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Thread: Copper and Chlorine

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    Copper and Chlorine

    Boy did I mess this up! in trying to delete the multiple posts, I managed to delete the whole thread! So Sorry!

    Here it is:

    Quote Originally Posted by gregs

    Sat Sep 08, 2007 11:50 am

    I am looking for some info regarding chlorine levels and there effects on copper piping. I am going to install a fiberglass pool this fall with a swg. One thing I am considering is to tye my homes geothermal heat pump system into the pools pump/filter circuit to use it like a heat pump pool heater. Currently it is set-up as an open loop system connected to my well and just returns the water back out into the woods. I would plumb it in so that I could go between the pool and the well system if the pool is getting to hot. My concern is with the effect of the chlorine levels on the copper piping and heat exchanger. I have been told that you can run the FC levels very low with a fiberglass pool. How low can the levels be and still perform correctly? I have contacted the Copper Pipe Association to see if the have a maximum ppm level for standard copper piping. I will probably post this in a different spot as well, so if the admistrator wants to take it out and move it to a better location thats fine. Thanks

    Quote Originally Posted by JasonLion

    Sat Sep 08, 2007 12:12 pm

    The available information is somewhat limited, as salt corrosion is normally reported at very low salt levels as compared to sea water, while a typical SWG uses levels in between those two.

    The best I have been able to figure out is that copper is fine at salt levels below something around 6000 ppm, although salt can somewhat aggravate corrosion from other sources. Copper-nickel alloys are generally fine even at sea water levels of salt.

    Many of us have heaters with copper heat exchangers and 2500-4000 ppm of salt in our pools and don't experience any obvious problems.

    Low PH is a far more serious problem for copper piping. If the PH falls enough below 7.0 there can be significant and fairly rapid damage to copper pipes.


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  2. Back To Top    #2

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    I agree with Jason. The corrosion of copper is probably somewhat linearly proportional to the salt level (actually, the conductivity of the water) as well as oxidizer level (actual disinfecting chlorine, not Free Chlorine), but the pH is the biggest factor by far and is not linear (pH isn't a linear scale; it's logarithmic). So under normal conditions with pools that use Cyanuric Acid (CYA) and keep their pH in a normal range well above 7.0 almost all the time, then the copper piping shouldn't corrode.

    Remember also that municipal water districts used to (some still do) use chlorine without CYA in their water systems at levels of around 1-2 ppm FC, though the pH was usually closer to 8.0. Even so, that's a far higher disinfecting chlorine concentration, albeit with very low salt levels, and corrosion in copper pipes wasn't something you heard about. Now, many water districts use monochloamine instead (at around 1 ppm FC), mostly to reduce disinfection by-products and because it lasts as a residual longer.

    Based on my discussions with a few PBs in my area, in gas heaters with copper heat exchangers, it seems that a lot of the corrosion, if not from low pH, comes from cycling and using the heater during colder partially humid weather. This causes a cycle of condensation inside the heater and the exposure of the copper to this water and oxygen in the air causes it to corrode. Think of copper objects left outdoors exposed to weather (rain, moisture and oxygen in the air). It will begin to darken and corrode, often turning green from copper oxide. The additional stresses of high heat (from the gas heater) crack and partially remove this oxide layer so instead of protecting the copper from further corrosion, the cycling continues to corrode the copper.

    They said they saw the corrosion problem more frequently in pools where the gas heater wasn't on frequently. That is, if the heater kept the pool water warmer -- above 70F or so -- at all times, then there were fewer problems. If the pool was cycled in heating and then cooled to 65 or below and then was reheated, then they saw more problems. Perhaps the warmer pool water produces less condensation on the pipe.

    The difference between the two types of corrosion is obvious as corrosion from bad water chemistry is seen coming from the inside of the pipe while the corrosion coming from the cold weather cycling condensation is seen coming from the outside of the pipe.

    Visible inspection of both inside and outside of the pipe is necessary to see if corrosion is occurring.

    Corrosion of stainless steel (and aluminum), on the other hand, operates quite differently since in this case chlorides in the water interfere with the "self-healing" of these metals so at certain salt and oxidizer levels the corrosion process becomes quite rapid (i.e. it's non-linear).

    Richard
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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    Someone from the Copper Association replied back telling me that the salt water would not be a problem with copper at those levels. The chlorine levels could be. This is what he wrote:

    "Chlorine in the levels found in potable water supplies in the US for disinfection purposes should not pose a problem with copper piping. The more than 70 years of use of copper in these systems in the US should testify to that fact. However, the inappropriate application of extremely high concentrations of chlorine can lead to accelerated copper corrosion (i.e. temporary disinfection or shocking the system with high chlorine levels for extended periods of time).
    Actually, tests have shown that chlorine in the levels found in water systems (usually 1 - 2 mg/L residual free chlorine) can be beneficial in that they promote the formation of adherent copper oxides that make the copper tube more corrosion resistant.
    As for pH levels a good range is 6.5 to 8.4.
    Low levels of CO2 are also important."

    So does anybody know how to convert mg/L to ppm? Or have an idea of what a minimum level of chlroine I can expect to get by with? If I monitor and adjust the PH, and the salt levels stay below 6000 then it looks like my chlorine levels would be the only thing to be concerned with. I just want to make sure that I dont cause leaks inside my house years down the road. Also if anybody has questions I should ask the guy from the Copper Association, let me know.
    Michiele
    Newbie pool owner
    25,000 gallon inground, vinyl lined pool, sand filter

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    JasonLion's Avatar
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    mg/L and ppm are the same. mg/L is the metric version and ppm is used in America. They are both parts per million. 1 L of water is 1,000 grams and a mg is 1/1,000th of a gram.

