Heat treatment issues of air preheaters
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For the welding of the tube bundles in the intermediate air preheater, the orifice plates at both ends are made of 12Cr1MoVR steel plates with a thickness of 25 mm, while the 6 partition plates in the middle are also made of 12Cr1MoVR steel plates with a thickness of 16 mm. All of these components need to be joined together, and heat treatment is necessary after welding. The orifice plate is welded to the tube; the tube is made of 12Cr1MoVG material with dimensions of D40*2.5 mm, and the weld root thickness is 3 mm. Is heat treatment necessary after welding? According to the GB/T 16507.5 standard for the manufacture of water-tube boilers, clause 9.3.5.4 specifies that for Fe-4-2 class materials, the circumferential butt welds of pressure components being ≤6 mm in thickness allow exemption from heat treatment. Alternatively, a non-compressed member can be connected to a compressed member; for fillet welds with a weld thickness of ≤13 mm, or for grooved welds as well as combined fillet and grooved welds with a weld thickness of ≤13 mm, preheating to above 150°C can exempt them from heat treatment. Can it be understood here that both the orifice plate and the partition are non-compressive components? Although there are seams between them, heat treatment can be omitted. The orifice plate is welded to the pipe, and the pipe, being a compressive component, is welded to these non-compressive components; with a weld leg thickness of 3 mm, can heat treatment be avoided by preheating?
Heat treatment serves one purpose: to eliminate internal stresses, and another: to prevent delayed cracking; it depends on the function of the workpiece
Process responsibility engineer determined in conjunction with design, welding, and heat treatment engineers!
A qualitative threshold is needed: when used as a pressure-bearing component, heat treatment is required if the thickness is over 6 mm. But what about components that are not pressure-bearing? Are there any relevant standard requirements in that case? It is well understood that heat treatment is used to remove hydrogen and relieve stress, but these goals can be achieved through preheating and post-heating holding. Not all manufacturers have heat treatment furnaces, and preparing the necessary heat treatment fixtures and other related elements is a rather complicated process. Naturally, factories aim to achieve the best results in the most cost-effective way possible. If there are no standard requirements, is it sufficient to provide assessments indicating that heat treatment is not necessary in order to proceed with welding?
The heat treatment of this material has no direct relation to whether it is a compressed part.
Is standard GB16507 applicable to this equipment?