Phosphoric acid in gas tank

[Luca]

After getting lousy results with the first step of my por-15 hd cycle tank repair kit, I decided to not bother with lining products and instead just treat with phosphoric acid-specifically klean-strip phosphoric etch and prep diluted to half strength: 20% +/-2.5% after dilution.  I left it in overnight and briefly had the tank inverted so I could cover all surfaces.

Not only did it do a great job on the rust, but it did a better job of removing cruddy old liner than the POR stripper.  However, after rinsing the tank out and starting to dry it I'm getting flash rust all over the inside of the tank.

I thought I was supposed to be getting a protective, rust resistant coating of iron phosphate on the inside of my tank.  What gives?  Does it need more time or a stronger concentration?  Should I not be rinsing with water?  Some products such as ospho say they leave a zinc phosphate coating.  Do I need something like that?

Any suggestions towards a rust free tank would be appreciated.

[Bob_Roller]

I experienced the same thing when I relined three fuel tanks .
Advice to members that may engage in relining their fuel tanks .
First, don't waste the $50+ or so on the POR kit .
I purchased just the POR liner material for about $30US for their small can, more than enough to do a motorcycle tank .
I'll have to search for the receipt for the liner for the company, it was about $15 for the liner and $15 Hazardous Material shipping .
If your tank is really rusty, the chemicals in the kit won't do the job of getting the tank rust free .
I've used common household vinegar for rust removal, it takes a few weeks, so be patient if you go this route .
I used phosphoric acid after the vinegar, and got the same flash rusting on all three tanks .
I don't know if using something other than water to get the remaining residual acid out of the tank, would remove / dissipate the acid or not .
I used the POR lining ' paint ' and at least up to now, have not had any lining come loose .
The Guzzi was done 7 years ago .
The '82 and '84 LS's, were done 6 years ago and no issues with them either .
While I have not used this product, I hear good reviews about Caswell epoxy tank liner .
So, Luca I don't think this is going to be an issue for you, based on my experience .


http://www.amazon.com/POR-15-49216-U-S-Standard-Sealer/dp/B00B3HXCZ4



This is the company I purchased from a few years ago .
I don't think the free shipping applies to this product .

http://www.tcpglobal.com/POR-49216_2.html#.Vxe7j1L2aM9

[Justin B.]

The inside of the tank on my '81 R100 was very rusty and giving it a good soak in muriatic acid seemed to get rid of all of it.  I think this was about 14 years ago...

[Tony Smith]

The inside of the tank on my '81 R100 was very rusty and giving it a good soak in muriatic acid seemed to get rid of all of it.

For those who live in different parts of the globe
Muriatic acid = Hydrochloric acid = swimming pool acid.

Your swimming pool supply is the cheapest source. It is fantastic for de-rusting steel, be aware though that any steel cleaned  cleaned with muriatic acid will flash rust

[Motu]

I've had POR-15 tank liner in my TLR200 for over 14 years, so it holds up well...no leaks yet.  

[skippyc]

I had a problem getting a seal for a RV cooper engine, i could get something close but needed to remove the steel around it so i put it in Muriatic - hydrochloric acid and it dissolved the steel and i was able to fit the seal with glue. it's still working.

So I guess it's buyer beware.

[Luca]

Once the POR stripper didn't work I had second thoughts about getting all the liner out and properly prepping the metal, so I decided to go with phosphoric acid just so I could take care of any rust that was in the tank and hopefully leave a rust preventative coating in its place rather than put an epoxy liner in at all.

It's the elusive iron phosphate or something similar that I'm after, so that I can have a tank sans-flash rust without putting a liner in at all.

[Bob_Roller]

If you don't want to put a liner in the tank, try using the phosphoric acid to remove the flash rust, then instead of using water, use paint thinner, mineral spirits, to rinse out the tank .

[Tony Smith]

If you don't want to put a liner in the tank, try using the phosphoric acid to remove the flash rust, then instead of using water, use paint thinner, mineral spirits, to rinse out the tank .

That's how I remember it - Acid to shift the rust, Phosphoric to covert the flash rust to hard Iron Phosphate and then rinse with water.

To dry the tank, either run a vacuum cleaner (in "blow" mode) into it for several hours or, and this cunning trick was only taught to me recently by a master painter, get two 12V blinker/tail light  bulbs in basic festoon fittigns and hang one each side of the central "spine" of the tank and connect to a 12V power source (a 4amp battery charger works fine). After about 8 to 12 hours the gentle heat from the bulbs will dry out the entuire tank, ready for coating with a lining paint or with a epoxy sealer.

The second tip the old painter gave me was to use paint if the the tank was sound and to only use an epoxy if the tank leaks due to rusting in the seams.

The third tip he gave me (and this is truly gold) was as follows - whether you use paint or epoxy you simpl;y cannot get all the excess out, there will always be a thick "blob" left that will never fully harden - and if you are tryign to seal leaks int he tank this is a disaster if the "blob" is at the bottom. The hot tip therefore is that once you have swilled the paint of epoxy about and covered all of the tank, and then drained as much excess out as you can, turn the tank over and leave it to dry on its back - the "blob" is then on the top surface of the tan where it can do no harm whatsoever.

[Luca]

Well I've changed course again. Since I have the kit, I'm getting flash rusting, and I've already lost enough riding this season with my tank on the laundry counter, I'm just going to put in the POR liner and be done with it.

I've done a bit more soaking with my Klean Strip phosphoric acid to get rid of the liner on the top of the tank.  Now I'll rinse it out and do the POR 3 step system.  Wash with their cleaner degreaser, etch with their metal prep (which will leave a zinc phosphate layer), and then thoroughly dry and coat with the epoxy.

I've designed and printed an adapter/diffuser with my new 3d printer that holds a hair dryer in the mouth of the tank for drying.  The only real worry I have now is making sure I get a good epoxy coating on the overflow pipe that goes through the inside of the tank.

I just found my camera the other day so I'll try to take a few photos of the operation.