Aluminum suitable for saltwater service? 3

[hp32e]

I am designing a 1200 gallon atmospheric tank for storing liquid brine (26% NaCl in water) at ambient temperature. We are fabricators and do not want to outsource plastic tanks. I'm considering 5052 type, 0.25 inch plate for the welded shell and flat bottom (immersion zones). I'd like to see 20 years of service life. Does anyone have experience with saltwater applications using marine grade aluminum and is this material suitable for continuous immersion service?

 

[boo1]

you will have to coat it

 

[moltenmetal]

A 1200 gallon blow-molded HDPE tank will be cheaper than the aluminum to make your tank.

 

[SJones]

26% NaCl is not "marine."

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[racookpe1978]

How many do you need to make?
1200 gals isn't very big - open top or something somebody can get inside of to pray-coat with epoxy or fiberglass resin?
Does it have to move, or is it fixed in place?
Room temperature indoors, or inside/outside with sunlight and freezing problems?

 

[metengr]

HDPE

 

[winstonsk]

I'd avoid the aluminum. At the very least, you'd have to babysit it--coatings, cathodic protection, inspections, etc.

Just buy HDPE. You can fabricate an Al shell for it

 

[hp32e]

I was hoping to hear from someone with actual experience: good or bad. I've decided to perform a simulation test. Of course, this will take some time, so HDPE will suffice for now.

In response to some of the comments:

If successful, we would continue to use aluminum for tanks much larger than 1200 gallons.

We can build an aluminum tank faster and for less cost than purchasing an equivalent plastic or fiberglass version. When it comes to custom nozzles, manways, lifting lugs, hold down anchors and other attachments, the molded plastic and FRP tanks cost too much and take too long to deliver (if you can get a custom tank at all).

Aluminum oxide (that forms insitu) is a protective coating that might be impervious to saltwater.

Thanks to all for your input.

 

[boo1]

I did provide my experiences.
Uncoated will not last 20 years, it will pit.

 

[moltenmetal]

HDPE will last, aluminum will not. So there you have it.

 

[SnTMan]

hp32e, I'd listen to these guys

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[EdStainless]

I have seen Al tanks hold up 10 years in clean, treated seawater service. Then during an inspection someone drops a steel tool on the floor, and month later there are pits through the bottom.


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P.E. Metallurgy, Plymouth Tube

 

[metengr]

Come on ....as best stated above, 26% NaCl (brine) is NOT sea water.

 

[EdStainless]

Once you get over a couple % NaCl concentration doesn't really matter as long as the temps are low.
Where it does matter is at the water line. In brine you will get some evaporation and a solid salt deposit, corrosion there can be fierce.

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P.E. Metallurgy, Plymouth Tube

 

[WKTaylor]

A couple of references to ponder...

ASTM B928 Standard Specification for High Magnesium Aluminum-Alloy Products for Marine Service and Similar Environments1
......
From The Aluminum Association, Aluminum Design Manual 2015, states following...
2.4.6 Ships
1. ANSI/AWS D3.7-2004 Guide for Aluminum Hull Welding, American Welding Society, Inc., Miami, FL, 2004.
2. Rules for Building and Classing Aluminum Vessels, American Bureau of Shipping, Houston, TX, 1996.

2.4.7 Storage Tanks, Pressure Vessels, and Pipe
1. ASME B31.3-2012, Process Piping, American Society of Mechanical Engineers, New York, NY, 2012.
2. ASME Boiler and Pressure Vessel Code, Section II, Materials, American Society of Mechanical Engineers, New York, NY, 2013.
3. API Standard 620, Design and Construction of Large, Welded, Low-Pressure Storage Tanks, 11th ed., American Petroleum Institute, Washington, DC, February 2008.
4. API Standard 650, Welded Tanks for Oil Storage, 11th ed., American Petroleum Institute, Washington, DC, June 2007. Appendix AL addresses aluminum storage tanks.
5. Aluminum Alloys for Cryogenic Applications, Aluminum Association, Washington, DC, 1999.

NOTES.
a. I imagine that sour crude oil is pretty abusive to metals... and often contains water.
b. Affects of bio-contaminates are another separate issue.
c. I suspect that a high quality rubberized-seal coating could be applied to the interior surfaces of welded storage tank for a significant improvement in corrosion resistance due to Isolation. Obviously, the exterior should be primed and top-coated for general protection.



Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]

 

[WKTaylor]

OH YEAH... and maybe install a sacrificial anode rod... like what is installed on most deep-sea platforms

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]