ansi 9standards0 code issues - allowable pressure rating

huangyhg

ansi allowable pressure rating
let me first explain the scenario...
currently, we do cavern integrity tests on underground oil storage caverns periodically.  when doing so, nitrogen is purged from the wellhead into a frac tank.  connected to the wellhead is a 2" x 3/4" reducing fitting with internal threads which is immediately connected to a 2" hammer-type coupling and then that is connected to 2" hose into the frac tank.  
my question is...i know that the hammer-type coupling is rated at 2000psi, however, since there is a weak part in the system (the location at which the reducing fitting is threaded to the wellhead), will that location as well be rated at 2000psi?  the overall system must be rated for at least 2000psi.  help please!
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also, i should mention that the following information is all that is printed on the reducing fitting itself...
2" x 3/4"  s/80 a/sa234 wpbn w8297 gt
is there any indication from the above information that may answer my question?
since the threaded part of the reducer is a weak point as you said, i would evaluate the ability for that part to be able to retain the pressure. is the reducer a standard reducer rated for your application? it is rated for your application per the appropirated industry standard (anis, astm, asme), and is it in good shape, it is, then you do not have to worry about it. if not one option is to replace the reducer in question with a standard reducer rated for your application the other option would be to evaluate the reducer. you can compare the minimum wall thichness for youe application with  the wall thickness at the root of the thread. but don't forget there will be stress concentration at where the threads are so you have to factor that into your calculation. you can get a standard text that details how to do this.
good luck!
wpbn w8297 gt may be the heat number. if you have the mill test certificate on the reducer you can verify the chemistry and the design pressure with this information.