Weld overlay is provided on vessel/ piping flanges for corrosion protection.

In one of the case, weld overlay on flange was considered to avoid galvanic corrosion between dissimilar MOC of vessel and piping flange. In this case, only the face of the flange and ~ 25 mm length (from FOF) on the ID was overlayed to avoid dissimilar MOC contact.

Flanges were first machined on the face and on the ID (overlay surface) to remove the base metal upto ~ 2 mm depth and then overlayed to built up these surfaces and finally machined again to get the smoothe surface.

Removal of base metal is also carried out for RTJ flanges on the flange face in case overlay is required since equipment was also requiring cladding.

Can anyone advise whether removal of base metal from the flange and then built up is allowed as per the codes (ASME sec VIII or B 31.3 or B16.5). If yes which clause of code allow this.

I have seen this practice is followed widely however have a doubt since by removing the base metal we modify the basic dimensions given in B16.5.

Regards
Sanjeev

Sanjeev,
It's not "allowed" in terms of given provisions how to manage it. But it's not prohibited neither. U-2(g) is your friend now

_________________
Konrad Anikiel

Sanjeev,

Konrad is quite right, weld overlay is not prohibited by the Code, therefore it can be considered permitted.

But please note the responsibility aspect: If you use a standard flange, the machining and welding will render it into a NONSTANDARD Flange. Consequently you need to design the flange taking into account the new dimensions, and the weld material. Part UCL and Appendix 2 of VIII-1 are applicable. We have seen many cases where the flange calculation was forgotten.

From the responsibility point of view, the welding organisation becomes the Flange Manufacturer, with all responsibility. The Certification made by the forging shop is no more governing.

DK

Dr Koelbl/ Konrad

Thanks for your replies. I am also of the same opinion that in case of modifying standard flange for the purpose of weld overlay makes it non standard flange and has to be substantiated with calculation.

Unfortunately in my company and the vessel fabricator do not agree with my opinion. Their agrument is that machining is on the flange face and on the inside dia (only in the flange section) and therefore there is no thickness reduction on the hub of the flange and also on the thickness of the flange.

I believe they are also right with their explanation since there is no reduction in the flange thickness and also in hub thickness (metal removal on ID is in above hub section only). Code calculation takes consideration of hub thickness at large and small end only and therefore I am not sure how ID increase is to be considered above the hub section.

Any idea on the same?

Regards

Sanjeev

Sanjeev,
If you want to convince yourself/someone, ask him/yourself two questions:
1. Does the altered flange meet B16.5?
2. Is Appendix 2 applicable to such a flange?

My answer to both is NO.

_________________
Konrad Anikiel

Sanjiv,

if you want to convince, take his/her car as an example.

"Would you still accept responsibility for your car if I take it and machine it over? Not much, only the front and the wheels will be machined. Do not worry, it is still your car, and I wont touch the driver's seat, so you should not be concerned. "

Convincing?

DK

I Know this is a very old topic (3+yrs) but why not just weld on a poison pad ring rather than build up & machine overlay?

Dear Sirs,

I think if you write this issue to ASME, might they will answer the same.

For cladded vessels we also following the same procedure, but we are removing material from flage raised face only & again rebuilt the same with weld deposition. However flane ID will be same as connecting pipe & here the weld deposition is projected inside from flange ID, i.e. if flange ID is 500 mm, then clad ID will be 500 mimus two times weld deposition THK.

_________________
Makrand Pandurang Sakpal,
Static Equipment Design,
makrands9@gmail.com,
Ph no:- 9967949656.