[Aleksi86]

So if anyone can tell me facts for oxidation when welding 3mm stainless steel 316L whit 316L filler 98%Argon and 2% co2.
Im gona weld ss tank truck whic is used to drive dangerous liquids. I weld it both sides first out then in. And they are welded somehow like this: First tack weld inside,then welded out side whit so much Volts/Amps that it will come trough on inside where are tack welds. After that its weld outside we grind inside clean bright metal and open that root 1,5mm-2mm whit 2mm cutting wheel. Im worry about that root because can it damage base metal Groove too eaven we grind that oxidation off,but can it leave contamination?? That "welds" what is coming trough is bretty big at least 4mm . It looks bretty solid metal when its grind and not like tig root (whit out gas coverage)..So would it be better to weld colder to have less root coming trough. We had two X-rays and there was litle bit root what was not melted eaven it had come so much through at first weld and then weld other side, so that got me doubt is something wrong and that mistake was midle of that weld no stop/start Place or any porosity before that.. And here are litle info 115-125Amps 20-21,5V wire speed 6,8m-7,2m no backing gas on root.

[Superiorwelding]

So if anyone can tell me facts for oxidation when welding 3mm stainless steel 316L whit 316L filler 98%Argon and 2% co2.
Im gona weld ss tank truck whic is used to drive dangerous liquids. I weld it both sides first out then in. And they are welded somehow like this: First tack weld inside,then welded out side whit so much Volts/Amps that it will come trough on inside where are tack welds. After that its weld outside we grind inside clean bright metal and open that root 1,5mm-2mm whit 2mm cutting wheel. Im worry about that root because can it damage base metal Groove too eaven we grind that oxidation off,but can it leave contamination?? That "welds" what is coming trough is bretty big at least 4mm . It looks bretty solid metal when its grind and not like tig root (whit out gas coverage)..So would it be better to weld colder to have less root coming trough. We had two X-rays and there was litle bit root what was not melted eaven it had come so much through at first weld and then weld other side, so that got me doubt is something wrong and that mistake was midle of that weld no stop/start Place or any porosity before that.. And here are litle info 115-125Amps 20-21,5V wire speed 6,8m-7,2m no backing gas on root.

Ok I will give it a shot. If I am understand this correctly you are welding a butt weld and are burning through on the back side or "sugaring". You then grind this sugaring off to clean bright metal on the inside and lay a pass on the inside.
I am sure others here will chime in and might be able to answer better but here is what I think. The sugaring on the back side is a very bad thing. There are several things happening here, one of which is a loss of chromium and your corrosion resistance. The second is the fact that the HAZ might have oxidized therefore doing you no good. I know you are grinding it down but I might be concerned about trapping some "junk" in the weld and having problems in the future. In my opinion if this were food grade it would be a no, no.
Why can't you use some tape on the back side or some copper? Even aluminum foil would be better than nothing. I have had success with the foil on very thin SS.
What do you others think?
-Jonathan





AWS - A5.9-93

[dirtmidget33]

I was always told sugaring is bad changes the corrosion resistant properties of the stainless. since you can get to the back side to grind and clean it why not use SolarfluxB if you don't want to back purge. It would have to be cleaned off and vacuumed up but seems better to me than having the welds sugar and grind that out and then your not sure of what is really going on in that bead.

might want to read some posts in TIG section there is a member there that has posts and pics of tanker trucks that carry liquid gas I believe where he repairs cracks and corrosion cracks from what I seen pretty cool stuff he welds on.

just my .02 cents in no way qualified to weld on tanks carrying hazmat.

[Aleksi86]

That base metal contamination im mainly worry about,because lack of fusion what showed on Xray doesen make sence to me whit that much root opening and welding both sides.. I just started to Think If that oxidation eaven its grind off makes uneaven melting on base metal.. Like you weld over a tack thats gray and Budle kind of rejects that... And im speaking about 60m welds were the xrays Will be taken.. I have to study about this more to avoid failed x-Rays because wrong methods.. Im just still new my job and youngest welder,so i cant go teach my boss or older welders... I hope Steve.S or JODY could Tell they thoots???

[Otto Nobedder]

I hadn't commented yet, as I don't MIG these welds. Not that it can't or shouldn't be done, but because the client's WPS specifies TIG with backpurge. I'd be reluctant to use Solarflux B, also, because of the clean-up, and the oxygen-clean standards we have to meet.

In general, for a two-sided butt-weld with full penetration, I weld the first side with a goal of no more than 80% penetration, to reduce the heat-affected zone and potential sugaring. This leaves less grinding work on the back-side, as well, allowing you to grind an even groove with a 7mm (1/4") grinding disk, edge-on. I find an even groove like this easier to fill consistently.

Bear in mind, while I've had success with this method, it's never been on anything critical, so it's never been x-rayed, and I've not even done a coupon for bend-test, so take it for what it's worth.

I, too, would like to hear others' thoughts on this, including Jody's.

Steve S

[Aleksi86]

Heres a picture so thoos cross sections will allways be x-rayd an overall therewill be taken quit many of them,when it builds up.. Other pic is inside look of my "office" about 10m long and 2.2m high

But you get the point that there is lots of places to make mistake on welds if its not done correct..

[Otto Nobedder]

No baffles... So a light liquid, like liquid hydrogen.

Are you building for Aire Liquide? BOC?

Steve S

[Otto Nobedder]

The uniquely weak point in that vessel is where the longitudinal welds meet the circumferential welds (where the lines meet the circles). Proper tie-in is the challenge. This is because each end of a "barrel section" is a start/stop point for a weld, which must be right for the circumference weld (butt weld of each barrel section) to be flawless at the point they meet. My company has such a good reputation, that they didn't believe me when I found a leak in a vessel we built, but it can and does happen, and I showed them the evidence with a picture of a dye-penetrant test. This was a weld that had passed x-ray when built.

Just some general comments on what's being built...

Steve S

[weldin mike 27]

Hey,

I agree with Otto, Reducing the amount of penetraion is a good way to reduce your troubles, most easily by reducing the bevel on the plate/ sheet, from a feather or small land to a wider one that can be "back ground" later to enable full penetration. Failing that, get of make some perforated tube and bend it around the circumference of the tank and tape it there to enable an argon purge.

Mick