Valve and pipeline welding issues
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Where should the cutting position be when replacing a welded valve? Should the original weld joint be cut off as well? If the distance is not sufficient, take over control again; then how should one determine the distance between these two welds? Are there any standards in this area? Please give me some advice~ Thank you~
Butt-welded valves, or socket-welded valves? There is a fundamental difference between the two. For butt-welded valves, the weld is a lap joint weld, and there are requirements regarding the spacing between the two welds, as specified in SH3501. When replacing the valve, simply cut at the weld site and then weld it again. In the case of socket-welded valves, the weld is a fillet weld; there is no restriction on the length of the weld – it just needs to be long enough. If it isn’t long enough, an additional section can be added, resulting in only one weld seam in total.
Is the cutting in place done without considering the heat-affected zone from previous welding?
For butt welding, the original weld joint is usually chosen. . In this way, the distance from these can be precisely controlled. .
You can check pages 14-15 of SH 3501-2011; what you’re referring to is likely socket-welded valves. The common practice on site is to make an angled cut inward along the location of the original weld. Since the old valve is no longer needed, and the sections of the existing pipe that are inserted suffer more from heat effects, plus small pipes generally have greater expansion/contraction rates, it’s not necessary to add an additional section of pipe – instead, the pipe is simply cut open, polished clean, and then inserted for welding. All the craftsmen working on site know how to do it. Haha:D