When piping, it is required that the spacing between welds be no less than the pipe diameter and no less than 100. What are the consequences if this spacing is too small?

Same question: sometimes there is really no space to run the pipes. Is it possible to weld the fittings directly to the flanges? Or weld a elbow tee?

According to the relevant provisions in the \"General Rules for the Design of Petrochemical Pipeline Layout\" (SH3012-2000), the center distance between two adjacent butt welds on a pipeline should be: for pipelines with a nominal diameter of less than 150 mm, this distance shall not be less than the outer diameter of the pipeline, nor shall it be less than 50 mm； b For pipes with a nominal diameter of 150 mm or greater, it shall not be less than 150 mm. This can be considered a fairly basic requirement; if the spacing between welds is too small, the mechanical properties of the welded joints will not meet the standards required for qualified pipes, and leaks are likely to occur at those joints. Furthermore, the local stress may also fail to meet the requirements, leading to easy damage and leakage. As for the issue of pipe fitting connections, the main consideration is whether it is convenient to inspect and remove the flanges after connection. Generally, pipe fittings with a nominal diameter of 50 or more are buttwelded pipe fittings, which can be welded to each other or to flanges.

I believe the spacing between welds is mainly determined by practicality in construction; for example, when workers cut pipes with a diameter of DN100 and a length of 50 mm, the resulting pieces resemble rings rather than proper pipes, which makes it difficult to weld them accurately, as well as to cut them precisely. Therefore, the spacing between welds should be larger; specifically, the \"General Rules for the Design of Petrochemical Pipeline Layout\" (SH3012-2000) should be followed

I remember that fittings such as tees should not have flanges welded directly to them; it seems that at least a 150-mm distance is required, although it isn’t stated that this rule doesn’t apply in special situations. However, for glue-piped systems, we have sometimes welded flanges to tees in order to reduce the length of dead ends, though this makes it inconvenient to remove the bolts. This post was last edited by Pseudo Xiao Bao on 2009-3-3 23:52]

What conditions are required for welding white steel?

Generally, elbows can be directly welded to flanges; I haven’t seen other pipe fittings welded directly to flanges yet

For pipelines made of common medium and low-pressure non-thermal media, it is feasible, in my opinion, to directly weld together fittings such as flanges, elbows, and tees, provided that the welding quality meets the required standards. This post was last edited by lisy on 2009-3-3 23:22]

Direct welding of pipe fittings is allowed for butt weld flanges, but not for slip weld flanges. It is common to weld pipe fittings directly to each other. As for the gap requirement between the two circumferential welds, it is **specified by the standards**. It is mainly to avoid the heat-affected zone during welding. But sometimes there is simply no space; ASME does not impose any strict requirements in this regard, and there are also no requirements for heat treatment after welding the pipes. Therefore, I have installed two DN400 pipes whose weld gaps were only around 50 MM.

I believe the requirement of 100 mm is to ensure that the weld spacing is greater than 3 times the heat-affected zone

I haven’t encountered this situation yet, but I still need to learn about it* to see how others handle it

The welding process is a high-temperature process that causes damage to the pipe. If the section is too short, its microstructure has actually changed, and it can no longer be considered a qualified pipe; its mechanical properties no longer meet the requirements of the manufacturing process.

Fittings are generally areas of stress concentration, and welding also creates such areas. Leaving a certain distance helps to avoid excessive stress concentration and prevent stress-induced failure； Moreover, if welding fails, and the fittings are welded directly to each other, the fittings will also be lost. So, follow the standard requirements.

The reasons for the decrease in mechanical properties in the heat-affected zone and welding stress.

A large-end and a small-end pipe can be directly welded to a flange, while a butt-welded elbow can be directly welded to a tee. An elbow cannot be directly welded to a flange; a straight pipe must be added

The original poster’s statement that \"the spacing between welds should not be less than the pipe diameter nor less than 100\" is likely based on experience or is a misinterpretation of the relevant rules. The full text is on the third floor; actually, standards 50235 and 50236 both address this issue. This is a standard for ensuring welding documentation, formulated in light of our country’s current level of steel pipe manufacturing and welding techniques. It mainly applies to self-managed sections; section 6.1.1.2 of 50236 states this \"except for welded and formed fittings.\" . . . . ” It is permissible to weld the flange directly to the elbow; however, in many cases due to practical environmental constraints, the required spacing cannot be maintained. In such situations, pre-weld heat treatment and other measures should be employed to prevent a decline in the mechanical properties of the heat-affected zone as well as the effects of welding stresses. For general low-pressure small pipes, the standards can be appropriately relaxed, but they should not be smaller than the pipe diameter.

Be careful of high temperatures and stress during welding! !

I won’t do it either; calculating the pipe spacing is quite complicated. Is there any good method?