temperature, with a tightening machine being used to tighten all bolts simultaneously. During maintenance, there are requirements regarding the sequence of disassembly and assembly, as well as torque and angle adjustments.
Generally, before starting up high-temperature equipment and raising its temperature to a certain level, it is necessary to thermally tighten the connected flanges or manholes. Since gaskets are required for such connections, thermally tightening is needed once a sufficient temperature is reached to ensure a secure connection.