Anyone using an aluminum tank for pressurized storage?

[patch53]

My buddy just called me back and can make me a 450 gallon aluminum storage tank for about $1200, including all fittings. I'd like to go bigger, but just don't have the room in the basment for anything bigger than that.

Pat

 

[henfruit]

hey pat, will your tank be pressurized? round or ??? size.

 

[patch53]

hey pat, will your tank be pressurized? round or ??? size.

Pressurized. Rectangular, 6' tall X 4' wide X 30 inches deep should = about 450 gallons. Gotta be under 32 inches deep to get thru a doorway.

 

[henfruit]

sounds like my plan . but iwant more gallons.

 

[patch53]

sounds like my plan . but iwant more gallons.

Me too :-/ What size wall thickness are you planning on using? My guy suggested 3/16" with angle welded on in 3-4 places for support.

Pat

 

[Fred61]

If there is going to be any copper in your system you had better not use any aluminum in any part of it. Same with galvanized fittings. It will all corrode due to the dissimilar metals. I'm sure people that know more about it tnan I will chime in when they log in and see your headline.

 

[patch53]

If there is going to be any copper in your system you had better not use any aluminum in any part of it. Same with galvanized fittings. It will all corrode due to the dissimilar metals. I'm sure people that know more about it tnan I will chime in when they log in and see your headline.

Yeah, you have to watch out for galvanic reactions. With aluminum as the "base" metal and with aluminum fittings, you can connect galvanized to it without too much trouble, copper would be a no-no. Aluminum and galvanized are fairly compatible metals according to the chart. I then plan on using di-electric unions to go from galvanized to copper. There should be no problem coming in from the boiler to the tank with Pex.

Pat

 

[Tennman]

What kind of pressure are you talking? Just a 2' diameter surface in the middle of one side will have over a 2,000# load at only 5 psi. Flat sided pressure vessels try to make themselves round. Pressure vessels are typically round so the vessel's wall is only in tension. If there is much of any pressure, a flat sided pressure vessel will require someone to do some simple beam analysis on the stiffeners. Not trying to rain on a parade but you could end up wasting a bunch of money or getting hurt.

 

[hayrack]

Don't use any galvanized fittings. Galvanized will destroy your circ pumps. You should be able to find a used propane tank for little or nothing.

 

[henfruit]

Hey pat i think we need to do some re thinking? or use them not pressurized.

 

[patch53]

What kind of pressure are you talking? Just a 2' diameter surface in the middle of one side will have over a 2,000# load at only 5 psi. Flat sided pressure vessels try to make themselves round. Pressure vessels are typically round so the vessel's wall is only in tension. If there is much of any pressure, a flat sided pressure vessel will require someone to do some simple beam analysis on the stiffeners. Not trying to rain on a parade but you could end up wasting a bunch of money or getting hurt.

Pressure would probably be in the 15-20 PSI area. The guy who would be building the tank was supposed to check on what type of bracing and support the tank would need to withstand the weight and pressure. But yes, it is critical that it be able to take the pressure. Thanks.

Pat

 

[patch53]

Don't use any galvanized fittings. Galvanized will destroy your circ pumps. You should be able to find a used propane tank for little or nothing.

Really? Never heard about that before. I had a few galvanized fittings on my old system with my Aquatherm for 7 years and never had a circulator problem. Can anyone else shed any light on this?

Can't use a propane tank, couldn't fit it in the basement

thx, Pat

 

[patch53]

Hey pat i think we need to do some re thinking? or use them not pressurized.

LOL, yeah, these guys are shooting all kinds of holes in our plans ! I'm going with pressurized, one way or another.

Pat

 

[tom in maine]

Speaking from some experience--any time aluminum winds up in a heating system with copper or steel, corrosion ensues.

If you use it, just plan on having a good floor drain and/or a means of unplugging plugged up piping.

Every couple years someone comes out with an aluminum baseboard or some other aluminum plumbing item. They disappear rather quickly
as things go bad. Corrosion inhibitor might mitigate some of this, but if you need to do a pressure system, stay with steel or stainless.

 

[patch53]

Hi Tom, from what I understand about galvanic reactions and compatibility is that a lot of it depends on what the dominant material is. Aluminum is easily corroded when in contact with many materials if it is not the dominant material. For instance, I have an aluminum dock on the lake where I live that has SS fasteners. Those SS bolts have been on there for 10 years and the aluminum around them is not the slightest bit corroded, even the ones in contact with the water, because the aluminum is in much greater quantity than the SS. If it were the other way around, the aluminum bolts would probably be long gone by now.

