Subject: Allowable Expansion Stress Range for A790 S31803, A790 S32760, API-5L X52 not as per B31.3 Code.

Caesar-II Version using : 7.00.01.1600, (Build 141003).

Hot and cold allowable stress data for subject materials are showing correctly in the input listing but during code compliance as per B31.3 , expansion stress range allowable showing same value of 206.8427 Mpa for all above three material. Liberal stress flag is OFF.

Attached sample system for DN250 lines of different material @150 deg C.
Please review and let us know where we are missing something.

The 2012 Edition of B31.3 placed an upper limit on Sc and Sh used in the expansion stress range allowable stress. These values cannot exceed 138 MPa (20ksi).
Sc and Sh are typically based on a fraction of yield or tensile strength. Since higher strength steels have not shown a similar increase in fatigue strength, the Code's fatigue check removes that overage.
Maximum expansion stress range using (1a), then, is 1.5(138)= 207 MPa

Dave,

Thanks for the response. Sorry, still I am not able to get the point. Let clear my understanding...

For A790 S31803 at temp 150 deg C as per B31.3

SC = 206.842 MPa and SH= 199.107 MPa, therfore expansion allowable supposed to be SE = 1.25Sc+0.25Sh ( considering f=1.0) = 308.33 Mpa.

Now the Caesar-II 2014 Ver 7.00.01.1600, (Build 141003) showing this SE value as 206.8427 MPa whereas it is using correct SH value (i.e.206.842 Mpa) during sustain check.

I checked in Caesar-2011 ver 5.30.01 (build 120131), the SE values are coming as 308.33 Mpa as per code calculation.

As you explained, Sh and and Sc can not go beyond 138 Mpa and thus SE<= 207 Mpa even if for higher strength steel like DSS, SDSS material, I checked in B31.3 2012 and the equation for 1(a) still the same but I did not able to find the statement where code is limiting the values of Sc and Sh within 20ksi. It will be great help if you can provide page or clause reference.

Sorry Dave,
I found it in B31.3 2012.(Page-17)
Sc and Sh can not be taken more than 138Mpa for displacement stress range check.

It is a big change. Most off the existing piping system show failure.
I am doing a brownfield project which have been done on Caesar-II 2011 version. Now the system showing failure. I am in trouble now !!!

Thanks for your help.

Regards

Depending on your material you might get some relief by bumping f up to 1.2. Read the rules of applying f in that same section of the Code.