Why Sacrificial Anodes?
There is a way of diverting the attention of the corrosive forces of water. It’s a process called Galvanic Corrosion. The technical definition is:
Galvanic corrosion is an electrochemical action of two dissimilar metals in the presence of an electrolyte and an electron conductive path. It occurs when dissimilar metals are in contact.
Many industries use sacrificial anodes to prevent the high value steel material from being corroded. Industrial pipes, steel hulled boats, bores, low pressure water tank, steel structures.
This galvanic corrosion works in our favour when trying to protect steel from being attacked by rust. Using a lesser value metal like magnesium or aluminium for the rust to attack is the most cost-effective way to significantly increase the life of a hot water tank. If routinely replaced as per the manufacturer’s recommendation, the life of a tank can potentially be infinite which will save thousands of dollars over the life of the tank.
Does water quality affect the rate of corrosion?
The quality of the water that goes into your tank can greatly impact the rate of corrosion. Total Dissolved Solids (TDS) combine the sum of all ion particles that are smaller than 2 microns (0.0002 cm) 11. This includes all of the disassociated electrolytes that make up salinity concentrations, as well as other compounds such as dissolved organic matter. The higher the TDS readings the higher the conductivity of the water and resultant damage from rust.
The other problem with hot water systems is the increasing conductivity as the temperature increases. Most storage tanks will keep the water temperature above 70+ degrees C to inhibit the growth of bacteria. Even for areas with very low TDS levels (ie clean rain water catchments), the increased water temperature will still have a corrosive effect.
My tank didn’t leak until it was at least 10 years old, and still hasn’t leaked?
Count yourself lucky. This is the problem of not seeing the damage until it’s too late. Once your tank leaks from corrosion, that’s well and truly too late to do anything about it. If the anode is never replaced, most tanks will last on average around 10 years, some areas less others more.
This is primarily due to the sacrificial anode working from day one. Once the anode has corroded to a point that it is no longer able to provide protection, the corrosive forces start to work on the tank itself. It’s only a matter of time that the tank will fail if the anode is not there to take the fall.
Most people don’t read the product information on their hot water system, but anodes are integral to the maintenance regime, just like maintenance on a vehicle, replacing the anode as per the manual is a small maintenance cost.
My plumber thinks replacing anodes is a waste of time?
It really depends on what type of work your plumber specialise in. Some plumbers prefer to sell you a new hot water system. There are however, other plumbers who focus on maintaining your existing system as per the manufacturer’s maintenance schedule and replace your anode as required.
Dealing with a plumber who’s prepared to maintain your tank over the years would get my business if a tank ever needed upgrading.
Magnesium or aluminium?
We stock both material types for anodes. The decision of which one to use comes down to your water quality.
If you have good quality water, Magnesium is the correct material. It provides the highest cathodic protection for your tank and is cheaper than aluminium anodes. Most suburban water supplies are considered good quality with a total dissolved solids (TDS) of less than 600 mg/L. If you are not sure, you can contact your local council to get information. If you have rainwater, clean dam or river water supplies this with also be good. If in doubt you should get your water tested.
If you have TDS reading of over 600mg/L then you need to use an aluminium anode to ensure you don’t get a chemical reaction with the magnesium which gives off a gas. The aluminium does not react with the water, so will still provide cathodic protection. If your existing anode has a blue cap, this is also an indication of an aluminium anode being used.