Author Topic: Stainless Steel gas tank.  (Read 17258 times)

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Offline Peter Jack

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Re: Stainless Steel gas tank.
« Reply #15 on: February 09, 2015, 08:38:40 PM »
On second thought, that really isn't a good application for Solar Flux. The glass like residue might break away and go where it shouldn't.  :-( :-( :-(
I've been known to use the Solar Flux in exhaust systems where it works really well.

Pete

Offline tauruck

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Re: Stainless Steel gas tank.
« Reply #16 on: February 09, 2015, 08:46:55 PM »
Pete, your advice is always on the money.
Thank you for the update. I've never used flux
but am willing to learn and do what it takes.

When you work with composites all day the welding
is a welcome break. I love it and hope to get better
at it. The welding on the exhausts I did is fine according
to the guy that built the Dakar truck. How bad does the SS
warp?.
I never do a full pass anyway but when the tank is done
I don't want it looking like junk.

Offline Peter Jack

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Re: Stainless Steel gas tank.
« Reply #17 on: February 09, 2015, 11:52:06 PM »
"How bad does the SS warp?"

That's why you use lots of small tacks. Practice on some scrap before you start on the real thing.

Pete

Offline tallguy

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Re: Stainless Steel gas tank.
« Reply #18 on: February 10, 2015, 01:29:19 AM »
Here's an answer from a weldor (this is the correct spelling) and mechanical
engineer (with a concentration in welding/metallurgy) of many years.

Stainless steel distorts a LOT from welding.  Here's why:

Shortly after it was discovered (by accident, after somebody melted some
chromium and mild steel together . . . the resulting alloy didn't rust very
much at all), it was learned that this material resisted heat pretty well.
In other words, it retained some impressively-high strength even while hot.
So the name "heat-resisting steel" was applied and generally used.  But
in common applications such as cooking utensils and liquid containers, where
strength is not as important as chemical inertness, the word "stainless" became
a major marketing tool.  

Back to the concept of "heat-resisting" . . .  If you can imagine red-hot steel
having about two percent of the strength of steel at room temperature, then you
know that heating the steel makes it quite easy to bend.  I think most or all of
us have done this.  Stainless steel, by contrast, maintains much more of its
strength even while red-hot.  This is why many industrial components are made
of it, for use in hot environments.  Stainless steel at 1200 degrees F may have
somewhere around 20 percent of its room-temperature strength.  

Now, consider a weld cooling and shrinking as it cools.  A weld made of stainless
steel, as it cools (while still red-hot) will pull harder than a red-hot weld made
of mild (regular, common) steel.  For this reason, stainless steel has a reputation
for "pulling like a m-f" when the weld cools.  In some instances, one can compensate
for this by fixturing geometrically "biased" so that after the weldment is taken out
of the fixture, "springback" can pull the weldment into the desired configuration.  An
example might be as follows:  If you want to weld two flat plates together to form
an "L" shaped weldment, maybe they should be clamped so the angle between them
is about 92 degrees (obtuse) on the side where a fillet weld will be.  When the weldment
cools, it will pull about 2 degrees, closing that 92-degree angle to about 90 degrees.

As mentioned in earlier posts, lots and lots of small tack welds will help.  Welding both
sides of the material will also help, alternating from one side to the other (even in tack
welding).  But this may not always be practical, as in the case of a small fuel tank.  The
tank could be designed so that welding can be done on the inside and the outside of major
subweldments, before the final welding is done (on the outside only of the last seam) to
join the subweldments together, resulting in the final weldment.

