Flanges on headers

bob young

screwed flanges are usually used with screw pipe. when you weld the header , you do not usually need or use flanges. i much prefer flanges as opposed to unions on pipe 2 " & larger . a lot of mechanics do not use flanges because it takes piping skill to a higher level but it is a much better job.

Bill_110

Flanges on headers

Thanks in advance for answering my entry level questions. I notice that in a lot of the boiler installation pictures done with black iron pipe that the header sections are joined with a flange. Looking in the wikipedia flange definition it mentions these are usually welded but can be threaded. The installation manual for my boiler states headers shall not be welded. I'm wondering what the pros and cons of each method are? I assume the prohibition against welding has something to do with expansion and contraction problems?

bob_46

Flange

The coefficient of expansion for iron (the boiler) is approximately .000006 and for steel (the header) it's .000007. You can see that the boiler is going to expand less than the header. Sumpthins gotta give. A screwed header, especially one with swing joints is much more flexible than a welded header. I don't think welded flanges would be much of a problem if the rest of the header was screwed.

[Deleted User]

One of the reasons I heard in favor of flange unions is they have a smoother flow than a regular union and therefor less chance of water hammer?

bob young

flanges

untrue . they will not leak or seep due to vibration or expansion & contraction movement. a more positive connection