Materials used for galvanized pipe fittings
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Materials used for galvanized pipe fittings: For 90-degree elbows used for instrument air with a DN50 size, why is Q235B with CL3000 grade used, while for sizes larger than DN80, 20# steel with SCH40 grade is used?
DN50 uses CL3000 because it is a threaded fitting; for threaded fittings, the strength grades CL2000, CL3000, and CL6000 are used. Using Q235B as the material is probably not appropriate – threaded fittings should be made of forgings rather than that material. Elbows larger than DN80 are extruded from pipes, so their wall thickness is also SCH40, the same as that of the pipes
I think what the original poster is concerned about is not the materials, but why threaded fittings are used for DN50 and butt-welded fittings for DN80.
Threaded fittings are better for galvanized pipes; welding will damage the galvanizing layer
I don’t understand what the original poster really means
We rarely do this in the projects we work on; galvanized pipes are more commonly used for instrument air, and installation is usually carried out on site. Fire protection piping is usually connected using clamps or flanged pipes. Is galvanizing done after prefabrication? Is this a common practice?
We use a lot of galvanized pipes for instrument air; construction is usually carried out on-site, with connections made using clamps or flanges, while threaded connections are used relatively less often.
For DN80 and above, it is also threaded rather than butt-welded; only the material and SCH standard differ
I think it’s been made clear enough – those above DN80 are also not welded
It’s indeed welded; I didn’t even understand:P