We have below mentioned query about WRC analysis.

“We refer to nozzle loads calculations as per WRC 107 in PV ELITE. Please note that as per Client job specification, pressure stress indices shall be considered as per ASME Sec. VIII Div.2 while calculating the stresses due to pressure for all nozzles irrespective of presence of cyclic service/fatigue requirement. These stress indices shall be considered for analysis at nozzle to shell junction and need not to be considered at edge of pad analysis.”

Please advise how to comply above CLIENT requirement with PV ELITE software (any option available to define PRESSURE STRESS INDICES)? How to take care of this PRESSURE STRESS INDICES in the design? Any guideline/ info, which you can provide on this subject?


As we have to perform/ design number of Vessels for the plant having this requirement, your positive response will help us.

Best Regards,
Sunil Agrawal
Chief Engr (Mech)

Tecnimont ICB Pvt Ltd

Hello Sunil,

I have performed this kind of activity for pressure stress indices using Nozzle Pro and not PV Elite.
basically if i understand well it states customer does not require pad analysis and junction FEA, however clearly requires nozzle to shell junction analysis.

Hello Sunil Agarwal,

How do you solve your query?

Regards
ASD23789

Dear Mr Sunil Agrawal and others
It is Srinivasan here from ISGEC. Yes this is an important problem.
In some enquiries , we have discussed and resolved with client. In some cases we have taken alternate rule of PD5500 (if spec permits the same.
The code clearly mentions that incorporating the stress indices is to get peak stresses. Please refer 5.D.1.1 of Annex 5.D which states that the stress indices may be used to determine peak stresses around opening. If we click stress indices, what we are computing is PL+Pb+Q+F. Do the spec wants us to check this as PL+Pb+Q (sps = 3s or 2 yield ?).
This is same as limiting the surface stress for 3S instead of linearizing the SCL in FEA.
I want to understand the background and have also raised this in the forum.
Hope one day we will resolve / understand this

With regards
srinivasan

Please refer to my post in May 2010 and replied by many including Mr Mandeep Singh and our friends from L&T, Tema etc; Also refer to Mr Mukesh Chopra's response and reference to EIL spec. note no.5.

I understand some more spec also ask for the same. We shall discuss and understand and clarify this issue once for all

Regards

R.SRINIVASAN

Dear Mr Srinivasan
I red your post of May 2010, and I agree with you; I am working on vessel design with a client spec. requiring same calculation as posted by Mr Sunil Agrawal in first post;
I found a compromise with my client, using allowable stress from table 2A instead 1A, that are greater for low temp., and using operating load instead of design load.

Regards
Umberto

I think the real problem is the consideration of the pressure stress at the opening. The client wants to consider the effect of stress concentration due to opening. If you apply Pressure stress indices then you get the effect of the opening as well as the peak stress due to presence of the welding. This is very conservative, as pointed by Mr. Srinivasan, this gives Pm+Pl+Q+F. Then, you need to compute cycle life for fatigue.

You really need PL (local primary) stress due to pressure at the opening. May be Appendix 1-10 can be used to get PL and then that can be used for pressure stress instead of Pm (membrane pressure stress) currently in WRC-107?

Then, you do not have to include pressure stress indices. But, you only have 1 PL value at the opening and not at 4 points around the nozzle as in WRC-107. So, it will be conservatively added to WRC-107 stresses around the nozzle.

What do you guys think? Looking forward to your feedback.