    Also, you can have far higher chlorine levels as long as you have CYA in the water and still be within the guidelines he stated. The CYA "deactivates" much of the chlorine, making the effective concentration much lower.

    Finally, I wonder about where he said "Low levels of CO2 are also important." Pool water generally has more CO2 compared to tap water. So just what "low" means will matter.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    This link from the EPA contains some useful info on copper corrosion such as the following:

    [hr]Pitting corrosion occurred only in low dissolved inorganic carbon (DIC) (5 and 10 mg C/L) and high-pH (9) water in the presence of chloride (20 mg/L) and was not observed at pH 7 or 8. Sulfate was not necessary to develop pitting corrosion; however, it did affect the composition of the corrosion by-products associated with pitting corrosion. Increasing the DIC from 10 to 50 mg C/L or adding 3 mg PO4/L prevented pitting corrosion at pH 9. A conceptual model was established that attributed pit initiation to the deposition of copper chloride or sulfate compounds on the pipe at the anode.[hr]

    The low dissolved inorganic carbon (DIC) of 5 and 10 mg C/L is equivalent to a carbonate alkalinity at a pH of 7.5 of 20 and 40. Note that the high pH of 9 with chloride of 20 mg/L (ppm) is a very low amount of chloride. Most non-SWG pools start out with around 350 ppm chloride and SWG pools have around 3000 ppm chloride. No pitting corrosion was observed at pH 7 or 8, but they didn't talk about any oxidizers such as chlorine being in the water supply.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
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    I will see if I can get a range for the CO2 amount.

    In the EPA quote it listed "PO4/L", do you know what that is?

    I am very new to the pool chemistry aspects. I understand that you use the cya to keep the chlorine from "breaking down" and becoming ineffective, is this what would be "buffering" it so as not to attack the copper? If thats true, then is it the "free chlorine" levels that I would need to be most concerned with? I was hoping that having a fiberglass pool would allow me to run lower levels of chlorine and the swg would be the best way to treat the water with chlorine and maintain lower levels. It will be a new pool this fall with very little shade and no screened enclosure.I will be starting at the begining with the water, so what chlorine levels would I be trying to maintain and test for? And I have also thought of adding some type of fountain to possibly aid in the cooling of the water, probably one of the floaters you plug into a return. Thanks for the help!
    Michiele
    Newbie pool owner
    25,000 gallon inground, vinyl lined pool, sand filter

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    The PO4 is phosphate (orthophosphate), but that is a nutrient for algae so we don't want to intentionally add that to pool water. So the EPA document is saying that 3 mg/liter which is 3 ppm or 3000 ppb of phosphate helps to prevent pitting corrosion at a pH of 9 -- but remember that they saw no pitting corrosion at a pH of 7 or 8.

    Cyanuric Acid (CYA) protects chlorine from breakdown from sunlight in two ways (we now believe). One way is as you describe it which is that the CYA absorbs UV light from the sun thus shielding chlorine at lower depths. However, this only seems to be a dominant factor when the CYA level is higher -- starting to become significant somewhere in the 40-60 ppm range. The other way CYA protects chlorine and is the main factor is that CYA and chlorine (specifically hypochlorous acid) combine to form new chemical compounds called chlorinated isocyanurates. These compounds are not effective sanitizers or oxidizers, but they breakdown from sunlight much more slowly than chlorine alone. The vast majority of the chlorine in the pool (at FC levels of around 11.5% of CYA level) -- about 97% -- is attached to CYA as chlorinated isocyanurates. Only about 3% is in the form of hypochlorous acid and hypochlorite ion split about 50/50 at a pH of 7.5. Only the hypochlorous acid is the effective disinfectant. Fortunately, it takes a very small amount of disinfecting chlorine to kill bacteria and to kill or prevent algae. So yes, when it was described that CYA buffers chlorine, it is holding chlorine in reserve, but in a form that does not attack copper pipes.

    So essentially with pool water that has CYA in it, you don't need to worry about the chlorine levels being so high as to attack metals (assuming pH is OK). The 1 ppm FC with no CYA that is still found in some municipal water districts is about 10 times higher than the normal amount of chlorine in a pool of 3.5 ppm FC with 30 ppm CYA (which is equivalent to around 0.1 ppm FC with no CYA). With an SWG, you will probably be running with even lower chlorine of around 3.1 ppm FC at 70 ppm CYA which is equivalent to only 0.04 ppm FC with no CYA.

    The Free Chlorine (FC) measurement from test kits measures the combination of disinfecting chlorine (hypochlorous acid), hypochlorite ion, and all chlorine in the chorinated isocyanurates. So it is not a true measure of the disinfecting or oxidizing power in the pool. This is why you need to look at both the FC and CYA levels to know if you've got enough disinfecting chlorine in your pool.

    The fountain will not only cool the pool, but will aerate the water and that may make the pH rise. The extra evaporation may increase the amount of fill water that gets added to the pool and that will increase some pool water chemistry values depending on what is in the fill water -- usually Calcium Hardness (CH) and Total Alkalinity (TA) -- though the aeration may effectively lower TA over time if you add acid to compensate for the rise in pH.

    Richard
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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    It sounds like I should be o.k. with a SWG for my chlorine as long as I maintain the CYA level and monitor and adjust for the PH. As far as the refilling of the pool from evaporation would it be better to use plain well water or softened water? My water doesnt have any other problems other than hardness.I think I remember the tests showing 16 grains of hardness and it had a trace amount of iron but nothing that required any additional treatment for. I had also considered filling the pool with treated water but I dont know if there would be much to be gained.
    Michiele
    Newbie pool owner
    25,000 gallon inground, vinyl lined pool, sand filter

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