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oldcorollas
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January 2003

Re: Steel ~ What type to use for this application?

Tue, 17 February 2004 11:49

long and short of it, 304L or 316L.

SeptemberSquallIndustries wrote on Tue, 17 February 2004 20:36

Hi,
I need a sheet steel which meets the following requirements;
Must resist petrol exposure.
Must resist weather exposure (ie. water).
Must be weldable with MIG.
Any ideas what commonly available steel I should look at? Would galvanised steel sheet be okay or would it oxidise?

afaik, most metals resist petrol exposure... unless there are acidic or basic additives to assist corrosion.

weather exposure is a bit more tricky. almost all materials are affected by weather exposure, just some more and some less. this is also a problem if you get any moisture in the inside of the tank which will sit under the petrol and cause corrosion from the inside.
good stainless steels (with enough chromium content) will do a pretty good job.

weldable with mig rules out most aluminium alloys, and you don't really need any fancy 6000 or 7000 series anyways (ie heat treated for strength) you just need thickness for strength, since weight is not imperative.

i would rule out steel to start with. galvanised is terrible to weld and it needs to be recoated.. i don't fancy dipping a whole fuel tank is liquid zinc tho... nor do i like the consequences of metal fume fever when welded Wink

low aluminium content steels (like in exhaust tubing, or other materials like Kanthal) are good, but weldability is a problem. the welds will be susceptible to corrosion.

what i would recommend, if you want to do it yourself, would be to use something like 304L stainless (18/8 to 18/20 chromium nickel, with low carbon) which is readily weldable IF you use the correct filler wire for 304L. it is readily available also.
http://www.assda.asn.au/304.html
it is not recommended for temps above 50 or 60 degrees where it wil come into contact with chlorides (ie salt) or it can suffer from 'stress corrosion cracking'.

the next choice is 316L, (16/10 to 18/14, but with 2-3% molybdenum). it is a bit stronger and has higher corrosion resistance. it is harder to cut, but is almost as easy to weld as 304L (as long as it is low carbon version -L )
the only downside to it is extra cost (due to the moly, extra nickel, and is not used quite as much as 304)
http://www.assda.asn.au/316.html

304L and 316L will cost you around 4-7 times the same in mild steel, and you will need MIG wire that is specifically for the alloy (ie 304L or 316L wire) AND you will need a suitable sheilding gas (ask BOC or LINDE for their recommendations), AND you will need to have a bit of practice to make sure you can do consistent welds with no pore, pinholes or gaps... would suck to have a shiny tank that leaks.

really your only other option is aluminium alloy, but it would HAVE to be TIG'd for best results. it does not have the same corrosion resistance, and can have corrosion occuring inside the tank if any water is trapped below the fuel...

for my money i'd go 304L. if i was feeling fancy and wanted the tank to lats almost forever, i'd go 316L. if it was for a race app, and weight was huge factor, i might go aluminium alloy..
i will be using 304L for mine later (and for my surge tank)

Ti?? could use it, but oh the cost!! i have a sheet of 3mm thick Ti-6al-4V at uni... cost more than i'd like to mention.. too much for a fuel tank anyways Wink

and the heat treatment cost... etc etc.. ouch.

Cya, Stewart

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