[MountainBliss]

Any helpful tips and instructions for welding stainless steel sheet with arc welder would be much appreciated.

Project: 3000 liter water tank, made from stainless steel sheet, probably 14 - 17 gauge (thin). Shape of tank is round. Most seems were initially welding using ss electrode arc welding (or so it appears). Some small specially shaped parts, especially top and bottom, were TIG welded at factory before installation (tank was assembled at remote permanent site). Currently 3 seams are now leaking, with small hairline cracks or tiny pinhole sized openings.

I've been practicing on 2mm steel sheet (not Stainless), using 308l-16 electrodes; both 2.5mm and 3.2 mm thickness. (Was not able to get a hold of any similar stainless steel scrap for practice.)

One the first attempt to fix one of the leaks, a large hole (1/4 inch) was created. Apparently, I did not move the electrode fast enough. After a painstaking effort to fill it in, building weld beads on each side of the hole and working inwards (removing slag after each pass), the hole was closed and the leak fixed.

On the second leak, I tried lowest amp setting, 45amp, and moved the electrode (2.5mm) quickly, while trying to maintain liquid puddle along the way. Bead turned out multicolored, with lots of golden, blue and dark blue colorations on the bead. The bead was quite rounded in shape, like Half-Round. However, when the weld was tested for leakage, water came out from under the weld bead. Next I took a grinder and removed most of the bead. Then tried again with 55 amp setting. This time, the weld bead was flatter, but some tiny bit of water is seeping through, as if the weld bead is porous, but no water is coming out the sides of the bead. So what to do about porous weld bead? Should I grind down the second bead again? But not sure what to do with electrode settings, speed and angle for my next try. Perhaps I should try using the 3.2mm electrode at maybe 85 amp rather than minimum 70 amp to start? The wider bead created by the 3.2mm electrode should cover the first smaller bead. [In practice on ordinary steel plate (2mm thick), using a J stroke or Half-Moon stroke spreads the bead width, but I've got high anxiety of burning a hole in the SS sheet using these strokes as the underlying SS will get over heated.]

In practice, it seems holding the electrode with a 45* angle is better than say vertical angle. Does anyone agree?

When working on the 3rd leak, is it advisable to try to cover the hairline crack in one go? Or is it better to make two passes, one on each side of the crack, clean slag as best one can, then come with a 3rd pass over the top of the crack (between the previous two passes)? 2.5mm or 3.2mm stick advised?

From this forum, I understand that on vertical surfaces, starting from the bottom and moving upward is best.

Any instructional videos available?

[Otto Nobedder]

Your leaking porosity in the weld is likely occuring where the weld starts, or perhaps where it ends.

Stopping a leak that's from a crack means "stop-drilling" the crack. You should first find each end of the crack, then center-punch and drill through the vessel just beyond the edge of the crack. I'm guessing at 3000 litre, your material thickness is 11 ga. (approx 3,2mm) and at the least, 16 ga. (approx 1,6mm), so I'd use a 1/8" (3,2mm) drill bit for the stop-drill. Grind the crack about half-through, and beyond the drilled holes a good 10mm. Then start your weld at the bottom edge of your grind, and finish at the top, so that your start is 10mm below the first stop-drill, and ends 10mm above your second stop-drill.

Since you seem to have found good settings for a fairly flat weld with good color (that rainbow is a good sign for temperature), this "should" solve your problem.

If this is a simple holding tank, I see no issues with your repair. If, however, the water/vessel is pressurised, you should consult the site engineer as to whether you should be welding under a code.

Steve S

[Owr]

Welding stainless with stick is not always an easy task. If you are using a rutile type coating I would suggest you try some rutile-basic type.

The rutile coated electrodes can create a problem with fusion when you are not careful with out of position welding, probably because the weld puddle is more fluid and you overlap very easily.

On one hand you want to keep the heat input low but on the other you need good penetration and fusion. Therefore you should be careful with rod diameter and amps - for ss stick welding you often need smaller diameter rods as opposed to mild steel on the same material thickness and less amps.

With stick there is also a problem with cold starting even if using a hot start function. If allowed you can try to start the weld outside of the end of previous weld bead and the go towards that point so the heat builds up and you get proper fusion.

[Mike]

Welcome to the forum.

[MountainBliss]

Project success! Thanks to Steve S and OWR for your helpful tips and encouragement.
This forum and your help is perfect for my situation, as local welders in my remote mountain area (India) do not speak english, nor do they have SS experience. I have a lot to learn, but there is some real joy in welding metals and fixing things, making new things, etc.

Happy New Year!

[Superiorwelding]

MountainBliss,
Welcome to the family! Glad other members advise helped you in your problem. I am interested in the welding culture in India. Like most countries, I am sure we would do things differently than you and you than us. Can you share with us how it is there from a welders perspective? What is your most common process? What machine brand is most popular? Is it easy to find consumables and products compaired to here in the USA?
-Jonathan

[Rick_H]

Very interesting.....you could turn your arc welder into a scratch start tig setup possibly making future sheet metal SS repairs easier.

What kind of arc welder are you running? Nice job getting the repair done.