Discussion on the groove issue for flat welding flanges?
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Regarding the groove for butt-welded flanges as specified in HG/T20592-09, that is, the groove at the junction of the flange and the pipe is at 50 degrees. I have a few questions; I would appreciate it if experts could share their insights 1) How was this flange groove specified by the Ministry of Chemical Industry? Is it too conservative? 2) The groove here is of a non-thoroughly welded structure; my understanding is that as long as it facilitates welding, an angle of at least 50 degrees is not necessary. 3) Additionally, if the pipe wall is thin, especially in cases of welding different materials together, a large amount of welding work not only increases the labor intensity associated with welding but also tends to cause welding deformation. I would like to ask those with experience: how do you handle this in practice?
1) Conservative； 2) Ensure that the cross-sectional area of the weld meets the required standard ； 3) Thin pipes are prone to damaging the mother structure, and deformation is inevitable. For thin-walled tube welding, it is sufficient to control the current level.
If the pipe wall is thin, especially in cases of welding different materials together, a large amount of welding work not only increases the labor intensity associated with welding but also tends to cause welding deformation; our factory handles such tasks carelessly
Recently, a batch of low-pressure stainless steel equipment we had also encountered this issue. The cylinder thickness was only 8 mm, and the equipment flanges were purchased as finished products with pre-made grooves. During assembly and welding, significant deformation was observed; there was no other option but to use electrodes with a smaller diameter in order to reduce the heat input during welding and to carry out symmetric welding. Still, deformation couldn’t be completely avoided, though it remained within acceptable limits. Ultimately, no leaks were detected during the hydraulic testing of the equipment.
I believe that the value of b for the groove in butt-welded flanges as specified in HG/T20592 is advisory in nature; the recommended value of b does not take into account the s value of the pipe wall. The effective height of the fillet weld section should be 0.7 times that of the thinner component, so I think it is appropriate to set the height of the weld angle equal to the thickness of the pipe wall.