Why is thermal tightening required for heat exchangers during startup?

Materials expand when heated and contract when cooled; if thermal tightening is not carried out, leakage will occur at the flange surfaces of the heat exchanger once hot materials enter it. Not only cooling exchange equipment, but all equipment with an operating temperature above room temperature must be heat-tightened.

It’s the principle of thermal expansion and contraction; otherwise, the seal at the inlet will leak. If you don’t believe it, give it a try

⑴When the unit is put into operation, the main body of the heat exchanger equipment and its accessories are connected using flanges and bolts, with gaskets used for sealing. Due to the difference in materials between these components, during heating, especially when the temperature exceeds 200°C, uneven expansion occurs, resulting in relaxation of the flange surfaces and a decrease in the sealing pressure. At high temperatures, the elastic modulus of the materials decreases, leading to deformation and a reduction in mechanical strength. This causes localized excessive stress on the flange, prompting plastic deformation; as a result, the elastic force is lost. At this point, pressure has a significant impact on the sealing material, either causing the gasket to move along the flange surface and leading to leakage. The purpose of thermal tightening is to eliminate any relaxation in the flange, so that there is sufficient pressure on the sealing surfaces to ensure effective static sealing.

During the heating process, the flange and bolts are not heated evenly, and they expand at different rates; as a result, the bolts expand more than the flange, which means the bolts effectively become longer. If they are not tightened properly, this can lead to leaks.

Because after being heated, the difference in expansion coefficients between the connectors and the main body of the equipment leads to loosening, which in turn causes leaks; failing to tighten them properly will exacerbate the leakage problem and result in fires or explosions

2# 498400160 From what I remember, heat tightening is required only when the temperature is above 250°C, right?

Since different materials have different coefficients of expansion, their lengths change at various temperatures. At normal temperatures, the bolts on the flange are tight; however, as the temperature rises, the bolts may loosen due to the differences in the expansion coefficients of the materials. Therefore, it is necessary to retighten them after the temperature increases. This is necessary to ensure the sealing performance of the flange.

It is necessary to apply heat tensioning in order to prevent the bolts of the flange from expanding as temperature rises; otherwise, the bolts may loosen, resulting in a reduced seal between the flange and the gasket and an increased risk of leakage. This approach ensures the flange’s sealing performance.

After the equipment is manufactured, it undergoes a hydrostatic test to ensure it meets the required standards; the entire process takes place at room temperature. When the device is put into operation, thermal expansion of the equipment may cause leaks in the seals, so thermal tightening is necessary