Root Weld of Super Duplex

[iam42]

Hi Guys,

I have just completed a Super Duplex PQR and there is a 2" long area where there is some heat tinting. The rest of the root look great.

This test coupon has to undergo G48 Method A corrosion testing. Would there be any advantage or disadvantage to grinding the root flush as this is what will actually happen with the production weld?

Thanks

 

[EdStainless]

A G48A? At what temp?
I am surprised that it isn't a method C.
But even more I am surprised that it isn't a A923 test.

The production parts will all be ground flush?
If so then I don't see the harm.
What will be done after grinding in production?
Unless you pickle afterwards it will likely lower the pitting resistance.
When you grind you just embed the oxide into the surface.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

EdS is right, heat tint must involve grinding followed by pickling.
A good duplex SS tech spec will specify minimum purge gas purity.
Google "IMOA" "Practical Guidelines for Fabrication of Duplex Stainless Steels"

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[iam42]

Hi guys,

The G48 is being carried out at 40C per customer requirements.

Ironic, we used a pretty good oxygen monitor from Huntington Fusion and I was able to maintain the oxygen level at 30 to 40 ppm. The weld was 24” long and was like the inside of a wedding ring with no heat tint whatsoever except for the 2” I mentioned which was right in the middle of the weld length. I am at a loss why this occurred!!!

Thanks.

 

You're using a good instrument.
Even on a bench it is very difficult on an open root pipe weld to maintain high purity in the backing gas. Your welder needs to be very skilled in all the necessary techniques and tricks.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[matschka]

I suggest you use a carbide rotary burr of the highest quality instead of grinding SS,inconel,CU/NI or duplex to remove any hint tint and to make any cosmetic repairs. As EdStainless has said 'when you grind you just embed the oxides into the surface'. This is why I always have my welders 'hand brush vigorously' instead of power wire brushing. The power wire brushing just embeds or rolls over the oxides into the surface. Make sure you use the highest quality carbide burring tool as the cheaper ones will burn up fast and the metal slivers are terrible. The 'burr' will open up a discontinuity instead of embedding it. It acts like a miniature lathe.

 

[SJones]

What does the applicable corrosion testing specification say? Generally, for oil and gas work, ASTM G48 is usually supplemented by some very specific test requirements regarding such things as surface preparation and pre-test pickling, see for example, NORSOK M-601 which would not accept weld dressing irrespective of whether they would be ground in production.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[EdStainless]

An A923 is done to detect detrimental phases, and the sample must have fresh ground surfaces.
For a G48 the surfaces must be un-altered, as fabricated.
Anything that you do to the samples must be exactly what you are doing to every inch of the actual product.
Pickling is the only way to remove oxides and restore corrosion resistance.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube