How to perform post-weld heat treatment on jacketed vessels?
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I would like to ask the teachers: how should post-weld heat treatment be carried out for vessels with jackets? How should technical requirements be written?
We need you to specify the operating conditions so we can make a judgment!
It depends on your company’s production processes and so on.
First, weld the heat treatment backing plate to the inner container. After heat treatment, a hydrostatic test is conducted; once the hydrostatic test is successful, the jacket is welded.
The first method is overall heat treatment of the equipment: after the inner cylinder passes the inspection, a pressure test is conducted; once it passes, the jacket is welded, followed by a pressure test on the jacket. Overall heat treatment is then carried out, with separate pressure tests conducted on both the inner cylinder and the jacket. The second method, as mentioned on the 4th floor, involves using shims: after the inner cylinder passes the inspection, it undergoes overall heat treatment, followed by a pressure test. The jacket is then welded onto the inner cylinder, and that jacket is also subjected to a pressure test.
The first method has one risk: deformation of the outer jacket during heat treatment. Generally, the material used for the outer jacket does not require heat treatment
The first method violates the regulations. Any hydrostatic test must be carried out after heat treatment.
The voltage withstand test conducted earlier can serve merely as a means of process control for leak detection; it is the voltage withstand test performed after heat treatment that serves as the final inspection.
With stress, problems are likely to occur during hydrotesting.
We previously built a device of this type: after welding the inner cylinder, an air pressure leak test was conducted at 1.1 times the design pressure; thereafter, the jacket was welded, and then overall heat treatment was carried out. After the heat treatment, a hydraulic test was performed
If full heat treatment is required, the inner vessel and the jacket can be heat-treated separately, after which the joint weld between the inner vessel and the jacket can be subjected to local heat treatment.