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operating case allowable stress

operating case allowable stress

(OP)
I am conducting a flexibility stress analysis  on a superheated steam pipe designed at 525 deg C and 110 bar.

The computations are done following the B31.1 code.

I have encouterded some problems in finding the theory and formulas behind computations the software does in the operating case (weight+pressure+temperature).

Does anyone know how the program does this computations, and which is the routine behind results?

How is computed the allowable stress in the operating case?

RE: operating case allowable stress

B31.1 does not consider the Operating load case a "stress compliance case", and therefore provides no equation for the allowable stress.  This is why CAESAR II reports the allowable as zero.

For B31.1, the "stress compliance cases" are: Sustained, Expansion, and Occasional if you have that load set.  You need the Operating case for structural loads, overall displacement limits, and as a component to the Expansion case determination.  However, the mechanical stresses determined for this load case are not "Code" stresses and therefore are not used in any sort of pass/fail criterion.

Richard Ay
COADE, Inc.

RE: operating case allowable stress

(OP)
Thank you very much sir.

RE: operating case allowable stress

codrutdan,
          Pardon me pointing this out but if you are not sure about the computations the software performs in its analysis should you really be analysing superheated steam pipework at 525 Deg C and 110 Bar ? Without knowing the how the program works can be dangerous as you will always get results but are they accurate.

RE: operating case allowable stress

(OP)
Hmmm,

Somebody said to me once that "0" is the best beginning...

You are right,assuming responsibility for such an application in "my position" (no expertize whatsoever in the field of stress analysis), would be at least a proof of great suicidal courage.

This pipe line that has been operating for 40 years(and whom the owners want to keep in production)is a virtually wreck and at the moment we are in a process of verifying its structural integrity, starting from diagnosis of welds and corrosion verification by UT, etc.

The question mark that risen our endeavor to step into the intricate and judicious jungle of ASME (in the absence of the initial design documentation)was how do we now that the supports are good.

We have learned a lot in the meantime and i think we have managed to reach a point where we can actually use the output data from CAESAR to answer this question and also to redesign some of the supports.
Kind regards, Codrut

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