I've had to replace two expansion tanks in four years on my secondary loop of my Geo system. This loop is water only for a radiant floor system. I am using soft hot water for make-up through a B&G pressure reducer valve. The pinhole leak rusty water indicating internal corrosion. Should I look for a stainless tank or some kind of corrosion inhibitor in the water loop? Or is this indicative of some other problem? Thanks!
Wow that was an eye opener! I checked the radiant loop (while circulating) at a spigot near the expansion tank. pH = 12- 13!!! using wide range paper. I immediately checked the pH of the water at the well source (~6 to 7) and pH of soft hot water make up supply ( ~8 ) Clearly something is going on in the loop that is greatly increasing the pH of the water. I tested the hardness of the make up water and it was about 8 - 9 grains. I'm sure the unsoftened water is liquid rock with a hardness in the 20's ( well) Theres also a lot of iron in the water. I'm chemist but I'm not a boiler/geo expert. What is running up the pH? Do I need some kind of ion exchange on the loop or some additive? Thanks for the help!
All wrong. I was thinking acidic. For basic systems, I would suggest you have too much air entering your system somehow. And you basically have rust happening.
What do you think about stainless expansion tanks or additives? I will try and bleed the system better. Not sure I understand the reaction that is causing basic pH. Oxygen(air) certainly leads to oxidation but not sure what causes pH 12-13? Thanks
High PH is corrosive as well. I know first hand, my hydronic loop had high PH, and I thought it was due to the iron filter system I was using. I had to have a flat plate heat exchanger replaced because of refrigerant leaking into water loop. I was adding soda ash to my well water to raise the PH, iron filter needed PH of 7.6- 8. I, like you discovered the radiant water to be 12-14 PH. I blame myself for raising it too high, your situation makes me wonder. I have no idea what would raise it like that. One geo guy said I should just add anti-freeze to my radiant water to stabilize the PH, don't know for sure if it would work. Sorry for your trouble, hope you can resolve it.
Is your system oxygen barrier pipe? I ask as, if it is, I'd go with a system clean and refilling with an appropriate solution. That could include antifreeze, inhibitors, etc. If it is not non-02 barrier pipe, then I would look more at an inline system (magnetic filters, pot feeder, glycol feeder, etc.).
Just a couple of loose thoughts. Corrosion on any circulating system must be controlled. In commercial we can have problems with 44 degree water (algae can grow in 44 degree water) or with warmer or hotter water. One of the things we add to our closed water loops are chemicals that are oxygen scavengers. (Chemicals that change oxygen into insert things that don't cause problems) IDEALLY YOU NEVER WANT ANY OXYGEN IN A CIRCULATING LOOP, ESPECIALLY CLOSED LOOPS. I just retired from commercial hvac. I don't like rust. It causes further problems. I used to have to deal with external water treatment of water towers used to cool our 900 ton centrifugal chillars. (Those are really "open" systems) Corrosion on closed systems is easier to handle. First, know what you have. Hire commercial testing, if necessary. I believe in flushing dirt until systems are clean ! (Beware of screen strainers ! All the trash collects there !) But once you identify a problem: too alkaline, too acidic, chemicals can adjust that so you become neutral and non reactive. Once acidity, for example, is under control, just take samples the next two years, to verify that nothing is changing ! Good Luck !
Hey Thanks for all the helpful replies. One very unusual thing about my radiant system is that the radiant tubing is rubber tubing. It is normally used with boiler based radiant retrofits. The bozo bullshit artist contractor that originally installed the radiant system thought he knew it all since he had installed boiler based systems before. He used the rubber tubing I think it is Black Onix, for the underfloor installation. I don't know if there is any oxygen barrier ability with this tubing at all. If not that could be a major oxygen source and would explain all the oxidation and rust. The system has a B&G pressure reducing valve at the water makeup supply ( I have it plumbed to the hot, softened, water) I was thinking of just connecting one of the spigots to drain ( or more likely many along the system at different times) and then opening the B&G valve and flushing the hell out of everything. I was then going to do a final fill with the Sentinel X-100 inhibitor. I have a Taco 4900 series bubble eliminator mounted above the expansion tank to remove all the air hopefully. The expansion tank will obviously be replaced as well. Does this sound like a good plan of action? Any suggestions for what else I can do?
=================================================================================== I am confused by your referance to rubber tubing. Rubber and other materials are commonly used around hot water insulation, cold water insulation, insulation of suction lines on hvac systems. I have never heard of rubber causing such problems. The problems that I just referenced, are explained something like this: corrosion often begins INTERNALLY. For example: a deteriorating hot water heater may give up iron or steel in particle form. If those particles circulate in hot or cold water pipes, wherever the particles settle or stick, THAT place will corrode and develop one or multiple pinhole leaks. Why ? Answer: because steel and copper are dissimilar metals. Dissimilar metals perform as batteries; (they produce electricity while consuming anode and cathode) Corrosion theoretically could also begin on the outside of copper pipes or inside depending on what it is exposed to: Imagine a marine environment. My experience both at my home and a Medical School was with INTERNAL corrosion on the inside of pipes. With clean, neutral water on the inside, copper can last a long time, (but doesn't always) I think others could help you more if you post some good photos of what you have so we can understand what you are seeing.
Hey, Again thanks for your reply. I'm at work now so I'll have to go get the exact info off the tubing when I get home. I'm pretty sure the tubing is similar to this: https://www.supplyhouse.com/Watts-086061-160-3-8-Onix-Tubing-160-ft-coil-8528000-p I'll check the part numbers on it to see about the oxygen barrier characteristics but its some version of the Onix. I fully understand that we are talking about internal corrosion. The expansion tanks have corroded from the inside out. Something is making the water caustic and strongly oxidizing hence the corrosion. I was thinking to flush it heavily and add corrosion inhibitor. Not sure what else I can do except for a drastic step like an in-line Ion-exchange tank. External corrosion is minimal and cosmetic only. I don't see any locations where galvanic corrosion can occur. Its all either plastic(PVC) , Rubber (Onix) or copper.
