In one of the projects, I saw the following load case has been used for ocassional case.

W+P+U1
W+P+Win1
for seismic and wind loading respectively.

Generally we use the following combination

L1 W+P+T1
L2 W+P
L3 W+P+T1+U1
L4 L3-L1
L5 L4+L2 (scalar)for occasional loads

Which combination is correct?

Thanks

MW

Is L2 in your example the alternate sustained? I've always added the occasional load back to the regular sustained case and just checked the alternate sustained to make sure nothing failed or was excessive.

I would say the first example is wrong because the occasional loads need to be considered in conjunction with the normal operating condition, including temperature. Then you have all the load case algebra to isolate and analyze that occasional load for pipe stress purposes.

For the wind case, its possible they're assuming the plant was shut down in advance of a hurricane and so the only loads were weight/pressure. But they still need the additional load cases to isolate/add back the occasional component.

For seismic you can't assume the plant has advance notice to shutdown.

If you're working with ASME B31.3, then the second set of load cases is what's required by code.

I couldn't say with certainty that's how all past, present, or future codes have worked / currently work / will work.

Hi all,

Michael its right, the second loads set is the correct one. This is valid for ASME B31.1 / ASME B31.3 Codes.

The B.31.1/31.3 provisions which require this approach are old enough (definitely they were in role twenty years ago...) and I am really surprised that such elementary issue still raises doubts among stress engineers.

Regarding B31.3 - see Para. 302.3.6:

<<...THE SUM OF THE STRESSES due to sustained loads, such as pressure and
weight, SL, AND OF THE STRESSES produced by occasional loads, such as wind and earthquake, may be as much as 1.33 times the basic allowable stress provided in Table A-1 or Table A-1M at the metal temperature for
the occasional condition being considered...>>

So, it is NOT written "the sum of the stresses due to sustained and occasional loads". This means that the absolute values' summation of the longitudinal stresses devloped bu SUS and exclusive OCC loads needs to be checked against Code allowable limit. There is NO ALGEBRAIC summation to be performed.


In B31.1 the formulation is slightly different, but with the same meaning - see Para. 102.3.3:
<< The SUM OF THE LONGITUDINAL STRESSES produced by internal pressure, live and dead loads, AND THOSE produced by such occasional loads as the temporary supporting of extra weight may exceed the allowable stress values given in the Allowable Stress Tables by the amounts and durations of time
given in para. 104.8.2.>>

In B31.1, the absolute summation is clearly documented by formulas (15) and (16), which stipulates the summation of the BENDING STRESS terms corresponding to SUS and exclusive Occasional loads.

I repeat, these are elementary issues for Piping Stress Engineers involved in onshore or offshore topside PIPING systems.

For offshore Pipeline systems (B31.4/B31.8), as I remember briefly (I am not frequently involved in such projects...), the approach is different. Maybe another Forum member with current/extensive Offshore Pipeline analysis experience may complete these considerations.

Regards,

Agreed 100%.
I joined a new company a couple of days ago and I saw them using the first set of load cases. They have been using this for a number of years. I tried to discuss with my colleague but it took some effort to convince him. I asked this question in the forum to show him what most people do and think about these cases. its not easy to change old practices especially when you are new in a company.

Regards

M. Waheed

Yikes, that's not a good first impression from the company.

"This is what the creators of the software instruct us to do. These folks also serve (or at least used to serve) as members of the committee for the ASME piping code. I strongly recommend that we adhere to their instruction, as I'm sure they're very certain on the intent on the application of this piping code in their software."

It is in their documentation here:
https://docs.hexagonppm.com/reader/O04dxcwMfibZIK1cyksZvQ/y8mPw1Z_BdQYjgU1fqz93g

And per their instruction here:

https://coade.typepad.com/coadeinsider/2010/06/caesar-ii-webinar-load-case-editor.html

As well as a document floating around named "895-387-LoadCases.pdf," that you can find on the forums and via google, which seems it's from COADE, but I can't authenticate that.