Old ASME "U" stamped vessel nozzles don't meet Code

[cmsurfsup]

I am working on ASME B&PV Section VIII, Div. 1 calcs for an existing ASME "U" stamped vessel at my facility. The problem is that while the vessel nozzles meet the minimum thickness requirements per UG-27, they do not meet the thickness requirements of UG-45. The nozzles range from 1" to 3" Schedule 5 pipe. The vessel was built in 1991 to the 1986 edition of the Code. I couldn't find the 1986 edition of the Code to see if the UG-45 requirement existed. But the 1989 edition did have it.

My question is how could this vessel be Code stamped if it did not meet UG-45? Does anyone any suggestions how I can keep using this as a Code vessel without derating it? Would ASME Code allow a finite element analysis instead?

Thanks!

 

[metengr]

First, what are you exactly doing with this in-service pressure vessel? Are you performing a fitness for service, alteration (re-rating) or what?

 

[cmsurfsup]

At my government facility, we are required to recertify pressure vessels every 20 years. Recertification involves verifying the vessel meets all the current ASME and local pressure vessel requirements. As part of that recertification effort, the ASME B&PV Code calcs are redone. When the vessel was first certified in 1991 by a subcontractor, they did not perform the UG-45 calculation.

There have been no indications that there is anything wrong with the vessel. This is merely an exercise to verify that the vessel meets the current requirements and has not exceeded it's remaining pressure /temperature cycles.

The vessel is a LN2 dewar with a MAWP 0f 53 psi.

 

[metengr]

What you are performing is a fitness for service. If the nozzles were supplied as standard fittings with integral reinforcement, this could have resulted in not requiring UG-45.

 

[Ready2go]

cmsurfsup, would it be that a corrosion allowance wasn't originally considered and you are putting this in to your calculations
In some circumstances especially low pressure vessels, the rules governing nozzle thickness in UG-45 can be avoided
Just a thought....!!!!