Posthydro welding 1

[JackWayne]

We have an ASME Code Vessel that has been completed through hydrotesting. The question has now been asked if we can move the nameplate bracket to a new location. My understanding has always been that if we weld on it again we will have to rehydro it. I have seen an answer in another thread that if the welding is for an external attachment (IE; Nameplate bracket) we don't have to rehydro it. Is this correct? Where in the Code does it specify this?

 

[metengr]

The answer is no for Section VIII, Div 1. If you read UG-99 (a) 1, it seems clear to me that the hydrotest is final. Attaching a nameplate by welding is part of final fabrication (in my opinion).

Put yourself in the position of the AI. Let’s suppose we decide to fillet weld brackets to a pressure vessel and let’s suppose something went wrong and introduced a crack. Now you have a potential problem with a new vessel. I agree, the above scenario is remote if proper weld practices are followed. Codes are conservative.

If this were a boiler, Section I does permit some flexibility for post hydro weld repairs to P-No 1 base materials. However, it is up to the AI for these types of weld repairs as final acceptance.

 

[vesselfab]

you can do a "standard repair" with R-1 form.

Not in code under NBIC repairs.

 

[racookpe1978]

Attaching a Pressure Vessel/Boiler nameplate is usualy no more than a couple of tack welds on the exterior shell of a thick-walled vessel, affecting no more than few 1/4 inch areas. Adds less than what can be felt by hand to even the nameplate, much less the tank itself.

Yes, it is "welding", but why would you consider that enough heat to material affect metal properties?

 

[metengr]

racookpe1978;

Yes, it is "welding", but why would you consider that enough heat to material affect metal properties?

It makes no difference what you or I think regarding the above. It is a Code requirement regarding no fabrication welding after hydrotesting.

If you need to re-attach the nameplate do it after the vessel is commissioned under the NBIC.

 

[stanweld]

racookpe1978
Unfortunately, very small welds can easily create cracks in the pressure part HAZ depending on chemistry and cooling rate and weld filler metal selection. Will they grow under the loading conditions - maybe not, maybe so.

 

[JackWayne]

Thank you all for your responses, I thought the answer was that we would have to rehydro. The vessel isn't in service yet so if they really want to move the NP bracket we will just rehydro and time it for the A.I.'s next visit.

 

[jte]

Wouldn't be the first time a vessel had an R stamp before being put into service. Attaching a nameplate bracket can be a very minor exercise. Under NBIC would I be *required* to hydrotest a repair such as adding a nozzle with no calc's? Or is the hydrotest left to the AI's discretion?

Often a nameplate would be placed near a manway. Often manways have structural connections near them such as manway davits or platform clips. Welding to these should not be an issue if such a location would be acceptable.

jt

 

[metengr]

jte;

Under NBIC would I be *required* to hydrotest a repair such as adding a nozzle with no calc's?

No.

Or is the hydrotest left to the AI's discretion?

The rules for alternative exmination and laternative testing methods are very clear - NDT or pressure test.

 

[SNORGY]

With a view towards getting around issues such as these, I once was called to the field where they used rivets instead of welds to affix the nameplate to a plate heat exchanger.

They simply rivetted it to the plate pack.

They avoided the welding, and avoided redoing the hydrostatic test, but for some reason, it still leaked.

How I wish this wasn't a true story.

Regards,

SNORGY.