Flange rating 2

[Bmechz]

While checking the flange rating. whether we have to add equivlent pressure due to external loads and moments along with design pressure or not as per Div 1 and Div 2

Baijuz

 

[XL83NL]

So what is your question?

 

[Bmechz]

Equivalent pr.+ design pr. is mandatory or not as per code because some cases it may lead to higher rating flanges.

Baijuz

 

[XL83NL]

Im assuming you're asking whether it's required to check flange rating based on internal pressure + external loads (translated into an equivalent internal pressure)?
So, does one need to take nozzle loads into account by means of the equivalent pressure method for vessels to VIII-1 or VIII-2?
The answer is no.

For ASME VIII Div 1, nozzle loads need to be addressed, but the Code does not explicitly tell you how. The equivalent pressure method is not mandatory in that sense.
For Div 2 I think you can do an FEA analysis, but Im not familiar with VIII-2, so others may need to confirm.

The equivalent pressure method is fairly conservative. To check nozzle loads, a simple WRC107/297/537 check would be better.

 

[SnTMan]

Baijuz, you SHOULD add these loads, per UG-22 (Div 1 only). In practice, it doesn't get done a whole lot. For the reason you mentioned.

Regards,

Mike

 

[TGS4]

I agree with XL83NL - do NOT compare internal pressure + equivalent pressure to the rated pressure for a B16.5 flange. B16.5 itself only cautions the user to avoid severe external loads at high temperatures (Article 2.5.2) - but does not put any limit on what constitutes "severe".

Based on the work in this paper, you could compare equivalent pressure + internal pressure to at least twice the rating pressure for a variety of different sizes and classes.

I also agree with SnTMan that these loads need to be evaluated - unfortunately, there is no methodology provided to do so in Division 1. There is in Division 2, Part 4.

 

[TomBarsh]

"To check nozzle loads, a simple WRC107/297/537 check would be better."

These analyses check stresses in the shell due to the application of the nozzle loads; they do not check that the flange itself is capable of sustaining those loads.

In ASME B&PV Code, UG-22 indicates the loads that the vessel is to be checked for, and if the flange is within the Code boundary then it should be checked for any loads. ASME B&PV Code Section VIII doesn't indicate "how" to address the loads, although Section III (exact paragraph escapes me) provides a method...the old 'Bechtel' formula printed in Moss' book and numerous others. As pointed out above this method may be conservative, and is likely based on gasket criteria rather than the mechanical/structural strength of the flange, but then a flange leaking under nozzle loads is not desirable either.

 

[XL83NL]

Warren Brown actually presented a paper at the last PVP conference in Paris, on this subject. PVP2013-97814: Improved Analysis of External Loads on Flanged Joints
The paper comprises/summarizes a lot of previously work done and presents a new method for determining allowable external loads. It's very decent work presented. Until the paper's up @ asme's website, see here for little background.

 

[XL83NL]

With all due respect, the OP's first and 2nd post were not clear at all. He mentioned 'flange rating', 'external loads moments' and 'Div 1 and div 2', which hinted me to flange connections at the vessel/piping intersection, which is why I assumed he talked nozzle loads. When reviewing, I now understand he may tried to explain something else.

Again, the paper presented by Brown also discusses the external load method discussed in ASME III.

 

[TGS4]

XL83NL - good reference. Dr. Brown's paper is very informative (I should have reached for that one, too - I substitute-chaired the session in which that paper was presented...).

The methodology Dr. Brown applies is new, but straight-forward, incorporating elastic-interaction between the flange and the gasket. Based on his results, there is definitely extra external-load-carrying capacity in most standard flanges.

Summary - DO NOT compare internal pressure PLUS equivalent pressure to the rating pressure ONLY. That is excessively conservative.

 

[Bmechz]

Thanks for all the above informations.

Now iam facing problem in div 2 vessel. our client commented that as per Asme sec viii div 2 clause 4.16 .2.2,MAWP of flanges shall be computed considering also the external loads.

My interpetation of the above clause is that it is to be used only for non standard body flanges.

So i request you guys to write me your point of view regarding the above comment

Baijuz

 

[TGS4]

4.16.2.2 is for ALL flanges. However, there is a methodology in 4.16 to handle external loads. Use it - it is mandatory.

 

[Bmechz]

Hii TGS4,

First of all i thank you for your valuable reply.

According to understanding this cl. 4.16 is same as appendix 2 of Div 1 and is applicable only for non standard flanges. Kindly correct me if iam wrong.

If this clause is mandatory for all bolted flanges then rating will go very high and will increase the cost of fabrication, as you know almost all specification is having very high nozzle local loads(due to piping and other nozzle loadings).

Baijuz...


Baijuz

 

[SnTMan]

Baijuz, calculate the required flange class per your client's requirements. Inform the client all his mating flanges will need to be changed to this rating. See if the client then grants some relief. They often back off when their own specifications affect their plans.

Regards,

Mike

 

[TGS4]

4.16 is similar to, but not identical to, Appendix 2 in VIII-1. The difference primarily is in the provision for how to deal with external loads. Don't assume that you will have a problem - run the calculations yourself and then make conclusions.

And I completely agree with SnTMan, these very high loads are not your problem, but your client's problem. Identify to them the cost of implementing their specifications. Sometimes a good slap up-side the head of reality if enough to straighten them out.

 

[Spoonful]

Perhaps you should check for flange leakage and stress, with given external load. And by doing flange analysis you will probably find that most Class 150 flange will fail even without any external load.

 

[TGS4]

Spoonful - perhaps you should read the entire thread - that's exactly what we're talking about. Only the methods that you are referring to are not exactly modern and there are much newer methods available (again, read the thread - these new methods are what we're talking about).

No - most Class 150 flanges (except the four-bolt ones and the NPS 8) are fine for their internal pressure and some additional external loads, depending on the initial assembly bolt stress.