WRC 297 - How calculate Mc, Ml, Mt, Vc and Vl

[abbver98]

When analysing nozzle loads according to WRC 297 for example tank with flanged nozzle, values of Mc, Ml, Mt, Vc and Vl are calculated ? There is no method in this bulletin. I can calculate only load genarated by pressure.

 

[TomBarsh]

Bulletins such as WRC-107, -297, and -497 provide a method to determine the stresses in the shell due to the mechanical loads imposed on the attachment. Some of the bulletins address pressure stresses as well, and consider stresses in the nozzle neck also. But the main point is that the bulletins provide a method to determine stresses based on the specified loads, they do not provide a method to determine what the loads should be.

Generally, the loads acting on the nozzle may be specified by a design code or vessel owner's specification. Or they may be unique for the application; in other words, a 12" nozzle on one tank or vessel will have different loads applied to it than a 12" nozzle on a different tank.

ASME Boiler and Pressure Vessel Code, at least in Section VIII, doesn't specify any particular loads to be applied to nozzles. The applications for the end processes are just too varied for there to be one "magic" one-size-fits-all set of nozzle loads.

Now, you could "back in" to a set of allowable loads (forces and moments) for a given nozzle based on limiting the stresses in the nozzle and shell to the allowable stresses. But since there are 3 possible forces and 3 possible moments there will be an infinite number of possible combinations of loads that will all stress the material to the allowable. You can make some assumptions on how the forces/moments might combine and so be able to come up with a practical combination. But if you are a vessel fabricator I don't recommend "volunteering" to find this magic combination unless you are getting pad for each iteration.

Practically speaking, you should consult with whoever is responsible for attaching whatever is going to attach to those nozzles and ask them what loads they expect to have, then use these in the design/analysis of your nozzles.

 

[abbver98]

TomBarsh,
you say design code shall specify the nozzle load. Which code ? (I agree tha ASME VIII doesn't give such information).
I agree with you that tankmaker can't give the nozzle loads because it depends on installation. But he can give allowable loads by fixing some of them (for example he can give Mcmax, Vcmax and fix Ml to aebitrary value). So it's not really very accurate.
I think that the final customer should give the nozzle loads. Do you agree ?
I'm obliged to give the stress calculation on nozzle but only with pressure loads.

 

[TomBarsh]

I believe that some of the API "tank" design code gives some nozzle load requirements. But it's been so long since I've worked with that Code that I couldn't direct you. I suppose that, in general, some other design codes may stipulate minimum nozzle loadings. In the absence of such requirement it is up to the vessel owner to specify what loads they want the nozzles to be designed for.

If you are a fabricator, protect yourself by specifying that the nozzles are not designed for any external mechanical loads.

 

[LSThill]

TomBarsh (Structural)

When will WRC 497 be added to CODEWARE COMPRESS SOFTWARE?

 

[MJCronin]

abbver98,

This discussion may be of help to you..

http://www.eng-tips.com/viewthread.cfm?qid=75687

The problem of allowable nozzle loads needed early in the plant design process is an old one.

There are some professional engineering firms that have established proceedures, keep good records and can develop approximate design loads based on the piping stress analyses done for similar vessels on other projects.

Then, of course, there are the "other" engineering firms (typically loaded with MBAs) who see no value in keeping any kind of records and rotate engineering staff in and out on a regular basis. When there is a obvious need for a code/standard or methodology in the course of the project, the design leader becomes enraged that the newly hired staff engineer does not have it....

ie. "What ???..?? you mean that you don't have WRC 497/297/XXX at home ??..!!??

My opinion only


-MJC