Rapidly Dissolving Anode - Seeking Advise To Puzzling Problem

[MARK JAMES]

Hi everyone! I am seeking advise to a corrosion problem, I have a circulator design I am working on. This is a 40 to 115 degree closed loop “city water” circulator. The water reservoir is 304 stainless and has a115v-1500w immersion heater, threaded into the tank. There is an overtempt snap disc attached to the side of the sst tank with potting compound. The sst reservoir is sitting on an aluminum stand (screwed to the aluminum body of the entire outer case assy) above the pump and cooling lines running underneath it.

There are brass elbows and silicone rubber hose in the loop and water is pumped thru all by an Iwaki mag drive pump.

Initially, the heater elements were being eaten up /corroded and shorting out. I added a magnesium anode threaded into the top of the tank and now the anodes are being destroyed/dissolved rather quickly and the dissolved anode material is attaching itself to the heater element and blowing the snap disc.

This portable circulator is plugged into an external duplex box, attached to the back of another powered piece of equipment.

Question, could I have a grounding issue? Or is this a normal downside to dissolving magnesium anodes? Thanks in advance for any ideas!Mark

 

[anorlunda]

I added a magnesium anode threaded into the top of the tank and now the anodes are being destroyed/dissolved rather quickly and the dissolved anode material is attaching itself to the heater element and blowing the snap disc.

How quickly?

In marinas, wiring mistakes are not uncommon. The resulting galvanic corrosion can be devastating nearby boats.

There are instruments that you dip into the water to measure the galvanic potential. Galvanometer should be the correct word, but that word has come to be generic for meter movement actuator. Perhaps you can rent or borrow one, or find a used one on Ebay.

Here is a helpful bulletin from Fluke on how to do the job using a high quality multimeter.
http://assets.fluke.com/appnotes/electricalpower/B0269b_u.pdf

 

[MARK JAMES]

Within 3 months the anode (McMaster-Carr #3642K17) is completely dissolved. Thank you for the link!

 

[jim hardy]

just reminiscing here, maybe it'll wake up an idea...

Here is a helpful bulletin from Fluke on how to do the job using a high quality multimeter.
http://assets.fluke.com/appnotes/electricalpower/B0269b_u.pdf

We mapped those half cell readings around our power plant intake structures . We had active cathodic protection and used the half cell readings to set anode current.

I added a magnesium anode threaded into the top of the tank and now the anodes are being destroyed/dissolved rather quickly and the dissolved anode material is attaching itself to the heater element and blowing the snap disc.

Is that anode passive or powered ? If powered how did you set current to it ?

Are your heater elements stainless sheathed ? Boat guys know stainless steel and carbon steel and salt water don't mix.

old jim

 

[ChemAir]

Initially, the heater elements were being eaten up /corroded and shorting out. I added a magnesium anode threaded into the top of the tank and now the anodes are being destroyed/dissolved rather quickly and the dissolved anode material is attaching itself to the heater element and blowing the snap disc.

If the elements were shorting out due to galvanic or stray current corrosion, and you have added an anode, and that anode is now plating material at the heating element, I'd be suspicious of a voltage leak from the heating element to the water. I'd try and verify the power for the element is isolated and well grounded.

Another thought, with this much electrochemistry going on with "city water", you may need to remove (purge/blowdown) dissolved materials and change water to keep the conductivity lower.

 

[CWatters]

I might be misunderstanding American terms but... If a circulator is a closed loop heating system can't you dose it up with corrosion inhibitor? I guess the reference to city water means its not a closed loop.

 

[anorlunda]

The sacrificial anodes on my [EDIT boat] in Salt water lasted 1 month to three years depending on? I'm not sure why the variations. So 3 months doesn't sound bad to me. The anode should be checked every 30 days.

When there is a wiring error causing severe damage, I have seen results like in the picture in less than a week.

Or like this in a month

 

[Tom.G]

Are your heater elements stainless sheathed ?

Like that.
If not, get some that are.

You can also try mounting the existing heaters with an insulating bushing so they do not make electrical contact with the SS tank.

What heaters are you using, make, model?

EDIT: There are also companies that service boilers that have the knowledge, experience, and facilities to diagnose, fix, and maintain such systems. They may be the best bet for both an education and a solution to the problem.

Cheers,
Tom

 

[MARK JAMES]

just reminiscing here, maybe it'll wake up an idea...



