ASME Section 1 Steam Drum Nozzle Analysis via NozzlePRO (Section VIII Div 2)?

[Vulture860]

I'm working on a project where the vendor of an existing HRSG (BPVC Section 1) will not provide stated nozzle allowables for their steam drum connections. Instead they've provided the nozzle fabrication details (nozzle/shell materials, thickneses, repads, etc) for us to perform our own calculations. My question, can I utilize NozzlePRO software for these evaluations, considering they are performing calculations per BVPC Section VIII Div 2? I can't find specific reference in Section 1 allowing use of the Section VIII Div 2 calculations, but also cannot find reference for how to evaluate the loadings on these nozzles. Thoughts?

 

[A clark]

To answer your question, NO you cannot. All calculations must be performed in accordance with Section I PG-33. The nozzle loading as well look at PW-15. As this is an existing item, it must also meet the requirements of the NBIC. To my knowledge there is not a package program for Section I, Manufacturers usually have their own custom software or they do it manually. Also you should realize the Section VII Div 2 is a Code by analysis whereas Section I is a Code by prescription and experience. The two are normally not compatible.

If you are replacing the nozzle in kind the NBIC would consider it a repair.

Hope this helps.

 

[pdiculous963]

I think you could use NozzlePRO to evaluate the loads on the nozzles. PG-33 appears to just be the area replacement rules. As long as the rules of PG-33 are met, there is nothing wrong with using NozzlePRO to evaluate the stresses in the shell and nozzle due to piping loads. It is common to use the acceptance criteria of Sec. VIII-2 with the allowable stress of the original construction Code.

 

[Vulture860]

Thank you for the responses fellas. Interestingly, I've gotten Paulin (NozzlePRO) involved and they don't actually have a good answer for me as of yet. I'd understood that they don't see anything technically incorrect with this approach, however it's more of a code/legal issue as Section 1 simply does not give guidance here.

 

[pdiculous963]

I would imagine you are covered by PG-56.1(c) and PG-16.1. While PG-56 is for evaluating stresses due to structural attachments, PG-56.1(c) permits "other analytical methods as permitted by PG-16.1". PG-16.1 notes that there are not rules to cover all details of design, and that when rules are not provided, the design shall be as safe as the Code (essentially the same paragraph as U-2(g) in Sec. VIII-1). Since there are no rules to evaluate nozzle loads, by using NozzlePRO with the allowables from Section I, you are satisfying this requirement.

 

[A clark]

I have been reading the various replies with interest. I say again, you cannot use Section VIII Div 2 to calculate a nozzle in a section I PG 56 is for attachment on tube walls. It allows you to use tube membrane stress to carry load. All nozzles in Section I must meet all of the requirements of PG-37, PW-15 and PW 16 in addition to the area calculations. As an Inspector and Instructor, I would require manual calculations to prove the computer results, my recommendation is that you warm up your calculator and sharpen your pencil.

Section I also states that your can only use alternate methods only if Section I does not have formulas to cover the design. (PG16.1)

 

[pdiculous963]

Right, but PG-36 and PG-37 are for pressure design only. They do not address external nozzle loads (from attached piping), which would increase the stress in the vessel and nozzle. So the correct way to analyze a nozzle with external loads would be to:

1. Satisfy the area replacement requirements of PG-33 to validate the pressure design and comply with the Code rules
2. Analyze the stresses in the vessel in the nozzle using another technique. Typically this is done through using WRC 107/WRC 297 or using FEA (such as NozzlePRO). Since there are no rules on how to evaluate the stresses in the shell and nozzle due to external loads in the Code, this is acceptable per PG-16.1. Typically the calculated stresses are compared to the Sec. VIII-2 elastic criteria using the allowable stresses from the original Code.

The intent of this is not to design the nozzle using NozzlePRO, it is to validate the design with consideration for external loads, which are not accounted for in the Code equations.

 

[A clark]

I agree, It wasn't clear that they were calculating external loading.