Regarding the issue of preheating thickness
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Dear experts, I have a question: As shown in the diagram, it is a joint type where the pipe is inserted into cylinder D, and the weld does not penetrate completely; the weld depth is 8 mm while the cylinder thickness is 80 mm. Is preheating required for such a joint before welding? What we usually refer to as preheating of thick plates – different preheating requirements are specified depending on the thickness, and does this thickness refer to the thickness of the base material or the thickness of the weld?
Thicker materials require preheating, as without it their cooling rate will be fast, which can affect the structural changes that occur.
So, whether to preheat or not is determined based on the thickness of the base material or the thickness of the weld? For example, in a thick plate structure like the one shown above where full penetration welding is not achieved, the base material is very thick while the weld itself is only a few millimeters thick – is preheating necessary?
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Whether preheating is required and the preheating temperature should be determined based on the material and the thickness of the weld joint. It is not specified in this diagram what material it is, so it’s difficult to determine. As for the preheating thickness, it is determined based on the thickness of the welded joint; 8 mm will suffice. This structure is the same as the connection weld of the heat exchanger tube sheet.
Joint thickness. . The definition of joint thickness can be found in GB150.4, under the section on post-weld heat treatment. .
Hello, regarding the issue of preheating thickness, it is based on the thickness of the joint, right, and has nothing to do with the thickness of the base material? Taking 47105 as an example, the Fe-1 material joints require preheating only when they are 25 mm thick; for the fillet welds at the tube ends of heat exchange tubes made of 16MnD material, although the tube sheets are thick, the thickness of these welds is usually only a few millimeters. In such cases, isn’t it unnecessary to preheat these welds?
I don’t think it’s necessary; the thickness of the welded joint is not great. If full-thickness penetration welding is to be used, not only preheating is required, but stress-relief heat treatment as well.