Grinding after hydro

[DCMV]

We are building a new pressure vessel per ASME Sect VIII Div 1. We have completed the vessel and pressure tested the vessel with AI present and stamped. Now we noticed the Client drawings call for the internal welds ground flush. Do we have to re-hydro the vessel if we just grind the welds smooth and flush?

 

[Ripz]

This is the applicable passage in ASME Section VII Div 1. It all depends on your interpretation of the code, as it does not clearly state whether it considers grinding welds flush as cosmetic or not.

I consider it as part of fabrication as it would affect your weld reinforcement, and it could have been done prior to testing thus hydrotesting has to be redone.


UG-99 STANDARD HYDROSTATIC TEST
(a) A hydrostatic test shall be conducted on all vessels
after:
(1) all fabrication has been completed, except for
operations which could not be performed prior to the test
such as weld end preparation [see U-1(e)(1)(a)], cosmetic
grinding on the base material which does not affect the
required thickness;

 

[metengr]

No, you do not need to re-hydrotest.

 

[Ripz]

Why not?

 

[metengr]

cosmetic
grinding on the base material which does not affect the
required thickness;

The above is self explanatory.

 

[Ripz]

Like i said, unless ASME says something definitive regarding this issue, it'll always be up to your interpretation. They speak about cosmetic grinding on the base metal; so it all depends on if you consider it cosmetic. Also, they address base metal and not the welds.

 

[DCMV]

That's my question what is considered weld end preparation? The drawing that where revised after call for welds to be flush and edges rounded to 6mm.

 

[metengr]

Flat topping welds is not that uncommon, and I have seen it done after fabrication and hydrotest with no subsequent hydrotest because the vessel is considered completed. After re-reading your post, if the vessel is indeed completed ASME code ends when vessel fabrication is completed, hydrostatically tested and stamped. This is no different than if welding were to be performed on a completed vessel, in this case the NBIC would be invoked not ASME Code.

 

[SnTMan]

VanChe, sounds as though you are talking about nozzle openings? I'd say Code does not require it, but your AI or client might. BTW a weld-end usually refers to a nozzle that will have piping field-attached by a butt-weld.

Regards,

Mike

 

[DekDee]

I agree with metengr regarding not having to be hydrotested again.
However, I would like to put a bit of a different slant on it by way of a query.
Would you have to perform MT or PT again if it was originally required ?
IMHO, yes it would have to be retested.
A volumetric discontinuity may be acceptable if it is sub surface but if the reinforcement is ground off and the same discontinuity is exposed to the surface it may be not acceptable.
Also, internal defects (elongated cavities, slag, porosity etc) that could not be detected on the initial test may very well be surface breaking defects after grinding off the reinforcement.
Your thoughts ?
Cheers,
DD

 

[dineshakabari]

I agree with RipZ who stated "It all depends on your interpretation of the code, as it does not clearly state whether it considers grinding welds flush as cosmetic or not." As per opinion, how you convince this to AI. So it's solely based on the judgment/policy of AI if grinding is not affecting to the required thickness of vessel.

 

[DCMV]

The vessel will be rubber lined, having said that the hydro test has to be complete prior to the application of the lining. The tuber lining procedure has surface prep requirements of rounding nozzle openings to 6mm and smoothing out weld reinforcement.