Revision: Water Heaters and Corrosion of Anode Rod

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    • #276725
      MasterPlumbers
      Keymaster

      I am investigating a water heater that corrode and caused damage to a residence. When we opened up the unit the anode rod was gone. This was understandable because the water in the area was very hard. However, is it possible that a water heater without a functioning anode rod would subsequently leak/rupture?

    • #294668
      nicktheplumber
      Participant

      The anode rod in a water heater is made of magnesium or aluminum. It is called an “anode”because it is at positive electrochemical potential in an electrolytic “cell.” The purpose of this rod is “sacrificial,” i.e. it corrodes away and thus spares the walls of the tank (made usually oif some ferrous material at a lower redox potential than iron), from corrosion. All water heaters should have a sacrificial anaode. They are especially needed in systems that have water “softeners,” as these tend to oproduce conditions that lead to electrolysis of ferrous tank walls. The lack of a sacrificial anode, especially in a system with a water softener, can lead to a rotted water heater tank.

      NtP

    • #294669
      GarySlusser
      Participant

      I know that some water heater manufacturers blame their tank failures on water softeners but… they never show the chemistry to back up their claims.

      They also tout their glass lining. Glass is impervious to anything found in water, so howzit that water with the hardness removed and a bit of sodium added (about 7.85 mg/l per grain per gallon softened), causes their glass lined tanks to rust out?

      So if anyone knows the chemistry of the claim, I’d like to see it. For all the millions of softeners in use in both residential and commercial establishments, it certainly would be announced to everyone if those softeners were responsible for ruining water heaters. And if the glass lining remained intact, you could fill the heater with acid or alkaline and it wouldn’t rust out; anode rod or not.

      Gary
      Quality Water Associates

    • #294670
      nicktheplumber
      Participant

      Gary makes a good point about the “glass” lining of some water heaters. I suspect that the corrosion leaks seen in such tanks (and they do corrode and leak) is due to the fact that the inlet and outlet connections to the tanks is made of ferrous metal. Unless the WHOLE cold water supply and hot water distribution system is lined with an inert material, there will be points where water is in contact with metal. As regards the tank, these points are at the inlet, outlet, and overflow connections. These parts are subject to electrolytic corrosion and leakage. the corrosion at a connection can also extend to the OUTSIDE of the ferrous tank. For this reason, sacrificial anode rods are a good idea in any tank connected to a metallic pipe system…

      NtP

    • #294671
      Selgas
      Participant

      Can’t speak for thest of you folk but down here in the area my Comapny works in we have “Hard Water” and find that especially in gas fired water heaters that the life expectancy is around 8 to 10 years max. Those fitted with water softeners last approximately 10 to 15 years.
      We have found on the hundreds that we have removed and replaced due to leakages that once the anode has corroded (been consumed) any flaw whatsoever on the enamel glass lining readily turns into a rust spot and from there a leak develops.
      We have found that when transporting these water heaters many have had the anode break off and fall into the tank due to heavy and harsh handling – either from the delivery Companies or the Installers banging them about. This then leads to a very fast breakdown and the resulting leakage.
      We have not yet (after 35 years of this kind of work) found one that had been used on a water softener to have failed earlier than one that has not been connected to one.
      Tiss just a fact of life the manufacturers expect failures of glass lined cylinders and have down here at least given them a life expectancy of 10 to 15 years use in domestic dwellings with or without water softeners.



      Selgas Services Ltd
      Craftsman Gasfitters, Plumbers, Electrical Service Technicians

    • #294672
      Robert Stephen Morton
      Participant

      Nick & Garry, The glass lining is applied by a probe inserted into the tank & then th nozzle on the end sprays a vitreous enamel indide the tank, the tank is then fired & thus the glass lining, it is in fact similar to the lining of a vitreous enameled panekin used by millions of workers for their morning coffee or tea.
      with fluctuations of pressure within a hot water service the lining gets crazy cracked & hence the need for the anode ( to protect the minute areas exposed by the cracking.
      The Anode is the reason that HWS should never be transported on their side, because with the whipping of the anode will chip the enamel and or the anode will snap off at the plug, rendering the anode useless & the HWS with no warranty.
      Bob

    • #294673
      nicktheplumber
      Participant

      Robert,

      Thanks. I didn’t know those details of the “glass lining.” It makes a lot of sense, especially as regards the crazing cracks, and explains why the anode rods are still needed.