Now, if I have an aluminum tank with aluminum fittings connected to a dielectric union and then to copper pipe I wouldn't think I would get any corrosion problems? I don't know for sure, maybe I'm all wet here. If anyone knows for sure please let me know. I appreciate all the input from you guys, and I will certainly look into it further before proceeding with this project. the last thing I want is to have major corrosion problems down the road.

thx Pat

 

[tom in maine]

Hi Pat,
My experience is that dielectric unions solely delay the inevitable. There is a lot going on when you start moving water through metals that are dissimilar.
If aluminum worked without incidence in plumbing systems we would see a lot of it in use given its advantages in weight and cost.
It has been used in solar systems and other systems and does eventually start to break down.

You might get away with aluminum if it was the only metal in the system, but that is not usually the case.

I got nipped once with a convector that used aluminum as a turbulator in a brass fitting. It turned to a concrete-like corrosion product that ruined the convector.
After that I have seen solar systems that used aluminum as a tank (they all failed). Solar collectors with aluminum absorbers and dielectric fittings which had a bunch of pinholes.
And a lot of aluminum baseboards that all eventually failed. These baseboards keep showing up every couple years (once the memory of the previous failures are murky) with a new alloy that eventually lets go.

I suspect the tanks that do work are used with inert metals or plastic in situations that are less aggressive (cooler temps.)

I have read about some aluminum solar collectors (online postings) that have stood the test of time. I am sure there are exceptions. I avoid aluminum in any heating system like the plague.
Except for enclosures (we use it as a facer on our tanks!)

It might be worth a try, but it would have to be really inexpensive to take the risk.
It is a risk that I would not want.
Tom

 

[patch53]

Thanks Tom, you know a heck of a lot more about this than I do. I think I'll take your advice and look for another alternative.

Oh well, back to the drawing board ! LOL

thx again, Pat

 

[RobC]

Patch if your man can weld aluminum can't he do steel ( get rid of the door that has Mr Murphy's name on it ) ? There was just a post on rectangular tanks and bracing etc. At least you'd be eliminating the potential for galvanic action. If you did go alum look into using a zinc anode as sacrificial material. I think some DHW tanks have them but I have no idea on the bonding for this set up.
If you looked into "marine bonding and sacrificial anodes" you could get lots of info. Granted you're equipment won't be in salt water (electrolyte) where there's higher conductivity. However the higher the water temp the more potential for conductivity except for pure water. Here's a small bit from a boats US paper. Note last line especially.....

Galvanic corrosion continually affects all underwater aluminum, but at a reduced rate when no dissimilar metals are connected to your aluminum parts. When in contact with an electrolyte, most metals form small anodes and cathodes on their surfaces due to such things as alloy segregation, impurities, or cold working.
We have used stainless steel (cathode) and aluminum (anode) in this discussion as an example, however other metals coupled with aluminum also produce galvanic corrosion cells. For example, zinc connected to aluminum will form a corrosion cell, but in this case, the aluminum becomes the cathode and the zinc (anode) corrodes. One of the worst couples with an aluminum drive would be connecting it with copper or a copper alloy (bronze).

Rob

 

[DaveBP]

Patch, you do realize that at 20 PSI the 6' x 4' wall of that tank is going to have nearly 70,000 lbs. of force bulging it out, don't you? And the same nearly 70,000 lbs. on the opposite wall in the opposite direction. And the other walls proportionally. Please fill it nearly full of water when you pressure test it, not just air.

 

[patch53]

Thanks Guys, gonna have to re-think the whole deal here.

Pat

 

[peakbagger]

If you are building a tank thats intended to operate over 15 PSI, it is a "pressure vessel" and therefore will have to be designed to ASME code in many states and possibly registered and inspected. Even if the state isnt a "code" state, its still a good idea to build to ASME code as the reason it was written many years ago was to keep pressurized vessels from failing. I have see the results of air tanks failing, and its isnt pretty. There is a lot of potential energy that builds up when a tank is under pressure and when it lets loose, this energy has to go somewhere and frequently thats through a wall or a floor. If you are lucky it just springs a leak and floods the basement. Niether option is something I would voluntarilly introduce to a house.

 

[Gooserider]

I have done a fair bit of research into water cooled computers, which have many of the same issues, except on a MUCH smaller scale... If you go to any of the sites where people play with liquid cooling, you will find endless tales of bad experience w/ mixed metal systems. Most common mixed metal combo is a copper radiator (automotive heater core) and an aluminum CPU cooler block (because copper is a bear to machine...) Even using plastic pipes to connect things, and distilled water for filling, the aluminum blocks have failed in as little as just a few months due to dissimilar metal corrosion problems.

