The issue of stress-relief heat treatment thickness
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Clause 4.6.2.5 of NB/T47015: . . . . . The maximum δpwht among the pressure vessel components that have not undergone post-weld heat treatment shall be used as the calculated thickness for post-weld heat treatment. a) Overall post-weld heat treatment of pressure vessels ； b) Multiple pressure vessels or components are placed in the same furnace. Question: b) Installing multiple pressure vessels or components in the same furnace – this is easy to understand; it means taking the maximum thickness among several (multiple) devices (or components) ； So, what does a) overall post-weld heat treatment of pressure vessels mean? Please ask a professional expert to answer!
After the pressure vessel is manufactured, it is placed in the furnace as a whole, or in sections, for heat treatment in accordance with the requirements for heat treatment
Thank you for your reply! But what I would like to ask is: Article 4.6.2.5 in NB/T47015:. . . . . The maximum δpwht among the pressure vessel components that have not undergone post-weld heat treatment shall be used as the calculated thickness for post-weld heat treatment. a) Overall post-weld heat treatment of pressure vessels ； b) Multiple pressure vessels or components are placed in the same furnace. Question: b) Installing multiple pressure vessels or components in the same furnace – this is easy to understand; it means taking the maximum thickness among several (multiple) devices (or components) ； So, what does a) overall post-weld heat treatment of pressure vessels mean?
In integral pressure vessels, different calculation pressures may be selected; as a result, the wall thickness of the vessel material varies depending on the calculation method used. For example, in towers, since the static pressures and loads acting on different parts vary, different design pressures are chosen, which leads to varying thicknesses in different sections of the tower. If heat treatment is applied to the entire vessel, then the maximum value of δpwht should be used as the key parameter to define the heat treatment process
Hello, thank you for your reply! Isn’t post-weld heat treatment meant to eliminate welding stress? ! Regarding the example of the tower you mentioned, I believe the maximum butt joint thickness can be used as the calculation thickness for heat treatment. But how should we choose this example below? For example: a liquid chlorine storage tank with a shell thickness of 18 mm and material 16MnDR; the manway stubs are made from 16MnDIII forgings with a thickness of 36 mm. This equipment requires overall heat treatment. The thickness of the manway stub when welded to the cylinder is much smaller than the thickness of the manway stub itself. Should 36 mm be used as the thickness for heat treatment calculations of this equipment during its overall heat treatment?
To be precise, the thickness for heat treatment is determined based on the thickness of the molten metal in the weld, that is δpwht, and not on the thickness of the material itself. For example, in the case of T-joints with wall thicknesses of 20 or 40, if stress-relief heat treatment is applied, then the thickness considered for heat treatment should be the thickness of the fillet weld. The same principle applies to butt joints; however, the heat treatment time needs to be selected carefully, taking into account the thickness of the base material, so as to ensure that the base material can be evenly heated within that time frame and secondary stresses can be eliminated
Well, thanks for getting back to me! Learned something new!