Hello all,

Like the rest of us I'm writing in hopes of some guidance/understanding from the community.

In the results shown below you can see that my allowable stress is 39,453.3 psi which is higher than the required 35,000 psi SMYS of API 5L, Grade B (Appendix D). From a purely logical view this makes no sense to me.

So I’ve done some reading of B31.8 and found that para 833.5 allows you to go over yield, if strains are limited to 2%. My question is this: Is this the correct path to explaining the results? If not, can you please point me in the right direction?

The node in question is an underground section of straight pipeline. My L27 case you see is just T2 extracted via a L3-L25 operation (highest temperature). Since this is an underground section of pipe, the para 833.5 conditions starts to make some sense to me (well restrained pipe will thermally expand very little (2% or less). Is this logical thinking?

General parameters: 12” API 5L, grade B, standard schedule. Gas service,
Min Temp: 30 F Operating Pressure: 600 psi
Max Temp: 95 F (my T2)
Oper Temp: 66 F

I would appreciate your help on this.
Thank you!

CAESAR II results:

CODE STRESS CHECK PASSED : LOADCASE 27 (EXP) L27=L3-L25

Highest Stresses: (lb./sq.in.) LOADCASE 27 (EXP) L27=L3-L25
Ratio (%): 11.7 @Node 12015
Code Stress: 4601.6 Allowable Stress: 39453.3
Axial Stress: 604.6 @Node 10009
Bending Stress: 4601.6 @Node 12015
Torsion Stress: 190.8 @Node 10179
Hoop Stress: 0.0 @Node 12005
Max Stress Intensity: 4631.7 @Node 12015

The limit on allowable stress for restrainted pipe is something smaller than yield. The limit on allowable for pipe that is not (fully) restrained is based in ultimate strength and can exceed that yield value. Since your allowable stress is above yield, I have to think that CAESAR II has this as not (fully) restrained. You must select the proper radio button (below) to indicate this.

Yield does not necessarily mean failure. Yes, I shouldn't try to hang a 100 pound weight from a rope that yields at 50 pounds. That's what I would call a force-based load, and that's limited by yield.

But what of a paper clip? That functional device was formed - through yielding - from a straight wire into its current shape. Here, yielding is not failure. This is a strain-based load and such loads are limited by fatigue. These fatigue stress limits can be much higher than yield.

Dave,

Thank you for response and I understand what you are saying.

I just checked the radio button you mentioned and the option does not come up for node 12015. The option is available for the preceding node and I can confirm that the "yes" option is selected for what you highlighted above.

Also, this section of pipe was modeled using the underground pipe modeler that is included with CAESAR II. My understanding is that CAESAR II will calculate and add the required restrains. Isn't that why the option doesn't show up? If what you mentioned above is correct than I'm not sure what to do.

Thank you

To be more clear about what I mentioned above, the option is there but it is grayed out. It does show the node 12015 as restrained.

I have no quick answer here.
Please open a Support Request on Smart Support. Include your model file, the details provided here (at least by referencing this Forum post), and what version of CAESAR II you are running.