Does pipe welding allow small pipes to be inserted into larger pipes?
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As the title suggests, it involves a pipeline in which a 304 stainless steel DN200 pipe is inserted into a 20# steel DN250 pipe, and then the joints are welded together. Does the standard permit this welding method? Which standard contains a description on this? If permitted, does this type of welding fall under lap welding? The design pressure of the pipeline is 2.97 MPa, and the design temperature is 285. I seek guidance from experts in this field! ! ! Thank you! ! !
It’s definitely not standard; a reduced-diameter connection should be used instead.
I recall that in the project, DN200 fittings were welded to DN200 pipes without using tees; instead, holes were made directly and then welded there~ But both the fittings and the pipes were made of 304 material. I don’t understand why a tee isn’t used. . . I’ve never seen pipes made of different materials like this; I’ve only seen carbon steel and stainless steel pipes welded directly together. When welding different types of steel, high standards are required of the welder as well~
It is not recommended for use. This type of welding was indeed used in the past for desulfurization processes, but that was with carbon steel pipes of the same material, at very low design pressures and at room temperature. It might be acceptable for non-pressure pipes, but in your case the pressure and temperature are quite high, and it involves welding different types of materials. In any case, I don’t know how to use this method.
With these temperatures and pressures, even for the same material whole-body tees are not used; let alone welding different types of steel
Why not use standard fittings? If your calculation reports and welding procedure qualifications have been approved, it can be used.
The construction contractor did this to save money: the three connections require three welds, while the welding for opening holes requires just one weld
This phenomenon is quite common; things such as making holes in pressure test blind plates to connect pressure gauges seem to have been accepted by the general public
Reinforced calculation is required. Direct welding of dissimilar steels may cause electrochemical corrosion
A three-way standard fitting must be used; this is a typical case of poor quality
Maybe I didn’t explain it clearly enough; it’s not something like a tee joint, but rather similar to a sleeve, with a 250 mm inner diameter and a 200 mm outer diameter, joined by lap welding……