Problems with 2" Welding Neck Nozzles

[CuMo]

Dear Sirs,

I am new to this forum, so please excuse me in advance if this question has been discussed before. I cannot find the information needed whatsoever.

I am a total newby in vessel design (22 y.o.) so I am still experiencing difficulties in designing vessels.

OK. Here is the problem:

I am using Compress Codeware Build 6245 for designing a Water Drum with 10 nozzles. All nozzles calculation checks are being passed but one.

The problem is Nozzle T5 which is on the top of vessel and is mounted over Nozzle T3 which causes the following 2 errors in calculation data sheet:


WRC-107: Rm/t < 5 (ratio not covered by WRC-107; Rm/t = 5 used)
Rn/R ratio exceeds 0.7 so a U-2(g) analysis is required - see Appendix 1-7(c)

I cannot totaly understand what this error means, so I will be gratefull if someone helps me understanding the problem.

Is it the problem that the two nozzles T3 and T5 are the same size? 2"? I have no idea.

Please help me find a solution to this.

I am also posting 2 images with the configuration of vessel and the nozzles themselves.

Thank you in advance!

Best regards,
CuMo



direct link to image:

http://img393.imageshack.us/img393/8527/25299878qx2.jpg

direct link to image:

http://img393.imageshack.us/img393/4936/29131172ys9.jpg

 

[unclesyd]

The last two links show the T3,T5 arrangement.

 

[CuMo]

Exactly!
I just tried to post a thumbnail to the same image.

 

[jte]

CuMo-

The way I see it you have two options:

First (my preferred option), consider setting the code spec break on the stub of T3 below where T5 hits it. Presuming you are dealing with a VIII-1 to B31.3 transition, you make it very clear in your design doc's and drawings that the tee connection (since you would never consider a size-on-size fishmouth connection unless its ridiculously low pressure, right?) to the nozzle neck is where you are choosing to take your spec break. That's the first circumferential seam off of the shell, and perfectly legal. This makes the tee and remaining components above it "piping" which is legally much more easy to repair/alter in the field as compared to "vessel". Please... make my life easier! Of course, you'd still have the tee and flanges installed and hydro'd by the vessel fabricator. The hydro might have to be a bit higher to meet B31.3 requirements, but that is usually ok (doesn't cause issues with the vessel).

The second option is to just calculate the proper pipe schedule to use (you're already doing that for the nozzle neck) and specify a piping tee for that intersection. No additional calc's req'd. Ignore that Compress complains about the connection since you are manually specifying a standard piping component and not a tee built up from pipes.

jt

 

[CuMo]

Thank you, jt!
10x for wasting your time answering me. I had to read it three times since I am not native english speaker and at first I couldn't understand what exactly you mean by "fishmouth". But then I got it...

Whatever, I am sure this error is not fatal but wanted to make a research and see others' people oppinion.

You are right about the pressure. I think it is pretty low, but I can be 100% sure when I get back to work.

Either way our client has specified in preliminary datasheet that all nozzles marked "T" have loads. We may ask them reconsider these loads at this tee.
One way or another the company I work at is designer and vendor of these vessels

Thank you once again for consulting me!