For a fuel tank, here are my suggestions . . . 1. Use fairly thick stainless steel, since in
land speed racing, you don't need to be too concerned about weight -- at least compared
to aerodynamic drag and other friction.  Also, use stainless filler material and add it while
welding (instead of simply melting the sheets together).*    2.  If the walls will be flat and
distortion would be a big issue (usually for esthetics only, in my opinion), you could add
stiffener ribs on the inside or outside of the walls before the walls are welded together.*

I also agree strongly that "back-purging" with argon is a wonderful idea, instead of using
any kind of flux.  Don't try to save money by using any other gas for this purging, as it
works best with argon.  I can explain later why.  There is a lot of experience available
from others.  Please consult them.  Even purging with argon can be done wrong, so
ask for details about argon flow rate, and "scavenging" during initial purging.  And I also
strongly suggest using a gas lens on your GTAW (formerly called "TIG") welding torch.  
*You could ask me for more (e-mailed) details if you want, on all of this.
« Last Edit: February 10, 2015, 01:34:57 AM by tallguy »

Offline tauruck

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Re: Stainless Steel gas tank.
« Reply #19 on: February 10, 2015, 06:08:47 AM »
Thanks Tallguy, that was awesome. :cheers: :cheers: :cheers:

I really appreciate the explanation.
This tank project is going to test me.

I'll do some more thinking and planning before I dive in.

Mike.

Offline manta22

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Re: Stainless Steel gas tank.
« Reply #20 on: February 10, 2015, 11:47:19 AM »
Mike;

Consider using a nickel silver braze weld for stainless steel. It has far less distortion than fusion welding since the stainless is not heated high enough to melt a weld puddle. It also does not need argon shielding, relying instead on a high temperature flux.

I like to use Harris #17FC rod with its corresponding flux. I paint both outside & inside surfaces with flux and then heat the stainless to a low red heat with a neutral oxy- acetylene torch. The rod melts on the surface of the stainless and by controlling the heat and direction of the torch, you can control where it flows. With a little less heat, it melts but doesn't flow much at all, allowing you to form a bead. The flux is removed by hot water (so they say) but a phosphoric acid solution helps.

The resulting joint (preferably a lap joint with close fit) has very high strength- about 80,000psi, and the distortion is quite low compared to fusion welding. This is NOT brazing like one normally associates with brass alloys.

Regards, Neil  Tucson, AZ
Regards, Neil  Tucson, AZ

Offline fordboy628

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Re: Stainless Steel gas tank.
« Reply #21 on: February 10, 2015, 12:40:22 PM »
Mike;

Consider using a nickel silver braze weld for stainless steel. It has far less distortion than fusion welding since the stainless is not heated high enough to melt a weld puddle. It also does not need argon shielding, relying instead on a high temperature flux.

I like to use Harris #17FC rod with its corresponding flux. I paint both outside & inside surfaces with flux and then heat the stainless to a low red heat with a neutral oxy- acetylene torch. The rod melts on the surface of the stainless and by controlling the heat and direction of the torch, you can control where it flows. With a little less heat, it melts but doesn't flow much at all, allowing you to form a bead. The flux is removed by hot water (so they say) but a phosphoric acid solution helps.

The resulting joint (preferably a lap joint with close fit) has very high strength- about 80,000psi, and the distortion is quite low compared to fusion welding. This is NOT brazing like one normally associates with brass alloys.

Regards, Neil  Tucson, AZ

LOTS of early British chassis were jig made steel tubing brazed together with nickel silver rod and a "bubbler" fluxer filled with the liquid flux.

ONLY the welder knows if the joint is properly made, but with a bit of practice good joints can be done.     You do need to practice to prevent "cold shuts" which do not adhere well to the parent metal.

I've seen the mild steel/low carbon steel tubes tear before a properly made joint will fail.    80,000 psi is much higher strength than low carbon steels.
 :cheers:
Fordboy
Science, NOT Magic . . . .

I used to be a people person.  But people changed that relationship.

"There is nothing permanent except change."    Heraclitus

"Only two things are infinite, the universe and human stupidity, and I'm not sure about the former."     Albert Einstein

Offline tauruck

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Re: Stainless Steel gas tank.
« Reply #22 on: February 14, 2015, 10:49:16 AM »
Guys, I'm building a 1100mm wide bending break.
Nothing fancy and built from off cuts and general junk
that gathers.

