Level A-D, Nozzle Loads Checks 1

[knandwana]

Hi,

I am having huge trouble meeting the customer requirement on a 4" Nozzle. The loads are as follows :

P(lbf) V(lbf) Mt(ft*lbf) Mc(ft*lbf)
185 210 885 276 Weight
278 315 975 414 Seismic
467 575 1355 736 Thermal
930 1100 3215 1426 Total (W+T+S)

Now, if I apply the Total Load on the 4" Nozzle, the stresses are very high, way more than the allowable Stress, (P.m+P.l) 1.5Sm and (Pm+Pl+Q) 3Sm.

Now, am I missing something. Do the allowable stresses change in case of seismic and thermal loads?

What is meant by different Level A,B,C,D ?

This is the first time I am doing Nozzle loads.

Any pointer will he helpful, since I am on a very tight schedule.

Thanks,
Kapil, EWI

 

[TGS4]

This question was essentially asked and answered in thread794-264729.

It would appear that you are in need of some mentorship. Is there not anyone at your company that you can turn to?

 

[vpl]

knandwana

The meaning of Levels A, B, C, and D are defined in the ASME Code and refer to different operating conditions from normal to upset.

You really need to get a copy of the Code and familiarize yourself with it. It sounds like your customer expects a vessel that meets Code. It also sounds like you have a nozzle that isn't meeting Code. That, to me, means you need to redesign your nozzle using the Code. Which leads back to getting a copy and becoming familiar with it.

And before you ask, you'll need to buy a copy.

Patricia Lougheed

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[MrBTU]

Basically your options are to beef up the nozzle neck, the shell, both, or add a reinforcing pad until you satisfy the load requirements. Sometimes I tell the customer (or sales) that "our normal design" (for design press and temp alone)with be able to handle X forces and moments, and to accomodate your additional loads we need to do the following x,y,z, which will result in a price increase of $, and sometimes a compromise ensues, or sometimes not. But, if you have taken the order based on press and temp only, you need to alert the customer that these additional loads will add some cost. Good luck!

 

[Mandeep1]

Kapil,

In your analysis are you classifying the weight loads as sustained, thermal loads as thermal Expansion (resulting in secondary stresses) and seismic loads in occasional categories.

Then, you can take advantage of the limits from Div.2 for various stress combinations.

btw, the limit for Pm+Pl+Q is 3*Savg, where Savg is the average of the allowable stresses from the ambient condition to the operating condition.

MrBTU has good suggestion. If the loads are excessive then piping may not have been designed properly.

It may help a little if they account for the flexibility of nozzle in their piping model.

Good luck.

best regards,
Mandeep Singh

 

[jte]

Mandeep-

Care to provide the paragraph number in Div. 2 which discusses Savg?

Thanks.

Kapil - Piping loads "including those attributable to restrained free end displacements of attached piping" can result in primary stress. As TGS4 mentioned above, just because a load on a nozzle is created by a thermal expansion effect (external to the vessel) does not make it a secondary stress. Read the code for yourself, and make your own decisions. The advice you get on this or any other internet source is worth pretty much what you paid for it. You're the engineer, its your responsibility. In Div. 2 2009, look at 5.6 on page 5-29 and Table 5.6 on page 5-46. You need to consider whether you are within the limits or reinforcement or not.


jt

 

[Mandeep1]

jt,

Yes, I should have provided the section of the code,

The Savg is actually SPS now. Which in some cases be higher. Refer to section 5.5.6.1.d of ASME Sec. VIII Div. 2 2007 Ed 09 Addenda, which defines SPS and shows that you have take average of the vales from the highest and lowest temperatures during the operational cycles.


The section 5.6 in the Div. 2 2007 Ed. 09 Add., refers to the stress classification for the nozzle neck. This agrees with what you wrote.

But, for the classification of the stresses in the Shell at the nozzle junction you are referred back to section 5.2.2.2, which states that Pm (general Primary Membrane Stress) include "design internal pressure and other specified mechanical loads but excluding all secondary and peak stresses".

So, if you are checking stresses in the Shell at the nozzle junction the thermal expansion loads should be classified as Secondary.

Further, the Table 5.6 clearly states this as well.

Now, for nozzle neck the classification Div. 2 code has classified the thermal loads as Pm.

WRC-107 is computing the stresses in the shell only and not nozzle neck.


best regards,
Mandeep Singh

 

[TGS4]

Mandeep - your interpretation of 5.2.2.2 and Table 5.6 is incorrect. stresses from loads caused by free thermal expansion are not classified as secondary, but fall under the "specified mechanical loads" which cause primary stress.

For reference, see the papers that I point to in thread794-264729.

 

[vpl]

Out of curiousity, do we really know that Section VIII applies? It could be Section III. Knandwana never stated what code he was using and my impression was that he didn't have a copy.

Patricia Lougheed

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