Corrosion in SWG system

[Whidster]

We converted from Baquacil to a SWG system in May of 2011 and are very pleased with the results. I have been watching for any corrosion issues and until recently there were none. One of our pumps includes a loop system to the solar domestic hot water system in the garage so we can extract excess heat from that system. It has what is called a Stainless Steel, Copper Brazed Plate Heat Exchanger that the pool water passes through for heat extraction. Unfortunately it has corroded from the salty pool water which surprised me. I thought 316 stainless and copper would not corrode. I now have to replace it with a titanium heat exchanger.
This brings me to my question: is the pool water corroding the inside of my copper pipe leading to and from that heat exchanger? I am also concerned about corrosion inside the cast iron heat exchanger inside my gas pool heater as well. I have not installed a sacrificial anode to the system because I do not have any aluminum touching the pool water.
I will be able to see the inside of the copper pipe when I re-plumb the new exchanger. I can also disconnect the pvc pipe from the heater input and look inside the boiler if necessary.
Any opinions on this issue?
Thanks,
David Ableidinger

 

[JasonLion]

Copper is much more sensitive to low PH than to salt in the normal SWG range. While you do see copper pipe on older pools now and then, it really isn't recommended because it can fail quite quickly if you let the PH go too low.

316 is not really suitable for pool use even without added salt, though it will last quite a bit longer at lower salt levels. You used to see steel for filter housings. It will corrode even without added salt, but slowly enough that it was considered acceptable. However with the addition of salt slow corrosion became faster corrosion and it ceased to be considered acceptable.

 

[Safetybob]

David, from dealing with metal problems in other non-pool areas recently, and having a great talk with both my metal supplier and a neighbor who's work involves repairing/overhauling stuff outside, I found out that all that is called stainless steel isn't always stainless steel.

Number one: Unless you have the fabrication facilities yourself to make something using top notch materials, you can count on most manufactured equipment to be made just "good enough". Seems like nothing lasts like it used to? Well, it doesn't. Which is to bad for us.

Number two: Something I didn't know until a couple of years ago (because I saw 316 stainless with rust all over it) there are different grades of 316 stainless steel within the family of 316 stainless, some more "rust" resistent than others. That's ok, I had no clue either.

Now, your solution.....titanium will hopefully solve the problem (again, mass produced is mass produced) for you. From what I have gathered is that the cast iron will take alot longer to "eat away" than other stuff mainly due to it's thickness. It's wouldn't hurt to give it a good inspection and replace if it needs it. Since you have everything down, now would be the time. Additionally, from what I gather, salt or not, a cast iron pool heater will fail sooner or later.....hopefully later. How old is your pool heater? Interested to see the results of your inspection of the exchanger.

I so feel your pain as all this pool stuff gets to add up fast and the family doesn't quite understand what it takes to keep all this stuff going.

Bob E.