Source
r/metalworking•
Bools

Building a small aluminum tank for a fire dept. Thickness? Grade?

A family member has asked if I could build a small water tank out of aluminum to go on the back of their departments amphibious vehicle. The dimensions he gave puts the volume at 90 gallons. Out of the various grades, 3003, 6061, 5052, 5083 all seem like viable options depending on how much coin they want to spend but Is there one in particular that anyone would recommend for all around use? I’m unfamiliar with each grades corrosive resistance over a period of a decade or potentially more.

Also, thickness. 5/16 or 3/8 seems like it should do the job but if anyone more familiar with this kind of stuff wants to chime in that’d be great.

Posted Oct 31, 2018, 1:03 AM UTC

1712
FilthyCasual_AF•

Theoretically, 5052 should last forever as long as it's constantly wet or constantly dry. It becomes an issue when water is allowed to pool on the material and dry slowly over time. Also, I don't know what shape of tank you're imagining, but I've built fuel tanks for fishing boats and the like, and we go with 5052 as it's got good corrosion resistance and malleability in terms of not cracking when bent. To me anything over 1/4" for a tank is absolute overkill. Pro tip, if you do go with a rectangular shape, make sure to install baffles with gaps on the inside, as it will keep the side to side sloshing to a minimum.

15
EvanDaniel•

Your biggest concerns are corrosion and manufacturability.

I'd rule out 6061 on the corrosion issue, unless you anodized it afterwards. 5052 or (I think) 3003 should both be ok. But you should do some reading about the corrosion properties of those alloys in this sort of application. It's your job, and your engineering work; don't take anything us random folks on the Internet say as anything more than useful pointers in the right direction.

6
blacklungscum•

Totally read this as like a military tank

4
interiot•

A small tank though. Like an RC tank. Not plastic though, a real aluminium fire-fighting tank.

2
Zero_Ultra•

We’ve made a fuel tank out of 6061 for a small car. Would have to double check thickness, but it only held a gallon also. Baffles are good for sloshing, would be fun to simulate if you care to.

3
Dinkerdoo•

Find out what they plan to pressurize the tank to. Plug that into the pressure vessel stress equations, apply a safety factor of 3.5-6 and iterate with different material types to determine a minimum thickness requirement. I'd suggest a 5000 series aluminum for their easier formability.

2
Mentally_Displaced•

What’s the purpose of the water tank? Potable? Limited fire fighting? Other? If it is going on a Fire Dept. Vehicle for fire fighting purposes (90 gallons seems a bit small of a water supply) there may be codes governing it. If it’s for drinking or other purposes, I would suggest whatever you have the capacity to work/weld, taking into consideration the use of the water, as well as how long it will be stored and what it will be exposed to.

2
BoolsOP•

It’s not for drinking water I know that but as far as their methods, I didn’t really get into it. All I know is that this vehicle is deployed when they have a fire in the winter on one of their lake properties since the lake is frozen. It takes more time for their trucks to reach these places by road than the amphibious vehicle over the lake. It’s going to have a fill station, a pump, and will be built in such a way that more can be stored on it. I’m assuming they would use the tank for rapid deployment of water while getting their more normal operations set up and into place but I can’t be too sure.

He told me that water won’t be stored in the tank when not in use since it’s so small, it will be super easy and quick to fill. After hearing that, I was thinking I could go with either 3003 or 6160 based on cost of material while still maintaining corrosion resistance. We use 3003 regularly in our shop so I know it forms up well and welds good

1
andrewx99•

We make aircraft fuel tanks out of 5052, run some beads for extra strength.

1
c_dug•

I ask this as somebody who genuinely doesn't know the answer - why aluminium and not stainless steel?

1
custhulard•

Not op, but probably weight. Aluminum is lighter.

1
BoolsOP•

You’re right it’s a weight issue

2
[deleted]•

[deleted]

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