Hi,
I've been working w/ Caesar for about 8 months now, and doing pipe stress analysis for only a few months longer, so I know I'm not the most well versed in the subject - but my project manager and I can't figure out why we can't get these relief valves to pass code checks.

I'm using Caesar II 2016, 8.00.00.5600

I had set up my OCC load cases as per some guides I found on the subject, and each valve with the DLF releases with a downward force of 10k#. My load cases feature cases for either valve relieving, and then both relieving.

Now we know what our elbow is, as it's supplied by the valve vendor, and the inlet nozzle size is determined by our valve inlet, which is 3". Originally, we were supposed to use a 3" nominal, xxs pipe for the inlet, but our analysis is telling us it's failing miserably [400% or so]. We bumped the inlet up to a custom 4.5" OD - 3" ID pipe to try and beef it up, and we're still failing miserably.

Usually in this application/for this client [coal power], the relief valves are only supported by the inlet nozzle, as they stray away from dummy legs in high heat situations [1015degF].

The vendor is confident that they have installed these valves on similar lines in the past w/out issue, and hand calculations from B31.1 show that the stress should be just under code and not 400% of code.

I've had a few people in the office w/ more Caesar experience try to look at my model to see if there was something I was missing/doing wrong, but we can't figure it out.
I've tried modeling the inlet nozzle w/ a rigid element within the header as per some Caesar seminar notes my PM had from years ago - didn't make much of a difference.
The valves were initially at the upper leg of the model [reducing station], and we had similar issues.

I've made so many revisions to this model, and I'm just eating up our limited runs. Does anyone have any insight?

Please and thankyou for any help. I'm really hoping that there's just something stupid that my lack of experience is missing.

Looking further, I read something in the code that mentioned that typical branch connections are sometimes not enough to fully support a relief valve kicking on - It suggests adding extra reinforcement to the connection.

Is there any good way to model 'extra reinforcement?' I thought that all the branch connection details really mostly just affected the SIF, which I've already got pretty close to 1.

My quick calculation of stress on a heavy 4 inch pipe with a 20,000 ft-lbf moment is quite large. See below.

This thrust load, alone will exceed your sustained+occasional limit.

Do you see it differently?