Manifolds or headers questions

[ed72073]

Is there a rule of thumb for welding manifolds or headers that use compressed air? I am sure there is a simple answer, but I don't know where to look, that is why I am asking here. I have two size manifolds that I need to fabricate, but I am think it needs to be done by a certified shop. These are 3"x 3" x 36" tubes 1/4" wall that will have six 1/2" NPT couplings, and two 1" couplings welded to the tube. There will also be a supply end that is 2-1/2" and mounting brackets to attach to a machine. The other would be 6 'x 6" x 54" tube 1/4" wall with three 1-1/2" NPT couplings and a supply and petcock.

I guess what I am asking is there a formula that is used to figure if these are to meet ASME standard or is this exempt from ASME?

 

[metengr]

Look at ASME B31.3 for design information.

 

[marty007]

What is the design pressure/temperature?

 

[ed72073]

The design pressure is main supply that is usually 100psi. and the temp would just be atmospheric, if this answers your questions correct.

 

[davefitz]

I think if a 54" pneumatic manifold were to let go in a shop, there would be one heck of a medical bill. A couple of tombstones, too.
Some shops , companies, and insurance underwrites require that if the vessel operates above 15 psig, it will need an ASME stamp, or at least some proof that it was designed , fabricated and tested per ASME requirements. For the 54" manifold, a hydrotest at 130% max expected operating pressure would certainly be needed.

"Whom the gods would destroy, they first make mad "

 

[ed72073]

I understand the extreme dangers involved, and not being ASME certified this is why I was asking. If the headers need to be make then I am going to have the made proper, but ultimately that will be the decision of the customer. I can't believe the amount of people that I deal with have no regard to the safety issues, and these are people that deal with pressure vessels all the time.

 

[davefitz]

ed72073

I understand completely- I have seen fab shops that fabricate their own compressed air manifolds on the spot with no design check, no QC, no hydrotest.It happens frequently. But when you get to 54", it is necessary to get it right.

"Whom the gods would destroy, they first make mad "

 

[MJCronin]

"The other would be 6 'x 6" x 54" tube 1/4" wall with three 1-1/2" NPT couplings and a supply and petcock."


Is there a typo here ?

Why would you not use a pre-certified commercial grade item ?

http://hansontank.us/airtanks.html

MJCronin
Sr. Process Engineer

 

[ed72073]

No that is not a typo. A pre- certified header would be fast and easy, the only issue is where the couplings or position of the couplings are located. To mount up to an existing piping the coupling need to be laid out for each header. The piping is welded through a plate and there is nothing exact about it, each pipe with a union is at a different height, and distance. If I use a straight edge across the three unions, there are slight different angles to each.

The think is to either cut the pipes free and get everything inline, then make a template to shoe position of each coupling. The customer is feeling this is just to much thinking and amount of work. They have made their own manifolds in the past, but there is some reason why they are not now that I don't know of. My feeling is to have a certified shop make everything or to just stay away from that job.

If you think this is bad, look at my other post about Pressure Vessels alterations

http://www.eng-tips.com/viewthread.cfm?qid=385044

 

[GenB]

First when you say 3x3and 6x6 seams that you are using square tube. If pstd pipe is used the minium required is sch40 and as long as a certified weld lrocedures and certified welders are used. Most jurisdictikns will aproove the jobs. Non AZME work but owner user. Best consult the loc Km budi.g,mechanical inspector for approval. Other than that a certified shop can build the header and the outlets done on site since small oleni.gs may be excempt From Inspection.I ha e seen many accidents with compressed air And I wouldn't take a chance.