IMHO it is a bad idea to have ANY kind of aluminum in a hydronic system, no matter how it is conducted. Remember that it does no good to use dielectric couplings, or plastic pipe to make connections, as the WATER ITSELF is a conductor (even distilled, tap water or water with any kind of boiler conditioner chemicals in it will be worse...)

Gooserider

 

[heaterman]

Not a good choice. Aluminum in a system introduces a whole 'nuther set of circumstances as far as dissimilar metals go. It also makes a fantastic anode for any and I mean ANY stray electrical current that may be present.

In addition, judging from the dimensions you gave, I doubt the tank is rated for any pressure. If you use it, be prepared with mops and buckets. Even at 10PSI you are tlaking about tremendous force on the sides of the tank when you calculate the total area involved.

The only way i would consider using it would be unpressurized and filled with a treated fluid that is monitored at least every 6 months. Rho-Mar makes an all metals boiler antifreeze that has an excellent inhibitor package and would probably work but you are talking BIG $,$$$.$$ to fill a vessel that size with it. I would advise finding a plan B.

Some of the boiler companies in Europe use Aluminum HX's in their gas fired heating boilers and from what I hear expected life is in the 6-10 year range. Weil-McClain is using an aluminum block in their high efficiency boiler here in the US and from what I hear through the grapevine there are issues. They just released a service bulletin advising owners to use a water treatment package, sold by them, in all installs both new and existing. Warranty is void if not used. ........draw your own conclusions. IMHO there is no good reason to use aluminum in any hydronic heating system.

 

[dirttracker]

FWIW, we had a vacuum chamber built at work to perform electrical tests at a simulated altitude. The chamber was intende to be good to at least 70,000 ft altitude equivalent pressure. It's a cube about 40 inches on a side, the walls are 1 inch thick 6061-T651 aluminum plate. For electrical and fluid pass through connection areas we used 1.25 inch thick Lexan. I've seen this chamber go to ~1 psia, an equivalent pressure differential of ~13.5 psi inside to outside. Based on this construction, I think you will need thicker walls for your pressure tank. Even if it's made of steel, 3/16 starts looking pretty thin when you consider the forces.

As everyone else has said, aluminum and copper don't mix with a water heating system. I've been involved in designing aluminum heat exchangers to run with liquid cooling systems. Even with corrosion inhibitor, using aluminum and copper with any water based working fluid (usually propylene or ethylene glycol based) is a bad idea. This goes double at high temperatures, like where you would run a heating system. The last propylene glycol/water system we set up, we had to go through every piece of equipment that would ever come in contact with one of the heat exchangers and make sure there was no copper anywhere in the system. Even to the point of using nickel brazed flat plate heat exchangers in our test equipment instead of copper brazed flat plates. If there was any copper present, the filters would plug with blueish-grey paste.

 

[heaterman]

FWIW, we had a vacuum chamber built at work to perform electrical tests at a simulated altitude. The chamber was intende to be good to at least 70,000 ft altitude equivalent pressure. It's a cube about 40 inches on a side, the walls are 1 inch thick 6061-T651 aluminum plate. For electrical and fluid pass through connection areas we used 1.25 inch thick Lexan. I've seen this chamber go to ~1 psia, an equivalent pressure differential of ~13.5 psi inside to outside. Based on this construction, I think you will need thicker walls for your pressure tank. Even if it's made of steel, 3/16 starts looking pretty thin when you consider the forces.

As everyone else has said, aluminum and copper don't mix with a water heating system. I've been involved in designing aluminum heat exchangers to run with liquid cooling systems. Even with corrosion inhibitor, using aluminum and copper with any water based working fluid (usually propylene or ethylene glycol based) is a bad idea. This goes double at high temperatures, like where you would run a heating system. The last propylene glycol/water system we set up, we had to go through every piece of equipment that would ever come in contact with one of the heat exchangers and make sure there was no copper anywhere in the system. Even to the point of using nickel brazed flat plate heat exchangers in our test equipment instead of copper brazed flat plates. If there was any copper present, the filters would plug with blueish-grey paste.

Exactly

It's a multitude of information like this that really makes me wonder what the heck some of the boiler manufacturers are doing with AL heat exchangers on their product. I think a lot of people that buy these things are in for a surprise. Should maybe move some or all of this thread into the gas and oil fired area.