Understanding alternate sustained load case in Caesar 2

[adilpervaiz]

Can anyone explain how to correctly interpret the alternate sustained load case in Caesar 2016 on wards. What significance it holds in the overall piping system and can we ignore this alternate sustained load case in any situation?

Secondly, with specific reference to a process piping example, I am analyzing a process piping which consists of high pressure steam (pressure 100 kg/cm2, temp 450 degree C) and alloy steel material. The results in Caesar software show that the piping stresses are high in alternate sustained load case, however, the stresses are within limits in both sustained and expansion load case.
Should i make any changes to the system to satisfy the alternate sustained load case also?

 

[StressGuy]

The answer is YES you need to make a change. The code requires that primary (SUS) stresses be evaluated while the pipe is in the operating state (i.e. at temperature). In practice, this meets that if a support lifts off due to thermal expansion, it isn't functional for the SUS stress evaluation.

The ALT SUS case now does what we used to have to do manually. Previously, you would make a stress run, look for Y supports that were positive (or 0 if you coded them as +Y). You would then go back into the model and delete those Y supports and make a new run. If your SUS stresses exceeded code, you would have to make changes, such as adding a spring support to insure that it remains active in operation.

Now, if you code supports as +Y, when Caesar runs the OPE case, it will check for uplift for you and automatically deactivate those support locations for the corresponding ALT SUS run. In your case, it reveals that you have inadequate support arrangement and are going to need to make changes in order to satisfy code requirements.

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.

 

[XL83NL]

Well put Edward. Good to see you back by the way. What took you?

 

[adilpervaiz]

Thanks Edward

 

[StressGuy]

Just been busy with work projects and family stuff. I had let checking in here slip out of my routine. I should be a more familiar face around here again.

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.

 

[XL83NL]

I should be a more familiar face around here again.

Given the number of LPSs you received, vs. post count, you sure are a good contributor to the site.

 

[KevinNZ]

Interest how B31.3 (2008) address this issue in Appendix P, but B31.1 does not.

 

[XL83NL]

Isnt this explained in appendix S of B31.3? Appendix P was withdrawn as it was considered to be unconservative