Calculating Wall thickness of Piping components

[Phemmy47]

I've got ANSI 31.3 barred tee fittings while the pipe is ANSI 31.8 and 31.4. I need to make the wall thk compatible for the same pressure rating and hydrotest pressure. How do I go about calculating the required wall thickness for the barred tees?

 

[0707]

My understanding is that you have to purchase the barred tees with a schedule thickness bevels compatible with your pipes.

 

[NozzleTwister]

I don't quite understand your statement, "I've got ANSI 31.3 barred tee fittings while the pipe is ANSI 31.8 and 31.4."

You need to determine which piping code has jurisdiction over your system, B31.3, B31.4 or B31.8, and calculate the required wall thicknesses of your pipe and fittings (tees & elbows) using the equations and allowable stress values from the appropriate code.

If you are using a higher strength Line Pipe with lower strength Fittings, then your fittings will require a thicker wall. If that's the case, you DO NOT WANT TO BEVEL OR TAPER BORE the fitting to match the pipe. If the fitting is weaker, you need to maintain full fitting thickness for all of the fitting. B31.4-2002, Fig. 434.8.6(a)-(2) detail (c) shows an example of a butt-weld that you would use that will maintain full strength in the weaker component.


NozzleTwister
Houston, Texas

 

[zdas04]

Recently I did all the thickness calcs for a compressor station as B31.8. The client came back and said that regardless of intrepreation, every site they built with a fence around it was B31.3 so I redid the calcs--I got exactly the same required wall thickness using the more complex arithmetic of B31.3. As NozzleTwister points out, the system needs to be built to a specific code, but the same fitting will often work in any of the B31 family of codes. Pick one and run the calcs for your tee and see if it works. It probably will.

David

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

The harder I work, the luckier I seem

 

[Phemmy47]

For a Piping system of ASME B31.3, how do I obtain the required wall tickness of an 8" barred tee?

 

[NozzleTwister]

Phemmy47,

You obtain the required wall thickness by using the wall thickness equations in ASME B31.3. The barred tee would be no different than any other tee.

Your original post stated you were using this tee in B31.4 or B31.8 service. If that's the case, the equations in the the code that covers your system would apply and not B31.3.

You will receive better responses with a more accurate picture of what you are really tring to do.

Regards,

NozzleTwister
Houston, Texas

 

[11echo]

OK, I have to ask ...Why would you not "match" the schedule of the pipe this barred tee is going on? I've never heard of intentionally mis-matching the schedules of your components, unless you where trying to make use of existing items!?? …"IF" you did do this you would need to back taper the ends of your tee to match the schedule of your pipe. Seems to me to be alot of extra work!?? ...Mark

 

[NozzleTwister]

11echo,

This thread hasn't made sense to me since the beginning.

I don't understand why the tee will be a different code as the adjacent pipe. For me, this is an unusual place for a code change.

Basically your right 11echo, but there are several things that can give you mismatch.

Sometimes in pipeline systems, high strength pipe is used with fittings of a lesser strength which require a thicker wall.

Also, if there is a change in code jurisdiction, the differing equations will yield differing results.

I want to caution that when matching high strength pipe with lower strength fittings, you DO NOT want to taper bore the fitting to match the pipe. Refer to the weld details in the codes for alternatives.


NozzleTwister
Houston, Texas

 

[11echo]

Nozzle Twister,

"IF" you didn't back taper the bore you could have problems with either the flow or trying to get a pig to pass thru your line (depending on the type of pig you’re using). I see your point about using fitting with different yield strength, but that would be kinda "tricky" engineering and I don't think you could classify that as "good practice". I'm calking this one up to a "green" engineer myself! *G* ...Mark