Nozzles Attached on Elliptical Head 2

[StressFreak]

Hi,

I had a discussion with my collegue at work because he thinks that the nozzles attached to an elliptical head must be placed inside a circle of diam = 0.8 Head's OD.

Refering to the ASME code UG-37, I only found that in case the nozzles (with their reinf pad) are included in a 0.8*(Head's OD) circle, then the required thickness of the shell for reinf. calculation would be of that of an spherical head with a corresponding coef. depending on the radius relation of the ellipse.

Since he's a 60 year old man with a lot of experience on PV design and I'm new in this subject, I'm not sure if he's right or wrong.

Can anyone give me his personal opinion?

PS: Sorry, I published the same thread in the piping forum.

 

[prex]

thread794-159433
Please do not cross post.

prex

http://www.xcalcs.com

Online tools for structural design

 

[jte]

Me thinks you meant this one: thread378-162942

jt

 

[rhg]

You can attach the nozzle outside a circle of 0,8D and "tr" shall be calculated accordingly.

A lot of years is not equal to "good experience"

Regards
rhg

 

[SnTMan]

StressFreak, there is a fairly large body of opinion that a nozzle should not be placed outside the 80% limit. As I posted (partially) in another thread:

"... my interpretation has been that there are no specific requirements in the Code when the nozzle and its reinforcement fall outside the 80% limit, i.e. is is a U-2 (g) design, therefore I tend to avoid placing nozzles out there."

It is kind of a question of what you can justify to customers and AI's, and many "old guys" avoid the practice.

As asked, this is my personal opinion.

Regards,

Mike

 

[StressFreak]

Thank you very much for your fast replies. I think SnTMan is right about "what can you justify to customers". I personally think that since verifying this through finite elements is something not so easy, old guys tend to stay on the safe side and simply not go for this alternative.

 

[prex]

StressFreak,
in your OP you wrote '...must be placed inside...': if you use that wording, then the answer is 'No, you are not obliged by code to do so'.
If you have the choice, then of course there is no reason to place a nozzle with part (or all) of its reinforcement outside that circle. The point is that sometimes you need to do so.

prex

http://www.xcalcs.com

Online tools for structural design

 

[unclesyd]

We have numerous SS reaction vessels where a nozzle is placed as close to the edge of the head as possible. The reason for this is the nozzle is a manway and the vessels have to be entered using a rope ladder for inspection and repair and they are suspended 30' above the floor. If you are the one entering it is awful nice having the ladder next to the wall. The reinforcing pads are formed to fit the adjacent head contour.
The vessels 12' dia, 16' lg, are designed for FV & 100 psig @ 150°C. There has never been any questions during numerous repairs under the auspices of several AIs' and insurance audits.
The calculations for the original vessels was by hand and when an FEA was done the stresses were within 5% of the calculated around the nozzle.

 

[SnTMan]

The only "grey area" seems to be how to calulate tr when outside the 80% limit. It would appear permissible to use UG-32 (d) when outside the 80% limit as per the definition of tr in UG-37, and tr as calculated in the definition (c)of tr when inside it. Unclesyd, is this possibly how your hand calcs were done, & rhg is this what you meant in your post?

BTW, the phrase "and its reinforcment" to me means the limits of reinforcement and not just a pad. Something to watch when putting a nozzle near the edge.

Regards,

Mike

 

[unclesyd]

SnTMan,
I checked today and found out all the archived historical information that was available for a lot vessels has been discarded, even some that are still inservice. The 6 vessels that I referenced have all been replaced inkind and only have a U1 sheet in the files. There are no calculations or any copy of the FEA study in the any of three sets of files that pertain to the installed equipment.

Unfortunately the engineer that made the original calculations is no longer with us.

I made an inquiry to the current AI to see if perchance he has copy of the FEA file folder that contained both the FEA analysis and the original calculations.

 

[SnTMan]

Unclesyd, thanks, let me know if you find anything further.

Mike

 

[rhg]

SnTman:

You are ok: use "tr" in UG-37 as defined in UG-32(d) when calculate a nozzle outside 0,8D

Regards
rhg

 

[SnTMan]

rhg, thanks, Mike