Anodized Aluminum In Swimming Pool Environment

[DFLewis]

Is a MIL-A-8625F hard anodized finish overkill for preventing corrosion in a swimming pool environment? Would a less thick anodization such as MIL-A-8625 TYPE 1 or 2 hold up as well?

We're looking into anodizing a 2' X 2' X 8' Aluminum 6061-T6 tubular member truss. It will not be submerged but will occasionally be splashed with chlorinated water and is constantly exposed to small amounts of trichloramine from the air.

Thank you in advance for your suggestions and comments.



DFLewis

http://www.phoenix-engineer.com

 

[TVP]

It would be better to use one of the conventional anodized finishes like Type II that have been sealed instead of hard anodizing. Hard anodizing is for improving wear resistance, and is generally not sealed, which means that it has inferior corrosion resistance. There are also issues with crazing that can penetrate through almost the entire thickness. Any high quality anodizer like IHC or Pioneer Metal Finishing should be capable of producing what you need. Out of curiosity, is there a reason you aren't investigating organic/paint coatings?

 

[SEdelman]

TVP,

I hate to post as a brand new user, but I am struggling with an almost identical situation.

An architect has specified metal skimmer lids for the deck next to a pool. They come in Aluminum and Bronze but he wants them to match the other pool fittings, primarily the stainless steel handrail.

I've located various tints that profess to match the color of stainless a concern was raised that anodizing would not stand up to use around a pool because it would be seriously damaged if any concentrated chlorine powder or liquid was to accidentally come into contact.

I've asked the vendor to consider supplying the lids in stainless, but it isn't clear they can or will in which event I'm stuck trying to come up with some way to make either Aluminum or Bronze work.

We had metal sample made up that was powder coated but it looked terrible so whether that is some sort of coating to keep them bright, or at least protect them against corrosion, anodization or chrome I don't know (any suggestions would be very much appreciated).

Here is the product web site...

http://www.skimmerlid.com

Thanks.

 

[DFLewis]

My efforts have stalled on determining what will work best in this environment for aluminum. We've moved on to other items that beg our attention. From what I've read, TVP is correct on hard anodizing's primary use and benefits. Being on the pool deck, I would be primarily concerned with wearing off any coating or finish. Which I think alludes to the use of a hard anodize aluminum if the chemical reactivity issue isn't a problem.

Good Luck.

DFLewis

http://www.phoenix-engineer.com

 

[KENAT]

SEdelman, while a related topic, a new post might be appropriate.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

 

[SEdelman]

I almost started a new thread but since the problems were so closely related if not essentially identical (how to protect aluminum in a swimming pool environment) in the end I thought it would work better if they stayed together.

It was a judgement call and I'll try and do better next time.

 

[SEdelman]

DFLewis,

I've had an idea that might help you. Swimming pool covers generally use aluminum tracks and frames. One would think therefore if anyone knew about how to protect aluminum it would be these guys. You might take a look at one of their sites and see what they do. If you can't find anything I could give a jingle to the manufacturer who is supplying our job and see what he specs. I'm sure he'll tell me.

My problem is a bit different because we are trying to match the look of stainless steel, but for what its worth electroless nickel is coming highly recommended.

 

[KENAT]

I nearly suggested electroless nicke for you SEdelman, but I don't know how tough it is.

We use it a reasonable amount where I am but I believe mostly for aesthetic reasons.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

http://eng-tips.com/market.cfm?

 

[SEdelman]

DFLewis,

I was wondering what you ended up deciding on for a coating?

Steve

 

[EdStainless]

You are correct, EN will look more like SS.
But with either anodize or plating the key is the sealer. They will need to be sealed, and this will require periodic replacement.
The most critical factor is to make sure that these are installed so that water cannot stand on them. Drainage is everything with pool hardware.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[SEdelman]

Since my application is a skimmer lid there is no question but that they will be subject to significant amounts of standing water both chlorinated from the pool (primarily in the summer) and rainwater.

If EN plated Aluminum isn't able to stand up to that then perhaps a better choice is to go with stainless steel. Downside is the vendor is quoting triple the price for each lid set, almost $600 each.

 

[btrueblood]

Do you have to use 60xx alloy for the skimmer lid, or could you use a more corrosion-resistant alloy like 5052 or 5054?

 

[SEdelman]

I'd need to check with the vendor to see what he is using as his default (the Aluminum skimmer lid is a stock part while the stainless would be a custom run just for us).

Ideally I'd go with brushed aluminum, no plating at all if there was an alloy that wouldn't corrode when used in a pool deck. Its cheaper, lighter and looks fine. The only issue is how it will stand up to the pool water.

Assuming he can give me a choice which alloy would you recommend?