App 2 flange vs standard flange 1

[vessexst]

Hello,

I have a question regarding the use of appendix 2 flanges vs standard flanges

If the diameter of heat exchanger is such that standard flange of ASME B16.47, series A can be used, should you go for a standard body flange or a non standard flange??

Since, I have noticed that a standard ASME flange, if calculated as per the rules of appendix 2 fails.
Moreover, standard B16.47 Series A flange, if checked as per rules of appendix 2, require a higher thickness than a standard B16.47 series B flange

 

[DriveMeNuts]

Have a look at UG-44(i).

 

[GandalfTheGrey]

Standard flanges should be used wherever possible. The cost of designing and fabricating a custom flange is expensive and should be a last resort. If a custom flange is required, and there is no alternative, then the procedures included in Mandatory Appendix 2 can be utilized for designing a custom flange. The ASME Code accepts the standard pressure-temperature ratings of ASME B16.5 for flanges, classes 150 to 2500, ½” to 24”. For larger diameter flanges use ASME B16.47.

 

[vessexst]

Thank you all for your comments. It was helpful
But why do the standard flanges fail when the same parameters are designed as per appendix 2?

 

[SnTMan]

Any halfway reputable HX manufacturer will provide custom designed girth flanges as a matter of course. The advantages of doing so are too many to list. If your fabricator is offering a B16.47 girth flange, find a different fabricator. If you are the fabricator, hire a designer that knows what he's doing.

Standard flanges often fail under Appendix 2 because the design rationales are not the same.

Regards,

Mike

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

 

[vessexst]

@Sntman: So, do you mean to say that the use of standard body flange for a heat exchanger is not a recommended practice? BTW, I have heard of a U stamp heat exchanger using a standard body flange and passed by AI. Dont know if it is true or not but I did hear this

 

[SnTMan]

vessexst, absolutely, std B16.5 / B16.47 flanges may be used as body flanges, and it may make a certain amount of sense for some pipe sized units. But you have so much more flexibility with custom-designed flanges. The exact inside diameter desired, widest possible choice of styles and sizes of gaskets, male / female raised faces as needed for confined joints, explicit design consideration of pass partition ribs, explicit consideration of any client special design requirements and so on.

And really a Series B flange would typically be preferred over a Series A anyway as it is a more compact flange. Few shell & tube fabricators would ever consider something like a B16.47 for a body flange.

Regards,

Mike

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

 

[r6155]

IF owner and manufacturer agree then ASME B16.47 is OK.

Regards

 

[Michael B]

UHX-4(b)says that if pass partitions are present, then standard flanges are no longer standard; hence you have to design per Appendix 2. Or account for them in some other manner.