Seeking a chemist's input- Muratic acid vs gas tanks

[cliffrod]

in the past, I regularly used muratic acid to clean a rusty tank, neutralized it and rinsed with acetone to dry before moving on with sealing.  flash rust is inevitable but always seemed manageable.  While searching for info about sharpening vixen files, an old post on PracticalMachinist forum asserted that HCl/muratic acid used on steel would lead to permanent chemical bonding of the Chlorine to the steel and create a endless rusting-forever scenario.    SUbsequent posts claimed their HCl-sharpened files did in fact rust no matter what while other files soaked in other acids did not.

Muratic acid has been the cheap go-to for many years.  If the chlorine+steel=rust statement is valid, I would like to know.  Not planning to sharpen files with acid anyways, but I'll go a different route with tanks as well. 

Thanks in advance....

[Moparnut72]

I use muriactic acid to clean old outboard motor fuel tanks. The only issue I have had is if the tank is badly rusted enough the acid will finish the job. But then again the tank was too far gone anyway. Just use cautiously. Also remember if diluting, good idea, always add the acid to the water and not the other way around. AAA, Always Add Acid. I am surprised we can still buy it here in California as they have banned everything else.
kk

[AJ Huff]

Well it's been a long time since I used my metallurgy degree... But that's completely BS.

-AJ

[Alfetta]

Personally i use a water bath with baking soda  with an electrode in the solution and a ground wire on the tank... and leave it overnight.. next am rust is gone, dry tank and flush internal surface with acetone. then coat...

[lucky phil]

in the past, I regularly used muratic acid to clean a rusty tank, neutralized it and rinsed with acetone to dry before moving on with sealing.  flash rust is inevitable but always seemed manageable.  While searching for info about sharpening vixen files, an old post on PracticalMachinist forum asserted that HCl/muratic acid used on steel would lead to permanent chemical bonding of the Chlorine to the steel and create a endless rusting-forever scenario.    SUbsequent posts claimed their HCl-sharpened files did in fact rust no matter what while other files soaked in other acids did not.

Muratic acid has been the cheap go-to for many years.  If the chlorine+steel=rust statement is valid, I would like to know.  Not planning to sharpen files with acid anyways, but I'll go a different route with tanks as well. 

Thanks in advance....

I can't imagine it really matters if you are going to coat the tank with a sealer anyway. Rust needs oxygen and a sealed surface seals out the oxygen. I can't imagine I'd de rust a fuel tank without coating it with a tank sealer.

Ciao

[cliffrod]

Well it's been a long time since I used my metallurgy degree... But that's completely BS.

-AJ

Thanks, man.  That's what I thought as well.  The idea of "sharpening" anything with an acid bath is nuts to me.  I'm sure it creates a ragged edge that seems sharp but sounds like a great way to permanently wreck any sharp edge.  The idea of the HCl acid causing unique damage to the steel caught my attention regarding tanks.

I'm more interested in electrolysis now but have yet to do it.  I haven't had any subsequent rust-through problems using muratic acid.  My interest is more about contributing to the longevity of old parts vs speeding their demise.

[Mike Craven]

For iron (steel) maybe someone can comment on phosphoric acid and 'phosphatized.'  Iirc automotive body panels are 'phosphatized' before painting.  I always keep a gallon of phosphoric acid (Ospho) around the house for rust treatment. (I'm electrical... any further I defer)

[AJ Huff]

You can remove rust with phosphoric. Aka milk stone remover at your local Tractor Supply. Will leave behind a coating of black iron phosphate. Advantage is your steel won't have to be immediately oiled or protected in some way to keep it from surface rusting right away.

-AJ

[Cal3Me]

you don't need such a strong acid to clear out rust ,,,,,,, I cleaned 4 gas tanks this winter with straight house hold vinegar. One of which has a failed tank sealer inside. You'll get flash rust once you get the tank clean. You still need to use some chain or nails to shake around to loosen things up. Just take your time shake & wait. When the tank looks really nasty after a couple days drain the vinegar out and check things out. The vinegar is re-useable just strain out the big chunks. The best part about using vinegar is it won't harm your paint And it's way cheaper than all those other chemicals 

[moto-uno]

  One of the advantages of muriatic acid (working in bike shops for decades) is that it's fast  .
  But , boy do you want to be careful !  Peter

[larrys]

Personally i use a water bath with baking soda  with an electrode in the solution and a ground wire on the tank... and leave it overnight.. next am rust is gone, dry tank and flush internal surface with acetone. then coat...

I've cleaned rust from bike tanks and old outboard motor tanks with electrolysis. Use washing soda (sodium carbonate) instead of baking soda (sodium bicarbonate), it works better. Always remember, the positive lead from the battery charger goes on the anode not the piece you are removing the rust from. I messed that up, ONCE. Destroyed a nice old Starrett angle finder.
Larry

[Alfetta]

"Use washing soda (sodium carbonate) instead of baking soda (sodium bicarbonate), it works better."--Larry

Yes it does, but there is always baking soda (and salt) at the house, typically i buy a big bag for the pool... But this method is great at removing rust in areas that you can't get to, or even see. I used a plastic 55 gallon drum to remove a-lot of corrosion from a cross member in my Renault Dauphine, it was a formed and welded box section with many small holes open to the internal surfaces. I have to flip it as the length was longer than the drum was high, but the results was spectacular..   it would work great for bike tanks (even though i have never had to treat a tank)

[cliffrod]

I've cleaned rust from bike tanks and old outboard motor tanks with electrolysis. Use washing soda (sodium carbonate) instead of baking soda (sodium bicarbonate), it works better.

