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topic 60268

Aluminum piping underground. How to do corrosion protection?

Current question and answers:

January 6, 2021

I hope this thread isn't too old as I have a similar question.
My team is developing a cast aluminum water pipe product which will be buried in the ground. Anodizing and e-coating are options that have been brought up for us but I'm not finding definitive information as to how effective these will be in protecting the 319 or 356 aluminum buried in a variety of soils, and my experience in this area is limited.
Is electroless nickel an option, and between the listed options, do you have an opinion what would give the longest life?
This is a new product, and our customer uses stainless steel and ductile iron, but this particular product has very ambitious mass targets, and our analysis so far shows that a lightweight alloy is the only option. Thanks in advance for the help. -Tom

Thomas Vaeretti
- Bessemer Alabama
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January 2021

A. Too old? We have threads here from Electronic BBS days, 5 years before the Internet existed :-)

Electroless nickel is very expensive, but maybe not in comparison to stainless steel pipe. But it leaves you with the problem that if the coating is penetrated, you have a very strong corrosion couple between nickel and aluminum to accelerate the corrosion; I don't think it's a good idea at all. Anodizing probably won't hurt anything, nor will e-coating.

A very quick googling revealed that aluminum culvert manufacturers use two different grades of aluminum clad together, and that when aluminum pipe is used for irrigation systems it is supposed to be taped on the outside whereas the copper content of the water which can be handled on the inside is limited.

Personal opinions posted here are fine, but it appears that there is some established history with aluminum pipe underground which should be reviewed. There may well be finishing consultants or piping consultants already very familiar with the issues, and there may be applicable codes or standards. Good luck.

Luck & Regards,

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January 11, 2021

thumbs up sign Thank you Ted for your reply.
The product we're developing is a cast aluminum part buried in the ground with pipe, but not a pipe in itself, so cladding is probably out of the question. It's good to understand the pitfalls of nickel. Sounds like e-coat or anodizing are going to be our best bet. Your input is appreciated greatly!

Tom Vaeretti [returning]
- Bessemer Alabama


January 2021

A. Just one more thought. Magnesium sacrificial anodes might be a possibility or, if your device is electrical, even an impressed current corrosion prevention system such as used on boats.

Luck & Regards,

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Previous closely related Q&A's starting in:

September 8, 2016

Q. I am the inventor of a new ground source heat exchanger and will be manufacturing same. I need to know if zinc chromate will add corrosion resistance to my 6061 aluminum pipe to increase the life of the heat exchanger in the ground. The earth will be between 4.5 and 8.0 pH and have a low electrical conductivity.

Dan Halloran
ground heat exchangers - Charleston West Virginia USA
^- Reply to this post -^


September 2016

A. Hi Dan. Series 5xxx aluminum would probably have some corrosion resistance but, if you can afford it, electroless nickel plating will have better conductivity and much greater corrosion resistance than chromate conversion coating; but will accelerate the corrosion if breached.

Regards,

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Ed. note Jan 2021: Did some quick googling and see that there is some history available of aluminum pipe underground. So studying that may be a better first step than blue skying :-)


September 14, 2016

A. At the variable pH you describe, chromate will be almost worthless.

In fact, aluminum won't last a long time at either of those pH extremes.

Use a good grade of stainless like 316, or use black cast iron. Either will last for decades, maybe generations.

jeffrey holmes
Jeffrey Holmes, CEF
Spartanburg, South Carolina


September 19, 2016

thumbs up signJeff, Thank you for your reply. I was also going to add a coating of tar (bitumen) that, while reducing the thermal conductivity some, won't hurt the overall performance... Stainless and cast iron are out of the question.

Dan Halloran [returning]
ground heat exchangers - Charleston West Virginia USA

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