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Welding Thermowells to U-Stamped Pressure Vessel
2

Welding Thermowells to U-Stamped Pressure Vessel

Welding Thermowells to U-Stamped Pressure Vessel

(OP)
We have a new U-Stamped pressure vessel in our facility.  Due to service requirements, it was PWHT.

For several reasons, the vessel arrived without the thermowells welded to the vessel (although the coupling for the thermowell was welded).

We are trying to decide the fastest and most cost effective way to weld the thermowells to the vessel and still meet B&PV code.  The concerns, amoung others, is the affect of the new weld on PWHT, the need to hydrotest after the weld, and NDE requirements.

Suggestions would be appreciated.

RE: Welding Thermowells to U-Stamped Pressure Vessel

Sir,

Did you look @ API-510?

There is a way around hydro testing with doing more NDT's.

Cheers,
Faraz
 

RE: Welding Thermowells to U-Stamped Pressure Vessel

Assuming that the vessel is registered with the National Board, repairs are required to the NBIC. Provisions are defined therein regarding NDE in lieu of hydrotest. You will need to contact the Owner and/or its Engineer whether you may use the Alternatives to PWHT defined in the NBIC.

RE: Welding Thermowells to U-Stamped Pressure Vessel

If the coupling for the thermowell is threaded, why not use a threaded thermowell?  If welding is required, "repair" the vessel to NBIC and locally PWHT.

RE: Welding Thermowells to U-Stamped Pressure Vessel

(OP)
The coupling is welded.

Based on U-1(e)(1)(a), the opinion was expressed that this thermowell is not included in the code.  Thoughts on this please.

RE: Welding Thermowells to U-Stamped Pressure Vessel

I would concur that the thermowell is excluded from the scope of the code as per the clause noted.

Refer to interpretation VIII-1-89-115, which is quoted here: thread292-262542: Welding pipe to pressure vessel nozzle. (Sorry no link as eng-tips is blocked in the country I'm in, and am using a proxy server)

RE: Welding Thermowells to U-Stamped Pressure Vessel

It would seem that what's being argued in the code case is that welding to a NOZZLE of a vessel does not affect the registration of the vessel itself.  However, any welding to the shell or heads etc. would be considered a "repair" and require an R stamp etc.

Any welding would be subject to the applicable code.  In the case of welding pipe to a pipe stub nozzle, a piping code would apply rather than the vessel code.  You'd need to either hydrotest or pneumatic test, or do the special NDE/sensitive leak test etc. to avoid a hydrotest per that piping code.  

But what code would apply to welding a thermowell into a (presumably) socket welding or threaded coupling?  Is that a matter for the owner to decide?

What if the thermowell is to be full pen welded into the shell or head?  Surely in that case, both the thermowell and the full pen weld are subject to the requirements of the vessel code?!

RE: Welding Thermowells to U-Stamped Pressure Vessel

U-1(e)(1)(a) is not applicable here because the thermowell is not a piping. U-1(e)(4) is more suitable in this case. Please review Code Interpretation VIII-78-97. It dealt with seal welding of threaded piping fitting. The interpretation consided this welding outside scope of the code.
 

RE: Welding Thermowells to U-Stamped Pressure Vessel

If the vessel has been stamped, hydrotested and is completed as in a master data report, this vessel is completed and is no longer under ASME B&PV Code in terms of fabrication.

Any welding to the vessel mentioned above is either under API 510 or the NBIC (National Board Inspection Code) and Jurisdiction rules, if applicable, will be followed.  A re-hydrotest is not required for this activity, and would serve no useful purpose. NDT would be required.

Most likely, the designer of the vessel needs to be contacted to determine if local PWHT or an alternative PWHT method can be accepted. There is not enough information regarding process application and service conditions to provide an opinion.

 

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