Removing Code "pedigree" on shell side of Heat Exchanger

[Bocephus50]

Large condensor (horizontal tubular ht xchgr) has over 1400 3/4 OD tubes which contain cooling water at 30 psi. The shell surrounding the tube bundle contains a gas/vapor at less than 5 psi. Both the shell side and tube side are rated at 50 psi and Code (U) stamped.

The shell has developed 2 very serious cracks (180 deg. apart) in the middle shell course propogating from large inlet nozzle in top of shell. Due to the large cracks, best NBIC repair method would be to replace the shell course and inlet nozzle, however the shell portion does operate at less than 5 psi.

Jurisdictional rules require vessels greater than 15 psi and 5 cubic feet be Code stamped...since shell side operates at less than 5 psi, could new saftey valve(s) set at 6 or 7 psi be installed on shell side and the Code stamping for the shell side be obliterated on the nameplate? Then the repair of the cracked shell could be done as "non-code" till new vessel can be received and installed? (Typically, the shell side is operating at about 1 to 2 psi). The Code pedigree for the tube side and channel side would remain since they do exceed 15 psi.

 

[gr2vessels]

Bocephus,
I believe there was a good reason for designing both sides for 50 psi, because in case of failure, the shell side could see 30+ psi. My advice is to not rubbish the good condenser with cheap spin to the code and do the right thing, do the repair as per the code and you will sleep better at night, without keeping vigil waiting for the knock on your door. Murphy says if it could go wron, it will.
Cheers,
gr2vessels

 

[Guest102023]

I concur with gr2vessels, do the right thing. How much more can it cost anyway?

At the same time you should have a metallurgical F/A done on the cracks. A good failure analyst will include recommendations for reducing the risk of recurrence.

 

[unclesyd]

I concur with the post above and strongly recommend that the reason for cracking be determined prior to repairs so appropriate measures can be taken to eliminate future cracks. if the vessel is replaced in kind you will still have the cracking potential seen on the presently installed one. At the same time check the piping around the nozzle as vibration and loading are some causes for cracking around nozzles.
In my career (40+ years) I've seen one nameplate removed from operating equipment.

Could you post a picture of the vessel and cracked area?

 

[Vinch]

I concur with the above posts. Moreover, I think lowering the MAWP on a pressure vessel is seen as a Alteration in most jurisdiction. So you have to deal with them anyway.

 

[blacksmith37]

The Code Stamp applies the day the new vessel is released for service. From then on it is the responsibility of the owner to operate and repair the vessel prudently (according to state law, etc).

 

[Bocephus50]

Metallurgical testing is being done to determine cause of the cracking and condition of the rest of the vessel, new condensor on order.