      NtP


      In reply to message posted by Robert Stephen Morton:
      Nick & Garry, The glass lining is applied by a probe inserted into the tank & then th nozzle on the end sprays a vitreous enamel indide the tank, the tank is then fired & thus the glass lining, it is in fact similar to the lining of a vitreous enameled panekin used by millions of workers for their morning coffee or tea.
      with fluctuations of pressure within a hot water service the lining gets crazy cracked & hence the need for the anode ( to protect the minute areas exposed by the cracking.
      The Anode is the reason that HWS should never be transported on their side, because with the whipping of the anode will chip the enamel and or the anode will snap off at the plug, rendering the anode useless & the HWS with no warranty.
      Bob


    • #294674
      Bruce T
      Participant

      Doesnt a water softner in action “remove” calcium and MAGNESIUM and in doing so attack the magnesium sacrificial anodes?
      water heaters with softners have a very high rate of anode breakdown.
      I asked a rep from a softner company about this and he said they actually recommend removing the anodes!
      Voiding warranty of course!
      Its all very confusing.

    • #294675
      GarySlusser
      Participant

      Previously I failed to mention that hardness has nothing to do with the anode rod being used up, or deteriorating.

      Ion exchange water softeners work by attracting + charged ions in the water to the negative charged sites on the resin ‘beads’. The process is called ion exchange because the exchange is roughly two sodium, or potassium, ions for each ion removed. Ions removed are iron, calcium, magnesium, lead, copper, radium etc. and are much larger than the sodium or potassium ions the resin is regenerated with. The ions removed are soluable, meaning they are dissolved into the water. Softened water does not attack metals. Neither does sodium that is added in the process. Sodium or potassium comes from sodium and potassium chloride; water softener ‘salt’. The chloride part is not used and is flushed to drain. Chloride is corrosive to most metals; especially stainless steel.

      Confusion exists due to softened water being confused with naturally soft water. Naturally soft water is water with little hardness but a lot of DO and CO2 content with little TDS and a low (acidic) pH. That water is aggressive and eats metals.

      Other than stray elcetrical current, the biggest cause of anode rod deterioration is bacteria. The bacteria is primarily sulfate reducing bacteria (iron and manganese are others) and they thrive in low temp (<140f) water heaters and use the anode rod as a food source. In many cases this will ad a 'sulfur' odor to the hot water. Anod rods that are larger than normal with a softish fluffiness are under attack by bacteria. In most cases the water source will be a private well. City water that is properly chlorinated won't/shouldn't have bacteria of any kind in it. So maybe the tech wasn't diferentiating between the two sources of water. But if you have the opportunity, ask for the chemistry to prove his claim.

      Here’s a goggle search for “sulfate reducing bacteria”, it provides very indepth information about it and the problems it causes. (copy and paste)

      http://tinyurl.com/g19c

      Here are two URLs that have a large amount of info on corrosion:
      http://www.hghouston.com/TFAQ.html

      At the bottom of this page, click on the click here to read what experts say about indices.

      http//www.corrosion-doctors.org/NaturalWaters/Frames.htm

      Gary
      Quality Water Associates

    • #294676
      Bruce T
      Participant

      Wow! Outstanding Info Gary!
      Thank you!
      I am printing it out for reference!

      I have however seen a brand new (less than one year old) commercial electric water heater tank failure using CITY water with a sodium water softner that had BOTH anodes completly gone! nothing left but the wire.
      can this be from improper maintenance or regeneration of the sodium softner?
      The water heater was replaced by the manufacturer (6 year commercial tank warranty).
      Or could there be other causes for rapid anode deterioration such as a flaw in the glass lining?
      Thanks!

    • #294677
      Bruce T
      Participant

      This came from A.O. Smiths website…the 1 year old heater I speak of was in fact an A. O. Smith heater with dual anodes.

      Bulletin #44:TECHNICAL BULLETIN 44
      WATER SOFTENERS
      GENERAL The use of water softeners in hard water areas and even moderately soft water areas is becoming a common occurrence. This practice has a potentially detrimental effect on the performance of the anode in the water heater which can cause a reduction in the life of the water heater. Scale caused by hard water can result in clogged pipes and reduce a water heater’s recovery efficiency. Washing, bathing, and shampooing in hard water leaves a film and solid particles on the skin. The problems are caused by insoluble cations in the water. The predominant cations in water are calcium and magnesium. Water softeners work by exchanging soluble sodium ions for the insoluble calcium and magnesium ions. This process is called ion exchange and is performed by a substance called zeolite. The zeolite is precharged with sodium ions which attract the calcium and magnesium ions and exchanges them with sodium. Periodically, the softener is recharged with sodium by running salt (sodium chloride) through the zeolite resin bed.
      EFFECTS · Sodium reduces the hardness of the water, but it does not reduce the conductivity of the water. Excessive conductivity in the water will accelerate anode decomposition resulting in more rapid anode consumption.

