Bracing for nozzle instead of reinforcing pad

[farzam]

Dear All,

we have a in service vessel that regarding our inspection, there are some thickness reduction near a 4"nozzle. A engineering company adviced us using bracing at 4 points of nozzle in order to reduce nozzle loads & moments by attached piping(nozzle has no reinforcing pad). please let me know your idea how this comment could be useful for reduction of loads instead of using reinforcing pad?

Thanks in advance

 

[TGS4]

You'll need to provide more details. Design pressure, thickness, design temperature, etc.

BTW, bracing or other means of support do NOT reduce the nozzle loads, rather they distribute the loads into more material, and (sometimes) lowering the stresses.

 

[JStephen]

Bracing wouldn't reduce the reinforcing requirements for internal pressure. If large external nozzle loads affected the design, it might help.

 

[farzam]

TGS4

OD= 1200mm, DP=1.5barg, DT=130C, measured thickness=5.7mm
please let me know how bracing cause reduction in stress, and if it is so, you do not think, that bracing maybe good solution?

 

[metengr]

farzam;
Your request for assistance is for an experienced pressure vessel design engineer or engineering firm to perform either FEA or calcs, not a forum. There are two issues to deal with; area reinforcement for the corroded vessel itself, and reinforcement of the nozzle wall and sufficient weld size to accommodate moments and tensile/shear loading in service. Seek professional help with this one.

 

[TGS4]

farzam,

After reviewing your original post, I'm with metengr. However, I have never been a fan of bracing/gussets for nozzle reinforcement/stiffening. The likelihood of problems with differential thermal expansion (although probably not an issue with your vessel), vibration, etc, suggest away from using gussets.

As far as the explanation of how gussets reduce the stress, I would suggest that you ask your engineering company - that should be what you're paying them for, isn't it?

 

[prex]

Bracing should be used only where it may be useful to lower nozzle deflections: this might apply to a small nozzle on a thin vessel self supporting a relatively heavy component (e.g. a level transmitter) or where the first support for the pipe cannot be very close (e.g. a large diameter horizontal vessel).
Please check per code all nozzles for reinforcement and external loads without accounting for any brace. If your external loads are individually calculated for your installation (not coming from a general specification), you could instead use the braces as a support for the pipe to determine new external loads (but, to be compliant with code, you should then check vessel wall where the brace is attached!).

prex

http://www.xcalcs.com

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[BillBirch]

I also do not like the idea of bracing. YThere is a tendency by engineering consultants now to detail long instrument nozzles with gusset braces. My concern is that the wels to the pressure parts are difficult to examine and could easily cause local cracking. Also, there is the danger that inferior grade material could be used for the gussets.
Regards,
Bill

 

[LSThill]

Team Members

To be determin by the clint Specification:

Sample is attach Example:
From Paulin Research Group PRG FE-Pipe Version 4111:

Multiple gussets at user specified locations around a center nozzle. The gusset model for center nozzles has been expanded to allow the user to place up to 18 gussets at various locations around the nozzle. (The off-center nozzle model still supports the current 4 or 8 gusset models.


I hope this will help thei above technical question.

Regard
Leonard Stephen Thill

 

[saplanti]

I guess there will be more problem in case the there is a temperature difference between the vessel shell/nozzle and the bracing member.

Ibrahim Demir

 

[kamatr]

One other important element to remember is that gussets impart out-of-plane loads on the vessel shell and in the main, shell structures do not cope well with out-of-plane loads particularly if the loads are of a dynamic nature (arising from agitatators or similar). There are two failure cases that I am aware of where gussets led to through thickness failures at the toes of the welds at the gussets.