We mapped those half cell readings around our power plant intake structures . We had active cathodic protection and used the half cell readings to set anode current.
Is that anode passive or powered ? If powered how did you set current to it ?

Are your heater elements stainless sheathed ? Boat guys know stainless steel and carbon steel and salt water don't mix.

old jim

Yes the anode is passive and yes the heater is sheathed stainless. And we are using regular old tap water in the system. Mark

 

[MARK JAMES]

I might be misunderstanding American terms but... If a circulator is a closed loop heating system can't you dose it up with corrosion inhibitor? I guess the reference to city water means its not a closed loop.

By closed loop I mean that the water flowing through the heating/cooling hoses is self contained and must be refreshed manually. Just like a cars radiator. Also these exit the circulator and travel thru a larger external tank containing plating chemicals.

 

[MARK JAMES]

Like that.
If not, get some that are.

You can also try mounting the existing heaters with an insulating bushing so they do not make electrical contact with the SS tank.

What heaters are you using, make, model?

EDIT: There are also companies that service boilers that have the knowledge, experience, and facilities to diagnose, fix, and maintain such systems. They may be the best bet for both an education and a solution to the problem.

Cheers,
Tom

I wondered about a bushing, we are currently using teflon tape though. The heater is McMaster Carr # 3656K153, TEMPCO # TSP02245. Thanks!

 

[MARK JAMES]

If the elements were shorting out due to galvanic or stray current corrosion, and you have added an anode, and that anode is now plating material at the heating element, I'd be suspicious of a voltage leak from the heating element to the water. I'd try and verify the power for the element is isolated and well grounded.

Another thought, with this much electrochemistry going on with "city water", you may need to remove (purge/blowdown) dissolved materials and change water to keep the conductivity lower.

Great information and a confirmation on a thought we had earlier. I will on a purge immediately. The voltage leak I will have to get some help with. Thanks

 

[MARK JAMES]

Like that.

EDIT: There are also companies that service boilers that have the knowledge, experience, and facilities to diagnose, fix, and maintain such systems. They may be the best bet for both an education and a solution to the problem.

Cheers,
Tom

 

[MARK JAMES]

In the end, this just might be the path taken. But so far, everyone is helping a bunch with great ideas and confirmations to some of our thoughts as well.

 

[Svein]

I have some experience with such problems. My father-in-law produced water heaters and he had problems with the heaters corroding in some types of water. Some research showed that:

• There was a temperature difference between the immersion heater and the water around the heater
• This temperature difference had a linear dependence on the power dissipated in the immersion heater
• For a power dissipation of 2kW, the temperature difference was about 22°C
• Thus, if the heater thermostat was set to 85°C, the immersion heater would often be at or above 100°C.
• Since 100°C is above the boiling point of water, the water in contact with the immersion heater would boil
• Boiling water in contact with the immersion heater would create calcium deposits in "hard" water
  
• Calcium deposits on the immersion heater tends to create a high thermic resistance between the immersion heater and the water, increasing the temperature inside the immersion heater to increase beyond spec - and the immersion heater would crack
• A cure for those problems was to go with an electronic thermostat that reduced the power at high water temperatures, keeping the immersion heater temperature below 100°C.

 

[jim hardy]

A cure for those problems was to go with an electronic thermostat that reduced the power at high water temperatures, keeping the immersion heater temperature below 100°C.

We have that same problem here in the Ozarks with our water heaters . The ground is mostly limestone so well water has a lot of calcium in it , the water heater elements get coated and burn out way too often.
If i could stand the slow recovery i'd rewire mine to 115 volts.

Hmmmm... might this simple experiment be worthwhile ?

The heater is McMaster Carr # 3656K153, TEMPCO # TSP02245. Thanks!

https://www.tempco.com/Tempco/Resources/11-Process-Resources/ScrewPlugHtrCatalogPages.pdf

^^ your heater ^^

if you can stand the extra immersion length , this one has 37 vs 94 watts / in^2

 

[CWatters]

By closed loop I mean that the water flowing through the heating/cooling hoses is self contained and must be refreshed manually. Just like a cars radiator. Also these exit the circulator and travel thru a larger external tank containing plating chemicals.

Just to be sure... So the contents is not being continually replaced with new water (only during maintenance) and it doesn't mix with the plating chemicals it heats them via a heat exchanger?

