Why do you want to heat the pressure vessel after heat treatment?
The effect of heat treatment is to improve or recover the performance of the material, while eliminating the welding stress. The water pressure test after heat treatment is safe. At the same time, the pressure test is strength test, the experiment pressure more than design, after completion of test, the material will be residual compressive stress, for under internal pressure container, can improve its working state of stress. If the heat treatment is done after the test pressure, the benefit will be eliminated.
Some thick wall vessel, weld and influence area only after heat treatment can achieve the design performance, if not after heat treatment for pressure testing, may be broken because of the pressure is not enough.
Pressure vessel manufacturing process generally can be divided into: raw material acceptance process, line process, the cutting process, cleaning process, machining (including edge planing, etc.) work procedure, groups, and rolled to work procedure (product welding test plate), welding, NDT process, opening line process, the general inspection procedure and heat treatment process, pressure test process and corrosion process.
Because of the welding defects in the welded seam without the non-destructive flaw, the stress concentration will be formed around these defects. Without heat treatment after welding, welding parts also have larger welding residual stress. Both during the hydraulic pressure container, and hydrostatic stress superposition, easy to cause the container damage, therefore, should be the nondestructive flaw detection, ensure no excess in the weld defects, or after the heat treatment after welding, after eliminating welding residual stress, and then to water pressure test.
