I have a situation here with a bit of a gray area in my opinion. It's been a while since I have really been involved in Pressure Vessel design, etc...

One of my colleagues is performing some in-service pressure vessel calculations based on inspection data on shell, nozzle, head thicknesses, etc.

From ASME VIII, UG45a results in a thickness requirement of 0.0194 for this particular nozzle.....the actual nozzle thickness measurement is 0.2020. So per UG45a, the nozzle is o.k, however, PVElite sites a failure of the nozzle based on UG45(b), (4) (which states that the nozzle shall be at a minimum the thickness of standard schedule pipe,minus mill tolerance, in this case 0.2074 (4" standard schedule minus 12.5% mill tolerance = 0.237in x 87.5% = 0.2074in).

I can understand for a new design that this may make sense to have a minimum thickness as such, however, as soon as a vessel experiences the slightest bit of corrosion in service the nozzle "fails"....this does not make sense to me and does not seem right intuitively.

My first thought on this when he approached me with the question was that there must be a separate requirement for vessels that have been in service...??

Can someone please point me in the right direction here....are there exceptions in this case to the above and if so can you point me in the right direction (i.e. Codes, etc).

Thank you,
Mike

Check API 579 Code, fitness for service. Also refer component analysis part of PV Elite i.e. CodeCalc. But It is not given for nozzle in CodeCalc. Check API 579 properly.

Mukesh