I need to check influence of external loads (comming from pipe lines connected to pressure vessel) on nozzle flanges. Does the Code say anything about it, what is your opinion?

Thanks,
Malyl

The code says you have to take into consideration/calculation such loads. But doesn't say how to calculate it. This means you are free to choose the method. I use FEA and it works pretty well.

_________________
Konrad Anikiel

Hello Malyl,

A common way is to use an "equivalent" flange pressure when you have to consider external loadings. This means you increase your design pressure by an additional pressure due to this loadings. The formula to determine the equivalent pressure is:
Pe = ( 16 M/ Pi G³) + ( 4 F / Pi G²) + P
M is your resulting moment and F the axial force acting ofn the flange. This formula is taken from the "Pressure Vessel Design Manual" of Dennis R. Moss, however, you can find it in many engineering handbooks under "good engineering practice".
I have a small Excel spreadsheet attached with this little formula, maybe it helps: equivalent-flange-pressure.xls. Please check if it fits to your problem and works correctly before use
Best regards
Michael

Hello Michael!
Thank you for your support. I already knew that formula, but the problem is that when I use it, I go far beyond flange ratings. That's why I was trying to find in the Code exact requirement for such considaration of external loads in flange calculation. I need to convince my client "no code requirements - no checking"

Best regards,
Malyl.

As you know for sure, in UG-22 (c) you will just find that such loads have to be considered. However, the way how you will find in U-2(g), e.g. with this simple formula. I agree with you that the additional pressure often kicks the flange out of the rating table of B16.5.

The experience I have made is the following: When the client learns that he needs class 300 flanges instead of 150, the load location moves from the end of the nozzle to the nozzle-vessel surface intersection (and the flange is free from loads).

However, there is only one possible procedure. The client has to determine the location of the external loads. You have to follow the code and your solution "no code requirements - no checking" will cause following problem: There are code requirements!

Best regards
Michael

The question is, how can we convince the client that flanged connection is completly rigid without influence of these external loads and that we can move them (the loads) directly to nozzle-shell surface intersection and preform only WRCB or similar calculation?

Best regards,
Malyl.

In my opinion: you can´t. When the client detemines acc. to UG-22 the loadings which have to be considered, and external loads acting on the flanges are one of them, you have to consider them.
On the other hand such loadings often come from general specifications which are theoretical and far away from reality. If you are able to convince the client that his specification is not applicable in your specific design, you have solved your problem. However, it´s difficult to find someone who will take the responsibility for changing the spec´s, even when it´s clear they are nonsense.
Best regards
Michael
Besides: Are the flanges within the scope of the ASME Code, or do they belong to piping?

The problem is both for pressure vessel's nozzle flanges and also for flange connections on our pipelines. Loads even they are calulated by piping department are still theoretical and as you wrote "nonsense" E.g. looking at the piplines and vessels done 20 years ago, which are still working fine and they were never checked for such stresses, but now when you use "new approach" methods they are overstressed!
Maybe, for the moment, the only solution is to check flanges using FEA and try to minimize loads?

Best regards,
Malyl.

I am late to the table for this topic! But perhaps my comments may help others.

Some designers or vessel operators may question the validity of applying external loads to the flange design, claiming that vessels have successfully operated for years. It is fundamentally clear that any structural loads are passed through a connection and the nozzle flange is a structural connection. Determining the true loads applied to the shell through the flange is very difficult and the specified loads may not reflect the true loads. ...This is as others have mentioned (ie: calculated loads for specific application versus loads that come off a standard contract document).

Vessel owners may question "Why haven't the flanges failed in service?". Some responses are: The true loads may be much less than the calculated loads. Similarly, ASME/ANSI flanges may have structural strength beyond that given by their pressure-temperature rating.

At best, overstressed flanges may be prone to requiring frequent maintenance due to leakage, etc. At worst, an overstressed flange may fail during service.