Sunday, August 26, 2007
I got an e-mail another Pool Guy the other day. He said, “Hey Pool Guy. What’s the story? You haven’t bashed salt in over two weeks. But my salt pools are still falling apart at warp speed. Case in point:” and he attached a zip file with these photos in it.
This first one shows the remains of the brass inserts that are pressed into the plastic frame of the Polaris 280 so that you can mount your axles onto the frame via stainless steel screws.
The next one shows the Polaris cleaner frame that these brass inserts pulled out of.
This next one shows what one of the axle frame mounts that hadn’t corroded away yet looks like for contrast.
You can see on the first picture that there are remnants of the brass inserts remaining in the holes, and it’s depth matches right up with what you’re seeing on what’s left of those brass inserts in the first picture.
This photo here shows what I think is most interesting. It’s the picture of the two screws and the frame to axle reinforcement plate.
Take a close look at the screw on the left. See how the threads appear to have a brass colored look to them? That’s because they’re coated with brass. Not in that cross-thread, softer metal looses sort of way. In that four years of Galvanic Corrosion sucking off brass electrons and plating the stainless steel with them sort of way. Because this is The Textbook Example of Galvanic Corrosion.
Here’s what Dr. Stephen C. Dexter, Professor of Applied Science and Marine Biology said in an article from the University Delaware Sea Grant Marine Advisory Service MAS NOTES:
“Galvanic corrosion, often misnamed ‘electrolysis,’ is one common form of corrosion in marine environments. It occurs when two (or more) dissimilar metals are brought into electrical contact under water. When a galvanic couple forms, one of the metals in the couple becomes the anode and corrodes faster than it would all by itself, while the other becomes the cathode and corrodes slower than it would alone. Either (or both) metal in the couple may or may not corrode by itself (themselves) in seawater. When contact with a dissimilar metal is made, however, the self-corrosion rates will change: corrosion of the anode will accelerate; corrosion of the cathode will decelerate or even stop."
MAS Notes is a Marine Advisory Service program sponsored by the University of Delaware and NOAA, the National Oceanic and Atmospheric Administration, an agency of the United States Government.
So, you have a tough decisions to make. Who you gonna believe? The scientists, funded by our government to spend their whole lives studying these types of corrosion mechanisms? Or, your Local Salt Sales Rep?
If you chose B, well, thank you for playing. On your way out, please sign up for our next reality based program called “If I Only Had a Brain”.
And believe me, if it hadn’t coated that stainless screw like that, then when that Whacky Salt Rep who likes to call me names writes in, he’d be able to give me the old, “very interesting, Pool Guy, we’ll need to see the water chemistry records for that pool and for every pool everywhere for the last thirty-five years to make sure that blah, blah, blah, blah….” [read, “so we don’t have to admit any liability for our ever more failing technology.”]
And speaking of Failing Technology, that reminds me to say that I was contacted by the Canadian Broadcasting Company this week. Seems they’re working on a story about why the Wave Pool in Calgary is closed until February and wanted to know what I thought were the reasons. I told them what I thought was going on behind those closed doors with Canadian taxpayer’s dollars, and made sure they knew whose salt system it was that’s installed there so they could get a comment from the manufacturer on why their salt system had done two million six hundred thousand dollars – Yes. That’s right. $2,600,000.00 – worth of damage to the Wave Pool in 2 years and 8 months – Yes. That’s right. Thirty-two months.
But I’m getting off the subject. What afflicts the Wave Pool is just plain old fashioned salt spray corrosion. The kind that’s not supposed to happen in 3,500 parts per million (ppm) salt water because it’s “less than the salinity of a tear” and “ten times lower than the level of salt in seawater”, and a whole bunch of other nonsensical things I could say if I were trying to sell these things instead of reveal the truth about them.
What we’re talking about today is Galvanic Corrosion. Now, don’t confuse that with Stray Current Corrosion. That’s another whole different kind of corrosion that salt water brings to your pool and that kind afflicts those metal things that are tied to the pool’s bonding grid – which is pretty much everything except these automatic cleaners and stainless steel filter tanks and the stainless through rods that hold your DE filters together. Pay close attention the next time you’re cleaning a salt pool’s DE filter that uses those knurled brass screws on the stainless through rods. I bet the screws will be Missing In Action, or on their way to being gone. But on the up side, as Dr. Dexter pointed out, the stainless steel is now actually stronger. Here’s a table that shows how that works:
The Anodic end is the end that deteriorates. Look down the list and find brass. Then look further down the list, toward the Cathodic or Noble end and look for stainless steel. See? First, it lists 300 series and then way down, it lists 400 series stainless steel. In fact, all stainless steels are more Cathodic, or more Noble than brass.
The only comfort in the whole situation is that the Polaris frame has something like a 5 year warranty. So, if you’re lucky, your wheels will fall off before the five years is up. This customer’s did.
But, you know how it is. You start taking a Polaris apart to ship the frame back for exchange, and this is true for any of the Return Side Cleaners, and unless the wheel bearings are pretty new, they’re going to disintegrate in your hands. Then, when you get into the guts of it, you’re probably going to notice that the salt has eaten up the teeth of the driveshaft, like I showed you HERE, and that the driveshaft bearings are welded by corrosion to the driveshaft splines. And, of course, you might as well put on new tires and wheels while you’re into it…
What’s a Mother to do?
Stay away from salt. That’s my advise.
Labels: Salt and Metal Parts