Any idea what metal this is? Welding options?

[Texasdoc]

I bought this tank and need to do some modifications to it. I can't figure out what metal it is made from.

[IMG][/IMG]

I thought it was stainless but it is slightly magnetic. It also is rusted at the corners and where the builder welded on the fittings.

My best guess is that it is likely a 400 series stainless since it is slightly magnetic. I figure the welding was not appropriately gas shielded and destroyed the stainless-ness of the metal.

Since the stainless properties are already ruined (its starting to rust where it was welded when it was made), I can get some Stainless Flux Core wire (Blue Demon 308LFC-O) and do what I need to do. I can then paint the outside with Rustoleum and seal the inside of the tank to stop rust (KBS coatings tank sealer).

Any other thoughts?

[just dreamin]

My thoughts, for what they are worth. Use a shielding gas as well as the flux core wire and give the tank coating a miss as it is another potential problem area if it doesn't bond. The rust concern although valid, is not a going to be a greater issue than what is there now, and should not grow as it is only caused by the welding heat that alloys the two metals.
My experience is only personal as I am not a certified welder, so feel free to disregard it.

[joyridin']

If it is 400 series SS, it will be magnetic. Only 300 and some 200 series are non-magnetic. Most OEM exhaust systems are 400 series and they rust over time. The rust is no big issue as it would take years and years before it became unstable. I have seen 30 year old car exhausts in salty Ohio look fine and just the steel flanges rot off.

You will be fine using it. Not paint needed inside or outside. Nothing will rust and flake off like you see in steel.

[redmt]

I would TIG weld it with a dual regulator. The second Argon line inside the tank set at around 10 cfm. Use a gaslense cup, 3/32 %02 Lanthanated and weld your heart out.

[Texasdoc]

Yeah, I don't have a TIG. I have a MIG (or flux). I can't find anywhere to buy sheet stainless locally, so I'll have to order it online. I can get carbon steel to patch the big hole in the top at ACE or HD, but I'm not sure I want to mix metals. I may just have to find a local fabricator and pay them to TIG some stainless over it.

[redmt]

The problem you may find is that not many fab shops will weld on a gas tank. If I was to do it, I would first flush with plain water then add some dishwasher detergent ( that stuff cuts anything) Fill the tank with a gallon or so of water and shake the snot out of it. Rinse and repeat. Let it sun dry and then see if you have any hint of fuel smell. If so do it again. You would have to purge the tank of any fumes to weld it no matter how you do it.
If your going to try and mig weld it I would look into a dual shield wire and then still flow purge gas into the tank while welding.
On a guess by the time you buy wire and a stainless patch piece it would be cheaper to find someone to weld it at a shop. You will still have to have it super clean before they would even touch it. Be prepared to pay $5.00 or more per inch of weld. I would have a $50.00 minimum for just your reference.

[legenmetals]

The four hundred series stainless is an alloy of Chrome and steel and very little nickel, if any. The nickel is what reduces oxidation and causes the non-magnetic quality of 300 series stainless steel.

Weld it and coat it with paint.

[Texasdoc]

Originally Posted by legenmetals

Weld it and coat it with paint.

If I did this, do I need to worry about rust on the inside?

[joyridin']

Not if you use 400 series SS. It will not rust.

I have welded this material hundreds of times. I would not use flux core wire, but if you have a mig welder with a gas mix, grab some 400 series SS from Ebay, weld it up, and forget about it. You will never have a problem. I would not even worry about painting it unless you want it to look pretty.

I welded baffles in my tank a few years ago. Washed it out with soapy water (Dawn dishwashing liquid), then welded away. I had no problems whatsoever.

[Texasdoc]

Since I don't need it to be magnetic, can I just use a 300/316 series stainless? I am still assuming this is 400 series - it is slightly magnetic. It may even just be steel. I'm not sure how to tell.

Edit: I found this on a welding website.

If the tube is martensitic or ferritic, the magnet should stick just as well as it would to carbon steel. If it is only slightly attracted, I would guess you have austenitic tube there, probably 304. 304 is the most susceptable to martensite transformation during cold working. The strain placed on the tube while forming the sheet into a tube probably transformed some of the austenite into martensite which you are picking up with your magnet.

So, I think I probably have a 300 series stainless. Looking at the photo in the first post, the welds around the plugs have rusted a bit but the tank hasn't. There isn't any surface rust either. So I think the tank is stainless. Since a magnet barely sticks, I don't think it would be ferritic or martensitic.

I'm going to go buy a sheet of 300 and go to town. (Someone hold my beer....)

[joyridin']

It will weld up fine. You will not have any issues.

[cycleguy55]

Originally Posted by Texasdoc

If I did this, do I need to worry about rust on the inside?

If you're concerned you could always coat it with POR-15 before you button it up and install it: https://www.por15.com/POR-15-Fuel-Tank-Repair-Kit

[Hoodabest]

Originally Posted by cycleguy55

If you're concerned you could always coat it with POR-15 before you button it up and install it: https://www.por15.com/POR-15-Fuel-Tank-Repair-Kit

I really like por15 paint, but be skeptical of any gas tank sealer currently available to consumers. In my other life (vintage motorcycles) I've come to the conclusion that sealants fail most of the time and make a big mess.

Recommend PURGE the tank with argon (not co2) and tig weld. Inert purge prevents any scale from forming inside the tank. Good luck.

[Texasdoc]

I purchased a sheet of 16g 304 stainless. Pre-cut to fit the hole I was patching. I used Blue Demon 308LFC-O flux core stainless welding wire that doesn't need shielding gas. It welded up well. Painted the outside then sealed the inside with KBS coatings tank sealer. I took my time and followed the directions explicitly. It turned out better than I thought it would. If it fails, I'll just get a fuel cell replacement.

Overall, I'm pleased with the results.

[GREENSNAKE]

Stainless steel