      · If the resin bed of the softener is not properly rinsed after regenerating the resin, residual salt will get into the heater. This will increase the conductivity of the water and result in more rapid anode consumption.

      · Water softeners accelerate anode consumption because they eliminate the formation of scale in the water heater tank. Light scale formation in a water heater is desirable since it forms a barrier film on the exposed steel surfaces in the tank, such as pipe connections and weld areas. Corrosion cell tests at the Corporate Technology Center have shown steel corrosion rate drop of 33% with the formation of a thin (<1/16”) film of scale after only three weeks in moderate conductivity water (17 grains hardness). By allowing a thin layer of scale to form on the tank, the steel would be protected, therefore, increasing the life of the anode.

      NOTE Customers using water softeners should expect more rapid anode consumption. Anodes should be inspected more often and replaced when nearing the end of their useful life.
      ____________________
      Is this useful information to pass on to my customers or is it B.S. Gary?
      It kind of makes sense as far as anode protection by light scale on the side walls, but wouldnt that make the efficiency of the water heater less and create more problems by hot spots and such? (expansion and contraction?)
      This is the only water heater site that I have seen that deals with this issue. But I personally dont recommend this brand of heater due to problems I have had in the past with customer service.
      Thanks in advance.

    • #294678
      GarySlusser
      Participant

      Bruce, that bulletin is what I was refering to earlier when I said heater manufacturers blame softeners.

      Yes it would be very useful to your customers and you should tell your customers but only if it were true, which it isn’t. And after this you may have something else to tell them that actually saves them money. That would be to soften their hard water.

      Points in smith’s brief: To my knowledge Zeolite is only made by one company in North America and it is used for water softening very little today compared to many companies making synthetic (plastic) resins.

      Softening only slightly increases a water’s TDS and/or conductivity levels. Sodium is added to the water as I said before, at roughly 7.85 mg/l per grain of ‘hardness’ removed. That’s a very small amount and if average exhange were say 10 gpg, the TDS increase would hardly be measurable.

      Insoluble cations! Ion exchange only removes soluble cations or anions, I don’t know what they’re talking about using the word insoluble; that’s a particle. Softeners aren’t filters unless we talk about chunks!

      “Sodium reduces the hardness of the water” Actually ion exchange water softening removes the cations like a magnet picks up iron filings from a file. Sodium or potassium is exchanged for the cations removed but isn’t responsible for removing the cations.

      “Excessive conductivity in the water will accelerate anode decomposition resulting in more rapid anode consumption.” Excessive! The water is already conductive and increasing conductivity by what, 2% is going to ruin their anode! I’ll bet millions of water heaters have the anode rod gone for many years and the water in them has been softened.

      And then they say “Water softeners accelerate anode consumption because they eliminate the formation of scale in the water heater tank.” Amazing! They want scale formation to protect their tank and then go on to talk about an uncontrolled amount but like 1/16th inch! As if they don’t know scale builds and continues to build as long as hardness is in the water and heat is applied to it! Note in 3 weeks they had a 1/16th inch! That costs their customer a lot more money on fuel costs than replacing their water heater in years! And as I said, if their glas lining was intact and correctly applied to their low grade steel tanks they wouldn’t have the problem; or desire a backup protection plan. I’ve read a study that says for each 1/16″ of scale you waste about 30% of each dollar it costs you to heat water in a water heater. And yes, hot spots in gas and oil fired heaters are the cause of failure and in electric heaters, many times the scale falls off the elements and fills up the bottom of the tank displacing water and increases the recovery time.

      “formation of a thin (<1/16”) film of scale after only three weeks in moderate conductivity water (17 grains hardness). By allowing a thin layer of scale to form on the tank, the steel would be protected, therefore, increasing the life of the anode."

      First, you don’t measure conductivity by the amount of hardness in the water; it is all of the solubles that make up the TDS (total dissolved solids) in the water and you use a conductivity meter. That includes the alkalinity, iron, manganese, copper, lead, hardness, chlorides, sulfates, H2S, VOCs and on and on. Remove the hardness and the TDS stays the same or slightly increases dependent on the amount of ion exhange being done. In other words the water is aggressive or it isn’t before it’s softened.

      They are throwing words around but really don’t know what they are talking about. We should ask them why huge commercial water softeners using say ten foot diameter and 20′ tall steel tanks don’t have anode rods…

      Here’s a site I just found that explains ion exchange quite well. It deals mostly with anion resins in the hydrogen form and dionized water but mentions sodium form strong acid cation resins which is the resin in ion exchange water softeners.

      http://www.remco.com/ix.htm

      Gary
      Quality Water Associates

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