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Factor in ASME B31.4

Factor in ASME B31.4

Factor in ASME B31.4

(OP)
Dear All,

Good Day!

I just want to ask regarding the Fac (Design Factor) in ASME B31.4 of CAESAR II. How to decide when to use 1,0,0.001? I only understand that in the pipeline underground the Fac=1 or 0.001, how about the pipeline aboveground? Thank you in advance.

Sincerely,
marchie

RE: Factor in ASME B31.4

I do not use CAESAR, but I can tell you,

There is no such design "1,0.001" factors mentioned in B31.4.
There are only stress allowables.
Example: Pressure stress due to internal-external pressure shall not exceed the pressure stress allowable (which in B31.4 is 0.72*SMYS).

How do your design factors relate to the stress allowables given in B31.4
What are you trying to analyze?

RE: Factor in ASME B31.4

If you read the help text it will explain the use of this factor. A value of 1.0 indicates to CAESAR II that the pipe is fully restrained. A value of 0.0 indicates the pipe element is unrestrained. A value of 0.001 indicates that the element's bi-linear restraint stiffnesses were setup by the Buried Pipe Modeler and the restrained/unrestrained status is determined by CAESAR II during the analysis of the individual load cases.

I always recommend that you use the Buried Pipe modeler and let CAESAR II determine the status on a per load case basis.

Richard Ay
Intergraph CAS

RE: Factor in ASME B31.4

Distance to the virtual anchor is critical. I recommend always checking the result manually.

RE: Factor in ASME B31.4

Hi Rich,
Thanks for the clarification. I do have a follow up question regarding "unrestrained" sections of buried pipe i.e. say at a buried segement close to the transition from A/G to U/G and with particular reference to elbows in this segment. Pipe code Canadian CSA Z662.
If we model the underground section using the underground modeler (and I assume this means CII uses FAC =0.001 by default)and as you say above "A value of 0.001 indicates that the element's bi-linear restraint stiffnesses were setup by the Buried Pipe Modeler and the restrained/unrestrained status is determined by CAESAR II during the analysis of the individual load cases.".
My question is for the unrestrained section, will CII compute the stress at the elbows as per combined stress per the partial restraint clause 4.7.2.1 i.e Sh - Sl + Sb by default ?
Or will the program compute depending on whether the net axial stress is compressive and then determine if the stress needs to be determined as per Cl. 4.8.4 of Z662 i.e. the expansion case : Sq. root (i Mb² + iMt²).
Thanks !

RE: Factor in ASME B31.4

Sounds like the OP is another Stress Engineer who can "operate" the Caesar software but does not really know what the program does!!!

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