I have a Pressure relief header to run in a plant.
Problem is time! we need to reduce the analysis time to a minimum.

By experiance, the laterally (45degrees) swept stab-in inlets to the relief headers can usually require re-pads.

So that i can reduce the analysis time, i intend to up the run pipe schedule from sch10s to sch40s hence eliminating the repetative addition of repads.

A engineer here has discounted this by stating it is not possible to weld a sch10s branch to a sch40s header.

I'm no welding engineer, but every stress engineer i have worked with regulally uses this trick to reduce work on the main prv headers.

So my question is: is it within engineering reason to do this??
The header is 12" and the run pipes range from 2"to10"

I've looked at the code (B31.3) and i can't find anything to discount it.

Regards Tim.


oh and my apolagies to the welding Eng's if this is a dumb question.!!

Your question needs to give us the material.....

Heres what is in play.... when you weld you melt metal... the header, the branch and the filler metal. In the case of the thinner wall section there is less metal mass to accept the heat of the puddle of molten metal so it will have a tendency to "burn" through.

Different metals have different welding characteristics as well as heat conduction and betweeen these two factors they may make a great enough difference to either preclude or exclude weld burn through of the the thinner wall section. I have a friend who is a welding engineer so when you post your materials I will email him for an answer....

.....and you also warp the schedule 10 metal around the heat affected zone so it is hard to keep the schedule 10 metal from deforming. Since you are making angled (lateral) connections you have a difficult fit-up and alignment (intersecting ellipses). When the schedule 10 metal local to the intersection of the cylinders warps it is tough the keep the correct fit-up for complete fusion. It is not impossible to do it but it will give the welders a challenge.

You have to remember pipe is not very often "round" when it is delivered to site (hollow most of the time, but not round).

I had to deal with a client who wanted to fab up 45 deg laterals from Sch 80 CS pipe. His welders had a great deal of trouble geting good welds in the crotch area. This is not surprising - the standard weld bevel is > 22.5 degrees, so it required some tinkering before they could get a weld to pass X-ray.

And you're trying to do this with Sch 10S branches. Good luck!!

You should consider making the lateral out of all Sch 40 and making the Sch 40 to Sch 10 transition on the butt weld at the other end of the branch out of the lateral. This will make the welding of the lateral a relatively much easier chore.

I like Craigs suggestion!!! The wall transistions can easily be turned on a lathe!!!