The necessity of thermal tightening the small floating head after heat exchanger maintenance
Thread Content
After the maintenance of the heat exchangers in our factory, steam is generally used at around 110 degrees to carry out slight floating-head tightening on the tube side. However, some people question this practice, arguing that it is unnecessary and may even affect the resilience of the gasketing. I would like to hear everyone’s opinions on this.
1 Is the small floating head overheating after the heat exchanger maintenance? Perhaps we have different definitions of a small floating head – does it refer to a floating head? If it is a floating head, how should it be heat-tightened? Please share your experience. 2 I personally hold a negative view on heat-tightening. 3 The guarantee of sealing during normal use depends on factors such as the material of the bolts, the type and material of the gaskets, and proper installation to ensure even loading on the bolts. 4 Most leaks are caused by uneven initial loading on the bolts. The issue that still needs to be addressed in hot tightening is the uniform distribution of bolt loads, a problem that can be resolved simultaneously in the cold state
1. By \"hot tightening of the small floating head,\" I mean the process that takes place before the installation of the large floating head; in our factory, the installation of the large floating head is the final step in the maintenance of heat exchangers. 2. During maintenance, our factory does not replace all of the bolts on the small floating head, but it ensures that either all of the bolts on a given floating head are brand new or all of them are used ones, taking into account the issue of bolt stress relaxation； 3. Our factory’s heat exchangers use wound gaskets. When a tightening force is applied, an excessive force can affect the gasket’s resilience; therefore, it is not necessary to tighten them tightly in the cold state – some slack should be left for tightening during operation, so as to bring the conditions as close as possible to normal operating conditions and ensure even stress distribution on the bolts ； 4. Uneven initial load is only one of the reasons for leakage; I believe that fluctuations in the device cause temperature changes, while the reduced resilience of the gaskets is another important factor contributing to leakage.
When the operating temperature of the equipment falls within the following range, the bolts on the flanges must be tightened thermally; the specific requirements are as follows: 1. 350 degrees ≥ operating temperature of the equipment > 230 degrees – in such cases, the bolts on the flanges must be tightened thermally. The assembly drawing should indicate that during trial operation, the bolts should be tightened thermally after maintaining the operating temperature for 24 hours. During thermal tightening, for equipment with a design pressure of ≤6 Mpa, the pressure inside the equipment shall not exceed 0.3 Mpa; for equipment with a design pressure > 6 Mpa, the pressure inside the equipment shall not exceed 0.5 Mpa. 2. When the operating temperature of the equipment is >350 degrees, the bolts on the flange must be tightened thermally twice. The assembly drawing should indicate that during trial operation, after maintaining the operating temperature for 24 hours, the bolts should be tightened thermally twice. The first heat-setting temperature is 350 degrees, with a second heat-setting being carried out at the operating temperature. During thermal tightening, for equipment with a design pressure of ≤6 Mpa, the pressure inside the equipment shall not exceed 0.3 Mpa; for equipment with a design pressure > 6 Mpa, the pressure inside the equipment shall not exceed 0.5 Mpa.
In my opinion, thermal tightening is indeed very necessary. It is an important step in every maintenance and operation process. Although it differs from the thermal tightening used in floating-head heat exchangers, the goal achieved is the same. Whether thermal tightening is required depends on whether the temperature of the fluid flowing through the equipment or pipes is high; failing to carry out thermal tightening can very likely lead to leaks. The concept of thermal tightening was developed after experiencing many difficulties, such as the initial load on bolts and the rebound of gaskets. . . . It’s okay to discuss it theoretically, but don’t equate it with reality. Given the precision of bolt processing in China and the actual conditions at the installation site, the theoretical tightening torque often isn’t sufficient to ensure that no leaks occur.
This should be stated in the device’s user manual.
The small floating head of the heat exchanger in high-temperature areas must be thermally tightened! It is also very necessary to support the original poster – floating-head heat exchangers tend to loosen up during startup and shutdown processes. Over the years of operation, we have suffered losses due to leaks caused by loose small floating-head bolts. In summer, when saturated steam is used, the temperature can reach up to 130 degrees; in winter, it’s already quite difficult to get the temperature to 110 degrees during maintenance!
Many manufacturers tighten the small floating head bolts and then weld them in place, which is very practical
Hehe, I think it’s still really necessary to use heat compresses
Soldered shut??? It’s supposed to be used as a disposable heat exchanger, but that seems a bit inappropriate, doesn’t it?
Do the flange bolts on the pipeline also need to be tightened by heating?