A335 P91 Material Allowables

Hi all,
I am working on a steam system using ASME 31.1-2007. Using Caesar II 5.10.
The Pipe material is A335 P91. The temperature is 550 C (1022 F). At this temperature the allowable stress values are as follows.
Sc = 16753.9 N/sq.cm
Sh = 10540.5 N/sq.cm
As per code equation for allowable stress range Sa = f ( 1.25Sc + 0.25Sh ), the value should be Sa = 23577.5 N/sq.cm. But Caesar calculates the value as 19871.6 N/sq.cm. Please be informed that I am not using 'Liberal allowable stress' option in my file.
I also calculated the Sa value using material A335 P22 and the manually calculated Sa value matches with value calculated by Caesar. Also this calculation matches if I use the Code B31.3 in Caesar. So there is no problem with my Caesar file or configuration setup.
So why Caesar is calculating the Allowable stress range value different than the code equation, only for material A335 P91 if Code B31.1 is followed. Is there any specific clause or note mentioned in ASME 31.1 for calculating the allowable stress range for this particular material A335 P91??

Please reply
Thanks and regards.

Dear Experts,

Can somebody please see above query. This is a Genuine discrepancy occurring only for the material A335 P91, when used with Code ASME B31.1 only. I have checked the allowable in Caesar files of other old projects in our database. The difference comes only with A335 grade P91 only. The Stress range allowable value comes correct for grade P22 as per the equation.

Thanks

Guys,

Thanks a lot for your efforts. I got the answer in foot note 2 of ASME 31.1-2007 section 102.3.2

Regards

Zahid please let us know the solution in detail..
What was it exactly that you read. please post the text.

Basically, for setting the limit for expansion stress range, Sc and Sh cannot exceed 20ksi if the material tensile strength is greater than 70ksi.
(Dave Diehl corrected this post by changing "yield strength" to "tensile strength" - 9 July 2010)

Hey Dave
The if condition is for "tensile strength" and not for yield strength. The detailed answer is ...

The above mentioned foot note 2 says that if "tensile strength" of material is more than 70 ksi then the stress range shall be calculated using Sc or Sh value no greater than 20 ksi.

For material A335 P91 the tensile strength is 85 ksi. The Sc value in Table A-2 is 24.3 ksi which is more than 20 ksi.
Hence we need to use Sc = 20 ksi, that is 13789.5 N / sq cm
So Sa = (1.25 X 13789.5 + 0.25 X 10540.5 ) = 19872 N / sq. cm Which matches the Allowable stress value calculated by Caesar.

Zahid.

Zahid,

You are correct. I will update my post in case others do not see your note here.

Thanks.

Please, I am new in this soft.

How caesar II have account this point, Sa.
When I select A355 P91:
Sc= 167538.766 KPa
Sh= 115294.008 kPA (530ºC)

But I don´t have nothing option for change this value to 140 MPa, how the code indicate?

Fatetontube -

You should have started another thread for this post, your question has nothing to do with the current topic.

I believe you're asking about the computation of the Expansion Allowable? If so, check equations 1a and 1b in B31.3.