Is Long Weldneck Flange Considered as a Standard Flange?

You wrote:

"can we consider long weld neck flange as a standard flange irrespective of neck length."

The answer to this question is: Sort of. The outside diameter, the bolt circle diameter, the number of bolts, the size of the bolts, the gasket contact area, etc. of the long weld-neck (LWN) flange is the same as the normal "Weld-Neck flange. The only difference between the two is the physical geometry of the neck portion. The will mate together just fine. The normal use for the "LWN" is for making nozzles for vessels and exchangers.

Look here for details and dimensions for "Long Weld-Neck" flanges

http://www.texasflange.com/Long%20Weld%20Necks/Long%20Weld%20Necks%20Standard%20Connection.html

Your next question was: "Can we consider it as a Standard flange?". By this I assume you are asking if you can weld it to ordinary pipe in place of a normal Weld-neck flange. Well yes and no.

Yes you could do it ---

but

No, not without a lot of costly modification to the end of the LWN to insure that the O.D. of the LWN matches the O.D. of the Pipe and then make sure the I.D. of the LWN matches the I.D. of the Pipe. Then you must grind the correct weld bevel so you can make a proper weld.

Thank you PennPiper,

This is regarding multilayered vessel design, could you please give me an idea or reference text of how to design multilayered high pressure vessels apart from that given in codes. I have been searching it for quite some time now but, have no success yet, kindly help.

thanks again