Issues regarding thermal tightening and airtightness when starting up and shutting down short-cycle equipment
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Two sets of equipment, at a temperature of 300°C and a pressure of 13 MPa. The medium is a mixture of alcohols, and it is necessary to switch it every month. The equipment that has been taken out of service needs to have its fluid replaced; during this process, the equipment that is offline must have its temperature and pressure reduced, while the other equipment’s temperature and pressure must be increased. I would like to ask whether heat tightening and airtightness testing are required each time a switch is made every month. If so, what is an appropriate temperature for heat tightening? Is it 150°C or 300°C? Or is it not necessary to conduct airtightness and heat tightening tests since the interval between switches is one month? It would be helpful to have relevant information on this topic. Thank you
Appendix: For two sets of periodic switching, are the related devices required to be airtight and thermally sealed?
I just found a standard, but it only specifies the heat-shrinking temperature; it also emphasizes that the internal pressure during heat-shrinking must not exceed 0.5 MPa. However, heat-shrinking is usually carried out when the reaction starts up. Does that mean it’s necessary to raise the temperature first and then the pressure? Should the pressure be kept below 0.5 MPa until the temperature reaches the operating level, and only then be increased after heat-shrinking? Additionally, based solely on this standard, it seems that heat-shrinking would need to be performed each time. I’m seeking help from experts in this area
Personally, I think heat sealing is necessary; the working temperature is sufficient for heat sealing, and airtightness is also required. Areas that have been opened should be inspected carefully.
But how should the pressure for heat tightening be chosen? Should it be done at the operating pressure, or at a pressure below 0.5 MPa?
Thermal tightening is carried out after 2 hours at the operating temperature; pressure is increased after thermal tightening, and thermal tightening under pressure poses significant safety risks. If your bolts have not been removed and reinstalled, it is not necessary to conduct a leak test; the fact that there is no leakage at room temperature does not guarantee that there will be no leakage when the temperature rises. For pipelines with temperatures exceeding 200 degrees, it is necessary to perform thermal tightening each time they are switched.
So, heat tightening must be done every time, while the airtightness test is only necessary for bolts that have been moved, is that right? In other words, during the first start-up, heat tightening and airtightness testing are carried out separately: first, the temperature is raised to carry out heat tightening, and then pressure is applied to test airtightness
There is no need to conduct a leak test if the components have not been disassembled. The leak test must also be carried out before feeding begins. The gas used for this test should be dry, clean air, nitrogen, or some other inert gas. The test pressure should correspond to the design pressure, and the test is generally conducted at room temperature; conducting it at 300 degrees does not comply with safety standards. If you have removed the pipelines, conduct a gas-tightness test on each pipeline separately; if the equipment is not used, simply tighten it after heating it up.
Okay, thank you very much for your answer
To replace the catalyst, it’s necessary to remove the flanges; the areas that are removed need to be tightened again as the temperature rises, and it’s not a problem to tighten the other areas as well
But if we go by this approach, one of our processes requires the pressure to be increased to over 10 MPa. If we first raise the temperature for heat tightening and then increase the pressure, at a rate of 1 MPa per hour, plus the time needed for heat tightening, that would result in an additional 10 or so hours of operating time each time. Since these two reaction systems need to be switched every 1500 hours, it’s indeed a waste of time