Yes it does, but there is always baking soda (and salt) at the house, typically i buy a big bag for the pool...

It's very simple to bake baking soda in an oven to convert sodium bicarbonate to sodium carbonate.   It is a convenient substitute for lye as a wash for certain baked goods like pretzels and works the same as purchased sodium carbonate while being known to be food-grade if produced using food-grade baking soda.   If you're only cleaning with it and not eating it, put some of your bulk pool or blasting sodium bicarb on a sheet pan in the oven and make what you need.

If you're making pretzels and apply excess or excessively saturated wash, you'll quickly learn not to do it.  Gastric discomfort & Farting like a racehorse do not adequately describe the aftermath....

[brider]

Always remember, the positive lead from the battery charger goes on the anode not the piece you are removing the rust from. I messed that up, ONCE. Destroyed a nice old Starrett angle finder.
Larry

I'm sure I would've made this same mistake, thanks for the tip. BTW, what is the preferred method for isolating the anode from the insides of the tank, filled with solution? OR, if the entire tank is submerged in a BIG drum, again, how do you isolate the (2) connections?

And if using a batt charger, which setting? 2-amp/hr or 6 amp/hr (on my particular charger)?

[jrt]

Gastric discomfort & Farting like a racehorse do not adequately describe the aftermath....

Hey, this is chemistry.  Biochemistry is over that way -->

[Ratso88]

When I used the electrolysis method on my "67 V700 thank I used a rubber plug that fit tight in the filler neck. Drilled holes for the anode, configured to fit the tank inside and NOT touching anything but the plug. I went with a 6 amp setting and had to set up a fan to cool the charger. Took something like three days and a few anodes, they start gathering the rust and effectiveness falls off. The overall result was VERY GOOD.

I rinsed with warm water when done. Sloshed a cup or two of Ospho around just in case, rinsed again and put the tank in the sun to dry.

Lucky me, no pin holes or leaks. Otherwise I would have coated with Caswell Tanks Sealer, I've had good results on one of my race bike tanks with this product.

Fun times. Best of luck.

PS: you'll want to slosh around some something (hand full of gravel, short drywall screws, length of chain etc, etc) to remove the loose rust first.

[LowRyter]

I suppose the idea of filling the tank with nails and shaking for 5 minutes isn't a viable solution?

[cliffrod]

I prefer a length of chain tied to a cord to help with removal.  I've had old tanks arrive with gravel, nails, nuts, bolts, washers, individual chain links and short length of chain.  Gravel and washers are the hardest to get out of the tank. 

[larrys]

Yes it does, but there is always baking soda (and salt) at the house, typically i buy a big bag for the pool... But this method is great at removing rust in areas that you can't get to, or even see. I used a plastic 55 gallon drum to remove a-lot of corrosion from a cross member in my Renault Dauphine, it was a formed and welded box section with many small holes open to the internal surfaces. I have to flip it as the length was longer than the drum was high, but the results was spectacular..   it would work great for bike tanks (even though i have never had to treat a tank)

Arm+Hammer washing soda is found in the laundry detergent aisle at the grocery store. A box will last you a lifetime.
Larry

[larrys]

And if using a batt charger, which setting? 2-amp/hr or 6 amp/hr (on my particular charger)?

Depends on the size of the piece and the size of the anode. Bigger stuff will draw more amps. I limit my charger to 4 amps so it doesn't heat up excessively. If the part and anode draw more than that, I set the charger to the 2 amp setting. I use a 5 gallon bucket and a piece of 3"x3" angle bar for small stuff. Once an anode gets good and rusty it doesn't conduct current. Have good success cleaning them with a big wire wheel on my 6" right angle grinder. Oh, do that outside... For tanks I'll suspend on string what ever piece o' steel will fit in the tank without touching the inside surface of the tank. Outboard motor tanks are easier than bike tanks.
Larry

[Road Rocket]

If you are in no hurry, molasses works nicely..Or citric acid solution..They are not hazardous and can be dumped safely…I have used The various acids mentioned but phosphoric is best in my opinion..

[RHAT]

I use ice cubes to bust up the rust,  instead of gravel and nails.
You'll want to use your cold weather gloves,  but effectively works without having to fish debris out of the tank.

[jagwillie]

Citric acid powder, readily available on the internet, does an excellent job at removing rust. It isn't toxic and can be disposed of by pouring down your drain, will not eat your skin off, or rot your lungs from the fumes. You do not need food grade. Try it, a lot simpler than some of the above methods.
Bill Bassett

[John Croucher]

Rinse with copper root kille and leave a rust free finish.

Copper sulfate for roots is commonly used to kill off root systems in plumbing drains.