It isn't done and I'm giving someone Mig lessons so the
neatness isn't tops.

Offline tauruck

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Re: Stainless Steel gas tank.
« Reply #23 on: February 14, 2015, 10:51:20 AM »
I bent some 2mm mild steel over the mandrel which is 1"
using pressure from the vice.

Offline tauruck

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Re: Stainless Steel gas tank.
« Reply #24 on: February 14, 2015, 10:54:36 AM »
I've got this new filler cap.
Never used but had it a while.
I'm thinking of using it but you guys might have
opinions I'd like to hear.

Going to use the bending break to shape some Stainless for the tank.

Looks like we're using 1,6mm?????.

Offline manta22

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Re: Stainless Steel gas tank.
« Reply #25 on: February 14, 2015, 11:06:01 AM »
Looks good, Mike. I'd add a small ear under one of the bolts and drill a hole in it so that the cap could be safety wired closed. It is a tight cap but safety wire adds an extra layer of security.

Regards, Neil  Tucson, AZ
Regards, Neil  Tucson, AZ

Offline tauruck

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Re: Stainless Steel gas tank.
« Reply #26 on: February 14, 2015, 08:24:14 PM »
Thanks Neil. I do have a bunch of new blind anchor nuts with a yellow seal.
I know they are aviation spec. I'm thinking of using those instead of the stuff
supplied with the cap. I'll wire that sucker good for sure!!!.

The cap looks OK but has a cork seal????. It came on a plastic tank I bought
from Summit a long time ago. I changed it out in favour of a quick release cap
I found in an airplane junk yard. I don't trust that cap either due to its age,
condition.

I'll be running Ethanol and I'm not sure how the cork holds up.
What do you think?. :cheers:


Offline tallguy

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Re: Stainless Steel gas tank.
« Reply #27 on: February 14, 2015, 11:11:09 PM »
I wouldn't rely on cork, as it's made of a bunch of small (natural) chunks of bark stuck
together with who-knows-what.

There are lots of nice (rubber) materials available that can resist chemical effects
(dissolving, for example) of various chemicals such as alcohols.  I'd use rubber.  Gasket
companies can custom-fab for you if you want, as well as providing advice on a suitable
material.

Sometimes it's good to pay the experts for their experience/knowledge.

And by the way, please don't forget to provide for venting, to allow air to enter
the tank as fuel is consumed.  You wouldn't want to buckle the tank or starve your
engine, I assume.   And if you do go with the experts (gasket company), please be
aware that once the setup for fabbing one gasket is done, the subsequent (second,
third, etc.) gaskets are relatively inexpensive.   I'd buy several, as spares, and keep
them stored in ziplok bags, away from sunlight -- which is harmful to some types of
plastic/rubber.
« Last Edit: February 14, 2015, 11:16:44 PM by tallguy »

Offline RaceEngineer

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Re: Stainless Steel gas tank.
« Reply #28 on: February 14, 2015, 11:39:56 PM »
Make sure the vent is adequately sized.  I would add, it is advisable to use a tip over valve at the tank to minimize spillage/leakage if the vehicle flips over also use a  filter on the vent line to limit contamination of the fuel tank (ie. dirt, salt , etc)

Regards

Don   

Offline tauruck

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Re: Stainless Steel gas tank.
« Reply #29 on: February 15, 2015, 08:57:24 AM »
Tallguy and Don, thanks for offering advice.
I really appreciate your input. :cheers: :cheers: :cheers:

One of my sponsors is a rubber gasket manufacturer so I'll hand over the cork
and have them make a real gasket.
The cork was a concern and you also came to that conclusion.
The tip over valve will have to be something special. The filler is a big one
and I'll investigate and revert back.
The vent line is a done deal. I've been there before but all the input helps.
Thanks again.