In which case it's similar to my home heating system which I dose up with Fernox F1 to prevent corrosion. Perhaps a similar chemical process can be used in yours?

Is it possible the plating chemicals are leaking into the heating loop and causing the problem?

 

[MARK JAMES]

Just to be sure... So the contents is not being continually replaced with new water (only during maintenance) and it doesn't mix with the plating chemicals it heats them via a heat exchanger?

In which case it's similar to my home heating system which I dose up with Fernox F1 to prevent corrosion. Perhaps a similar chemical process can be used in yours?

Is it possible the plating chemicals are leaking into the heating loop and causing the problem?

The stainless steel tank/reservoir has a fillport on top and is filled with water manually. Corrugated teflon PFA tubing is used to flow the heated/cooled water thru the interior of the chemical tank and return it to the reservoir. Same principal as a cars heater core except the teflon tubing acts as the heat/cool exchanger. Only if the teflon tubing fails will the plating chemical leak into the water in this circulation loop. So far that has not happened, but good question!

 

[jim hardy]

Only if the teflon tubing fails will the plating chemical leak into the water in this circulation loop. So far that has not happened, but good question!

The stainless steel tank/reservoir has a fillport on top and is filled with water manually.

When troubleshooting ya' always got to quietly check the dumb stuff. If it doesn't pan out you just don't admit you were dumb enough to even look.

But having no idea what your installation looks like, i just have to ask How far apart are those fill ports for the water reservoir and the plating tank ? How are they marked?
Could a non technical person mistakenly pour plating solution into the wrong one?
Stand back and see if your entry level guy could possibly make that mistake.

Color coding and bold unambigous signage are key.

sorry if it's a way off base suggestion.

old jim

 

[MARK JAMES]

When troubleshooting ya' always got to quietly check the dumb stuff. If it doesn't pan out you just don't admit you were dumb enough to even look.

But having no idea what your installation looks like, i just have to askHow far apart are those fill ports for the water reservoir and the plating tank ? How are they marked?
Could a non technical person mistakenly pour plating solution into the wrong one?
Stand back and see if your entry level guy could possibly make that mistake.

Color coding and bold unambigous signage are key.

sorry if it's a way off base suggestion.

old jim

Very true!

The fillport for this circulator is behind a wall (fab clean-room chase way) and the fillport for the chem tank is in the cleanroom itself. The chase way is only occupied by maintenance members. Since this anode/heater is continual problem and not an accidental cross contamination issue, I'm completely confident we can rule that out. I did however verify, just to be sure! Thanks

 

[jim hardy]

I did however verify, just to be sure!

No one else ever need know. .

 

[MARK JAMES]

Lol

 

[MARK JAMES]

To All, we are currently evaluating the whole assembly and testing the ideas presented here. I will report back on what we find out as soon as I can. Thanks again to everyone for the help!

Mark

 

[dlgoff]

Sounds to me like the problem is with the water. I was involved with temperature and humidity controlled environmental chambers for the pharmaceutical industry. The humidity levels were maintained by injecting steam into the temperature controlled air stream. The steam generator tanks would get eaten up by just using "city water" so I installed deionization resin tanks to supply these steam generators.

image compliments of http://www.waterspecialties.net

 

[Tom.G]

The steam generator tanks would get eaten up by just using "city water" so I installed deionization resin tanks to supply these steam generators.

This and the post by @Svein (https://www.physicsforums.com/threa...vise-to-puzzling-problem.964728/#post-6122723) point to the same thing, essentially mineral water being boiled at the heater element surface.

Additionally, the periodic addition of makeup water was mentioned. That indicates a loss of water, probably thru evaporation. That will evaporate the water but leave the minerals behind in an ever-increasing concentration. Oops! Closed system anyone?

Cheers,
Tom

 

[jim hardy]

That will evaporate the water but leave the minerals behind in an ever-increasing concentration. Oops! Closed system anyone?

or use distilled water , maybe even catch rainwater, for that side of the cycle.

 

[MARK JAMES]

Just a little update, currently Di water is used in the system and as we know the minute Di water touches all that stainless steel it grabs the elements it needs to return to normal ionized water. Our Di system is multi staged filtered as well.

More and more the "Element Watt Density" is looking like our strongest problem contributor. The stainless steel tank was the limiting factor for heater element size and we are looking at the 2" longer element in a tank redesign at this time. I will report back of course.