Pipe line specification

[pipe15]

We have a situation where the stress analysis requires a heavier pipe schedule than the design pressure and temperature of the line would require. The system is a Class 600 system (flange and valve rating per 16.5 and 16.34). the application is for a safety valve/rupture disc pipe layout. The pipe, in order to meet the design conditions, would be schedule 40. the stress analysis requires the pipe to be schedule 160.

How should we handle this with regard to the piping material specification document?

My solution is:
We are using Intergraph's PDS system to model the pipe, and I would just like to make the default schedule in that class to be what is required for stress considerations, with the lower schedule in as an option. The appropriate notes would be included in the pipe spec to describe where the heavier wall thickness is to be used.

Another alternate solution would be to have multiple class breaks on the P&ID to show that the flanges for the safety valve outlet and rupture disc are the appropriate Class 600 spec, and the piping would be labeled with a separate pipe class that has the required pipe wall based on the higher design conditions of that class. This way is more cumbersome, but does not leave anything to chance regarding the selection of the proper pipe schedules.

what does anyone else think?
thanks
Mark

 

[unclesyd]

Can you give a few more details on your system as a change from Sch 40 to Sch 160 pipe is one big step change especially for a Class 600 flange call out.

 

[Latexman]

I think the P&ID method should dictate whats on the pipe model.

Good luck,
Latexman

 

[BigInch]

I don't see the need for a separate pipe class as they always seem to be based primarily on pressure and temperature. This situation is not new and doesn't require a new procedure. Just treat it in the traditional manner. Besides, if you start creating a special class for all the nontypical situations you will encounter, look out... you're going to have an unmanageable number of classes very soon.

I would use the default mode set to pressure and temperature wall thickness in the specification, with the additional note, "unless noted on drawing". On the drawings, which almost always take precedence over the specification (check contract), you make the note,

"Class <X>, schedule <xx>, unless noted."

Then make the appropriate notation at the specific locations where the XXH wall is required on the drawing.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[pennpiper]

Your problem seems to be a bad conclusion to a stress analysis.
First-
At the very least, make that stress engineer justify the change to Sch 160. And when I say justify I mean really justify it.

Second-
I would get a new Stress Engineer.

 

[BigInch]

He's obviously got a mainline axial anchor 40 ft out on the blowoff line.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[pipe15]

I guess I will have to elaborate on this issue a bit more.

the safety valve in question is at the top of the pressurizer in a nuc plant. the valve is ASME Class 1 inlet and ASME Class 3 outlet. the class 1 piping must also meet various LBB criteria (Leak Before Break). Being at the top of the pressurizer, the seismic response spectra is about as high as it gets in terms of g values for the plant piping.

And yes, BigInch, you are correct, there is an an anchor on the 10" vertical riser off of the safety valve. Your comment above "Class <X>, schedule <xx>, unless noted." is also good and would be like the solution I had proposed.

The original guestion is concerned with investigating methods of documentation when specifying pipe with heavier wall than design conditions would warrant in the pipe spec document.

 

[BigInch]

That's the only reasonable answer you could have given.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com