Leaking TIG welds on Rock Valley tank

[Marty G Cars]

First of all this tank has been modified and is not a defect from Rock Valley. I had to have the tank notched to clear the rear mounts for my rear leaf spring mounts and now the TIG welds are leaking. Is there any way to repair these welds once fuel has been put into the tank? I'm afraid that even after draining the fuel and rinsing out with water that there will still be fumes that may ignite. Any ideas?

[sinned]

Flush it real well with water and leave it full of water during the weld process.

[BRIAN]

Bring it to a certified welder so you don't kill yourself......and so it won't leak.

[Matt@RFR]

Just a note: Don't assume that a certified weldor knows what they're doing. Cert's mean that you are qualified to run specific parameters on specific materials in a specific position, that's it. Buyer beware.

[MrQuick]

Dennis are you trying to get the guy electrocuted?? LOL
Just drain it, let sit for a few days the flush with water, let sit for a few days then go to town.... you can use a shop vac to rush the process.
I've never finished the tanks I do, usually gets tacked up then sent to a rad shop for finish brazing and sealer.
Works for me

[Matt@RFR]

What Dennis described is the generally excepted way to do it. Job shops don't have a couple days to wait.

A safer variation is to fill the tank with Argon, which dissplaces oxygen just like the water does.

For small tanks that you can clamp in a vice and that have an adequately sized 'vent', I've been known to throw a match in the tank and just get it over with. (Do not try this at home!) Whoooooosh! and you're ready to weld.

[CDJr]

Or you can fill it with water, then empty it and all fumes should be gone.

"Welders: The only people that think a co-worker catching on fire is funny" <---I laugh every dam time I read that, Matt.

[Marty G Cars]

Thanks for the responses. The shop I took it to is usually pretty good with their results and I'm sure that they will fix it for free. I have also noticed that there is rust (?) around the new TIG welds. How can this be on a stainless tank?

[paul67]

Also wants its flushed put a pipe from the back of your car into the tank and run it the fumes from the car kill the fuel fumes left in the tank.
paul67

[Matt@RFR]

I have also noticed that there is rust (?) around the new TIG welds. How can this be on a stainless tank?

You need another weldor. Two things cause a stainless weld to rust:

1) Too much amperage/voltage. If this is the case, I bet the welds were flat grey, right? Overheating stainless reduces it's corrosion resistance badly. Stainless welds should be shiny (TIG) and have colors like silver, gold, blue, orange and purple. Some of those colors are right on the brink of being too hot, but still exceptable in something like this. Also, a flat grey appearence tells you that the weld is very brittle. It might have passed a pressure test new, but with vibration, it could have cracked, causing your leak.

2) When stainless comes in contact with steel, it can get contaminated, and the iron deposits left frm the steel will rust. Same thing with aluminum. In your case, it was probably one of two things, if not both: A wire brush that was A) not stainless, or B) used on steel prior. Second likelyhood was a 3M hand pad used on mild steel prior.

Here's a clue for everybody: If you take ANYTHING to a shop to get welded and noone asks you what alloy it is....pick it up and take it somewhere else with a quickness.

[parsonsj]

Matt,
Good stuff. I find your welding tips about color to be very very useful, and apply them to all my work.

Is it possible that the weldor used standard steel rod instead of stainless rod? Can you determine that from looking at the weld?

jp

[Bigblue73]

Heres a cure for the rust on the welds of your tank. The effect area of the weld which turns colors is from the inpurities that are in the metal (all stainless is not equal, try chinese or russian stainless once!), tig wire and basically dirt that is on the tank. We use a product called UTP Beizpaste CF pickling paste. The pickling paste removes the discoloration and some of the impuraties from the weld. The product is about 20% Nitric Acid. The other solution is a passivation tank. The process involves cleaning the tank with a acid (caustic) cleaner to remove any grease, then dipping the part for a period of time (based on time and temperature of the solution) in a nitric acid bath. After dipping the tank is rinsed and cleaned and left to set for 24 hours. Stainless steel builds it's own oxide layer to resist rust. The nitric acid will eat away the ferrous deposits in the metal.

[Matt@RFR]

John, thanks.

Yeah, that's possible, and for something none critical that'll get some type of coating, it's ok to do in a pinch. I've found that you'll still get the color since the filler and the base metal mix, but it's a dilluted mix so the colors aren't as previlent.

To answer your question though, I don't know if you could tell by looking at a weld if mild steel filler was used on stainless. I doubt it, especially considering the hugely varying techniques weldors use.

[Matt@RFR]

Pickling is great, but it won't do anything for this case if the rust was caused by the weldor running way too hot. Will pickling solve rust that's allready there?

Also, it may be alittle tough to pickle a fuel tank at home.

[Marty G Cars]

Pickle? Hmmm ... I think I'll go make me a sandwich.

[Bigblue73]

We, I'm talking from our fabrication shop side, have had a few problems with fabricating stainless steel items for the food industry where "embedded" ferrous material has been present. It's caused by the handling of materials sheets, it just happens from time to time. Food equipment cleaner (caustic) will immediately show the rust. It's embarassing to be called by a client where you both can stand there and watch the machine rust in front of you. Not real pretty getting your ass chewed for something that can be corrected early on.

We have found the passivation dipping process works the best to remove the embedded ferrous. It's simply dissolves into solution and does not effect the stainless steel. We use the pickling paste to clean the welds with a stainless steel brush. All the discoloration is removed easily.

What are you welding with, a MIG or TIG? If your are getting really bad discoloration, what are you using as a sheilding gas? Argon? Are you preparing the material before you weld?

[Matt@RFR]

What are you welding with, a MIG or TIG? If your are getting really bad discoloration, what are you using as a sheilding gas? Argon? Are you preparing the material before you weld?

Thanks for the responses. The shop I took it to...

Are there any pictures of the welds? Too much guessing here.

[Marty G Cars]

Here are some pics

[paul67]

What about removing the modifed stainless and getting it done again but about 1/4 " bigger to get rid of contaminated area, the tanks got to come out what ever you do. Cut the bits out your self to save cost ago somewhere else to be fabbed and welded looking at it couple hrs at the most for the fab and weld .
paul67

[BRIAN]

What I was getting at with looking for a cerified welder was simply this is not a backyard repair. There are liability issues. Bring it to a capable shop and let them prep it to how they want it prepped for welding. This way there is some type of warranty and the liability issue is off your head and on theirs.


I like doing everything myself but have learned you can't be the best at everything. This is not an area where you would want to come up short. Good luck.... and by the way simply pressure test the next repair before installing it. Saves a big mess.