Heat exchanger thermal tightening
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There are many heat exchangers at the construction site that require thermal tightening before they can be put into use. Is there any standard for thermal tightening of heat exchangers? What temperature should be used for this process, how many times should it be done, and what are the requirements during thermal tightening?
For the heat exchanger of our unit, the first thermal tightening is carried out at 100°C; thermal tightening is performed once for every increase of 100°C, with one final tightening done once the operating temperature is reached.
When I was involved in the installation and commissioning of power plants in the past, I would tighten the bolts once during the initial setup, and then tighten them again once the system reached normal operating pressure and temperature. By \"thermal tightening,\" what is meant is heating the bolts while tightening them; as the bolts cool down, their length decreases – this is based on the principle of thermal expansion and contraction.
Isn’t it contradictory to not allow bolts to be tightened or loosened under pressure, when this is exactly what hot tightening involves? Could some expert please explain this?
When tightening the bolts that connect the pipes, the maximum internal pressure of the pipes must comply with the following requirements: 1 When the design pressure is less than 6 MPa, the maximum internal pressure during hot tightening shall be less than 0.3 MPa; 2 When the design pressure is greater than 6 MPa, the maximum internal pressure during hot tightening shall be less than 0.5 MPa