Heat Exchanger/chemistry

[paddow]

hi, i have a starite heater that is just finishing its second season,when i discovered water coming out of it. i took the covers off and i found water coming out of the blower. my pool is about 41000 gallons. i have a salt water generator. my chemistry is chl 2 -3ppm my cal is around 150, my ph is constantly at 7.4 to 8.2 my alk is usually 70 to 90. i usually add 3/4 gal to 1 gal per week . and i always pour it in the deep end away from the returns or the skimmers.the pool looks fine but i do have some calcium build up on the gout joints on the tiles.i called starite techs and they told me my chemistry is off.that i probably have corrosion on my heat exchanger. the man said that it is impossable for ph to be 7.8 or 8.0 if my alk is 80ppm. he also told me that ph and alk are the same things. this water has never had a low ph if anything it is consistently high. i've tried several test kits and the ph reading and the alk reading is always on the high end of things. i guess my question is how could my heat exchanger corrode with a higher than normal ph. is it possable to have a low alk ( 60 -80ppm) with a high ph (7.8-8.2)by the way i have weekly records that i keep with the chemistry readings and i have never had a low ph reading

[Pool Clown]

If you are putting too much water thru the heater (gpm) you can actually erode away the copper exchanger in the heater.

[quantumchromodynamics]

Failure after two years indicates a problem somewhere. We will need more information to figure out what is causing the leak.

01) What is the horsepower of the pump?

02) What is the "Service factor" of the pump? (Listed as S.F on the motor label).

03) What is your normal filter pressure?

04) Is the heater before or after the chlorine generating cell?

05) What chemicals have you ever put in your skimmer?

06) What is the flow rate through the heater?

07) What are the make and model of your pump, filter, heater and chlorine generator?

09) Have you ever had a trichlor feeder?

10) Have you ever put trichlor tabs in your skimmer basket?

Can you take out the heat exchanger and look into the copper tubes? What does the copper look like? What does the outside of the copper tubes look like? Can you see a hole or holes? Where are they and how big are they?

Can you get a DC voltage reading from the heater to the bond wire? Negative lead to the bond wire, positive lead to the heater. Note if the reading is positive or negative.

[chem geek]

i called starite techs and they told me my chemistry is off.that i probably have corrosion on my heat exchanger. the man said that it is impossable for ph to be 7.8 or 8.0 if my alk is 80ppm. he also told me that ph and alk are the same things.

is it possable to have a low alk ( 60 -80ppm) with a high ph (7.8-8.2)by the way i have weekly records that i keep with the chemistry readings and i have never had a low ph reading

The starite techs don't know what they are talking about. pH and Total Alkalinity (TA) are NOT the same thing. You can absolutely have a low TA with a high pH. They are probably thinking only about pools that use only Trichlor as their source of chlorine and in such pools the pH is usually low if the TA isn't high because Trichlor is very acidic.

It is unlikely your heater corroded from pool water chemistry unless the pH was low at some point such as having Trichlor pucks in the skimmer or pouring acid into the skimmer. If your pool has very high TDS levels, then the extra conductivity can accelerate corrosion so this is probably your situation as you have an SWG. As others have noted, if the flow rate is very high then that can accelerate corrosion as well.

Was the corrosion in the heater from the inside or the outside? Some heater corrosion can occur from the outside if there are cycles of usage at lower air temperatures where condensation can occur.

You didn't mention your Cyanuric Acid (CYA) level. If it's zero (unlikely if this is an outdoor pool) then the chlorine will be far too strong, especially for corrosion with the higher salt levels.

As was noted in the previous post, see if your heater is properly bonded or measure the voltage between the heater and the bonding wire.

Also, I assume that your SWG was placed AFTER the heater and not before.

[quantumchromodynamics]

Excessive flow rate through the heater, as noted by P.C, would be the most likely based on the size of the pool.

At 41,000 gallons, the pump is probably about 2.0 to 2.5 H.P. Many inexperienced pool builders will send the entire flow rate through the heater. It's important to limit the flow rate through the heater. I keep the flow rate near the lower end of the recommended range.

I think that it's important to note that excessive flow rate causes mechanical erosion (As P.C noted) and not chemical corrosion. The metal will be stripped away without being oxidized. It's similar to using sandpaper. It's a mechanical destruction instead of a chemical one. Of course, chemical oxidation will also occur and the two will act synergistically to cause rapid destruction.

A few more questions:

11) Are there any metal stains, especially green stains, anywhere? If yes, please describe.

12) Is there any corrosion on anything else? Lights, handrails, ladders etc.

13) Does the entire flow rate go through the heater or is the flow controlled in some way?

14) How many times have you cleaned your cell?

15) What did the scale look like in the cell? What color was it?

16) Has anyone complained about any types of minor shocks when in the pool or when getting in or out of the pool?

17) Is the pool vinyl liner, concrete, tile or fiberglass?