Building a gas tank, have a question

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jmlcolorado

Well-known member
Joined
Jul 23, 2010
Messages
1,839
Location
The flat plains of Elbert County, CO
Guys,
I'm building a gas tank for the rat. I'm using 16 gauge steel for it. I have all the pieces cut and edges cleaned to bare metal.
Question is, before I go and tig this whole thing together, do I need to remove all the milling oil on the inside sides of each panel?
Is it really going to matter?
Also, should I coat the inside of the tank with something after I have it all done or will the bare metal be okay?
I know motorcycle tanks last a dang long time with them as bare metal, but I also always see guys coating the insides too.

Another question is do I need to remove the milling oil at the Inside edges of each panel prior to tig welding? I'll be welding all the corners together from the outside and I have those edges cleaned already.
 
I would clean the inside edges as well. A proper weld will penetrate all the way through to the other side, effectively pulling anything left there other than bare metal in and contaminating the weld. It's just good insurance, especially on a tank.

Me personally, I would leave the mill scale on the inside and NOT use any aftermarket coatings. They will all fail sooner or later, and when they do you have a mess on your hands and usually a ruined tank. Do good welds and pressure test it afterwards. Done...
 
I would clean the inside edges as well. A proper weld will penetrate all the way through to the other side, effectively pulling anything left there other than bare metal in and contaminating the weld. It's just good insurance, especially on a tank.

Me personally, I would leave the mill scale on the inside and NOT use any aftermarket coatings. They will all fail sooner or later, and when they do you have a mess on your hands and usually a ruined tank. Do good welds and pressure test it afterwards. Done...

Good to hear my brain is on the right track.
I'm tacking all the edges (cleaned) on the inside with my mig. I will be going to my buddy's house and tig'ing the outside later.
I'm thinking I'll only put 1 weld in bung for the fuel pickup line. It'll be threaded with NPT threads so I plan on using that port to install a fitting and pressure test.

What's a good pressure to test at?
The initial test will be @ 5 lbs, then cover all edges with soapy water to look for bubbles. I'd really like to do a final test with a pressure gauge at maybe 10 lbs and let it sit for 24 hours and see where it's at.


I don't have a filler cap in mind yet. I was going to do a flush mount top cap like a fuel cell, but now im leaning towards actually doing a neck to the side of the truck with a vented cap. I don't really trust a vented cap at the top of the tank.


The pickup tube will weld to the threaded bung inside, then drop to the bottom and curl it up so it's 1/2" off the bottom of the tank so as not to pick up contaminants.
Would it be beneficial to do a small sump at the very bottom or is that overkill?

I will be adding 2 baffles inside to help with slosh.
 
Take it easy with the pressure. 5 lbs is enough. 10 lbs or more can turn your new tank into a blowfish. :eek:

I would test it twice. If it's good with air and soapy water, do a "hydrostatic" test. Fill it with water and add 3-5 lbs pressure. A bicycle pump works good for this. Give the water 10-15 mins. under pressure. if it doesn't leak, you're good. If it leaks, you can repair it without gasoline vapor. When all is good, rinse the tank with methyl hydrate.

That might sound stupid, or a little extreme, but that's how we tested petroleum tankers when I was in that industry. You can always find a water leak. Air, not so obvious.
 
We build tanks, a lot of tanks. About 600 so far.
We use 14 ga hot rolled sheet. Most all the tanks are made in just 2 parts and they interlock like a big clam shell. This saves 1/2 of the welding and cuts way down on warpage problems.All the edges are ground clean, and we grind back about 1/4" to make sure we have a clean base metal. The 2 parts are tacked about every 4" all over, then we mig weld both ends first then the 2 long sides last. After it cools we install the fuel outlet, and or drop tube if it feeds from the top. Then it is pressure tested at 10-12 PSI. We use windex to check for leaks. It does not leave a soap slime all over the tank and helps to clean the out side. Repair any small leaks and keep checking. To date we have not had any tanks come back for leaks after they were installed and filled with gas.
 
Did I miss mention of a fuel gauge sending unit? I am using a tank from RPM, which fit perfect. I coated the inside with a sealer from a cycle shop. I think it was Creame. I cut the neck off the old tank and migged it onto the new one.
If you have enough room you can use rubber hose and clamps for a filler and cap attachment.
 

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