Checking of ASME B 16.5 Standard Nozzle flange with External loads to ASME Sec VIII Div APP-2

[DK44]

Dears.
Our client asks us to Check Standard Nozzle Flange with external loads independently to ASME Sec VIII Div App-2. When we check the design by PV Elite for the Flange to APP-2, it calculates Peq from FA and MC and ML (Peq = Design Pressure + (4*FA/PI.G^2) + (16 ME/ Pi. G^3) where ME = (Mc^2 + Ml^2)^0.5) and uses in H Calculation only. Such calculations pass even though Rating Pressure (PR) is much less than Equivalent Design Pressure Peq and even it fails in derating to UG-44.

Now the questions are:
1. Why PV Elite does not use Peq in Hp and Hd calculations?
2. Is such verification acceptable to code under U2-g?

 

[DK44]

May I have the learned response to my query.

 

[SnTMan]

DK44, I am trying to understand your post. I get that your client wants you to check standard nozzle flanges for external loads by Apx 2. The eqn you cited appears to be a standard formulation existing for many years.

This would seem straightforward: Knowing the required values, calculate Pe and use it wherever P appears in the Apx 2 calculations. No idea why PVE would use it in H only, you'd have to ask them. Looks wrong to me.

A complication is that B16.5 flanges often enough do not pass per Apx 2 calculations. You might check this absent the external loads.

Not sure what is meant by your statement "Such calculations pass even though Rating Pressure (PR) is much less than Equivalent Design Pressure Peq..." You are saying that Pe is above the flange rating pressure, and that the flange also meets Apx 2 at that Pe? If that is the case I don't see how that flange could be considered sufficient.

I'm not familiar with current Code, but if, as I understand, UG-44 incorporates a method to check for external loads, you'd be bound by it. You could of course perform the client calculation alongside this, but you'd have to meet the former and not necessarily the latter.

If the clients' selected flange ratings will not meet his supplied nozzle loads, he will need to make some decisions.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[DK44]

SnTMan (Mechanical). Thank you for your elaboration which is in line of my thinking also.

1. May I request the PV Elite experts and others to clarify the point why Pe is not used by the program for calculating Hp and HD also.
2. Because of this discrepancy, the flange passes APP-2 calculations with Pe, even though it Fails in rating pressure vs Pe & Derating Calculations to UG-44 of Div 1.

 

[Some Curious Guy]

You should get your hands on the ASME Paper PVP 2013-97814 that led to Code case 2901 or UG-44(b). The following is an excerpt of the paper.

I am not an expert PVLite user but I guess PVlite is using a combination of equivalent force and equivalent pressure method. It is applying Peq only to H so the effects of external forces and moments are not considered twice.
The current version of the code does not mandates the use of UG-44(b)/Code case 2901. You also have to meet the assumption written in UG-44(b) and notes of table UG-44-1. So your client is within its rights to ask you to evaluate loads using an alternate U-2(g) method. However why would you want to use an alternate method and rack your brain in ensuring its relevance when you already have an ASME recommended method available.

 

[DK44]

Some Curious Guy (Mechanical) Thank you for the reference.
The problem is that the standard flange selected by rating well passes Design pressure of the Exchanger where as, it fails the Derating to UG44(b)considering external piping loads. To justify the rating selection with external piping loads, in view of connecting Piping Flange, Client wants to check for Pe conditions. If we stop with UG44(b) evaluation, the rating is not suitable which affects the mating Piping Flange which the Client probably do not want to change. In these circumstances, to resolve the issue, is that the client to review the nozzle loads and reduce to the extent they pass all calculations? After all the Heat Exchanger is not an anchor point for Piping always.

Yes it is really brain racking due to attempting to pull the code to every body's benefit.

On the double effect, I observe that even with the design pressure PD, it is applied for H and also for gasket sealing via m factor. Hence if Pe is to replace PD is it not be considered in same way every where in place of PD.

 

[Some Curious Guy]

Thanks for the clarification.
In general, UG-44(b) method is less conservative than equivalent pressure , equivalent force and Div 2 method. If the standard flange fails with UG-44(b) method it would probably fail with other methods too. There could be some exception but this an general observation.

Per my opinion the most favorable path forward is to revisit piping analysis and reduce loads till it falls within acceptable limits. If nothing works then increase the flange rating of both vessel and piping flange.

In the past people would find loopholes in the code language and tried to magically vanish the loads away from the flange. This does not work anymore. So do not follow this path. Just saying this because I have seen people follow this path and later face hurdles in Code Stamping.

 

[DK44]

Some Curious Guy (Mechanical)
Agree with your views fully.
1. Is it technically acceptable that usage of Pe (as explained) in H calculations only and not in Hp and HD calculations?
2. Can an Authorised Inspector accept such calculations?
3. Of course Standard Nozzle Flange Design to APP-2 may fall outside the jurisdiction of Code.

 

[Some Curious Guy]

@DK44
1. Yes equivalent force method is an popular method and is technically acceptable. PVLite is a very reputed software and it won't suggest a non technically acceptable method to its users. You can gather more background on this method if you email the PVLite support team.
2. I am not an Authorized Inspector so cannot answer this one. However there is an anomaly in the results you are getting. Generally if a standard flange fails in UG-44(b) it will also fail in equivalent force and equivalent pressure method. Are you considering the direction of forces and moments properly in your input? Are the effects of external force and moments cancelling each other. Please check this ? Perhaps your AI would ask you to validate the flanges using another method just to remove any doubts. Have you checked the flange using Koves method adopted in Sec VIII Div 2.
3. Generally the word "recommended" in the code is read as " recommended but not prohibited if proper engineering judgement is used ". Hence it falls under U-2(g).

 

[DK44]

Some Curious Guy (Mechanical). Thank you once again.
Yes I fully agree on PV Elite reputation and reliability, which is most widely used and accepted by Pressure Vessel Engineers world wide. Accordingly there could be valid reasons for such considerations in this instance, may be in line with that opined by you previously.