Dear all.

I would be grateful if someone can help with this doubt about stress results in underground pipeline.

My question is related to how Caesar II calculate Stress Equivalent in Restrained areas (B31.4 402.7 Combining of Stresses Seq). Applying the formula Seq=sqrt(SH^2-SH*SL+SL^2+3St^2) we obtain different values than from Caesar II Output Stresses (Multiple Code/Allow) Comb column. Indeed, it seems that Caesar II divides the result between 0.875, but this as far as I am concerned, does not apply on Seq calculation, it is already included on the 0.9 SMYS of the Comb Allowable.

Resuming, it seems that Caesar II is applying the mill tolerance factor on Seq, and from my point of view it should only be imposed on Comb Allow through 0.9 factor over SMYS.

Thanks in advance.

That doesn't sound right. Check to make sure your analysis isn't using the first equation in Paragraph 402.7.

If you can't resolve the issue, open an SR on Smart Support.

First of all, thanks a lot for your prompt response Richard.

I would like to share my values just in case any help could arise:

A358 316
Elastic Modulus E(MPa)195100
Exp coef (mm/mmm/C) 0.0000156
Diameter: 323.8mm
Thickness= 21.44mm
T1= 25C
T2= 55C
Pressure = 152bar
Yield Stress= 207MPa

Results obtained in a RESTRAINED section UG B31.4:

SThermal (MPa) SE = E*ALPHA*(T1-T2) Formula: -91.3; Caesar II output: -96.0
SHoop (MPa ) SH=Pi(D-t)/20t Formula: 107.2; Caesar II output: 107.2
Long (MPa) SL=SE+vSH+M/Z+Fa/A Formula: -59.2; Caesar II output: -64.7
Seq=sqrt(SHsqr2-SHSL+SLsqr2+3Stsqr2) Formula: 146.0; Caesar II output: 171.9

Comb. Allow. (MPa) Formula: 186.3; Caesar II output: 186.3

So we do not understand how Caesar II calculates de Stress Equivalent values (Comb & Code) for this particular case. The difference is about 15% for the hot case.

Thanks again.

Please see the attached MathCad PDF which shows where the numbers come from. This is from the CAESAR II Tech Support group.