Ground-level and elevated steel tank for storing water is an integral part of a water distribution system. It ensures adequate water pressure and enough supply of clean, potable drinking water. It also serves as a landmark for most communities. But if these bolted tanks are not properly maintained, they become a significant liability to the community not only to the household it serves. Poor maintenance could lead to corrosion-generated leaks and potential service interruptions or worse, a health hazard. Today, there are high-performance water tanks and high stable coating system that is available in the market to help avoid corrosion on water tanks. Aside from meeting Volatile Organic Compounds or VOC regulations, these tanks have environmentally-friendly coatings that offer finish quality and application advantages compared to traditional solvent-based coatings. These environment-friendly coatings create a mechanical bond with steel substrates on new reservoirs and provide a far superior adhesion compared to layers used by older tanks. They are also compatible with cathodic coatings. By knowing the cause of corrosion on storage water tanks and the characteristics of high solids and waterborne coatings is an effective and economical way to maintain the tanks.
All portable storage water tanks are susceptible to corrosion and other metal and steel problems. Finding the best coating for maintaining the water tank starts with the assessment of the corrosive factors present inside or outside the container.
We all know that corrosion is a natural phenomenon based on chemistry, electricity, and metallurgy. When refining and smelting iron ore to produce steel used in storage water tank construction, energy is added. It will result in energy imbalance. Nature will do its work to fight this imbalance by releasing the energy back in the form of electrons. It will cause the steel to corrode and return to being iron oxide, or as we know, rust. You can compare the process of corrosion to a stone being rolled up a hill. For example, if you push a rock higher up the hill, the energy you exerted will expand. Once the excess energy is removed, the stone will begin to roll down the mountain and slowly loses its energy until it reaches the bottom of the hill. In the same way, metals, especially steel contain a certain amount of energy, and it slowly loses its energy over time.
For corrosion to occur, three elements need to be present: metal, oxygen, and electrolyte. Areas with high energy that corrodes are called anodes, and the area that receives the released energy is called the cathode. Cathode and anode are made of the same alloy, same structure with steel that is used in water storage tanks. Metal will act as a conductor, and the area on the steel are those that corrodes. Electrolyte will serve as a medium that will surround the metals to transfer energy and current flow. It will serve a significant role in the corrosion process. An electrolyte with low conductivity will produce less corrosion and vice versa. Because the inner side of the tank has water, which is a good conductor of electricity, it will generate more rust compared to the outside part of the container which has less to no electrolyte available.
(To know more about the process of corrosion, visit https://xapps.xyleminc.com/Crest.Grindex/help/grindex/contents/Metals.htm)
Using a protective coating or cathode protection in both the exterior and interior part of the storage tank will help prevent corrosion. It will have economic benefits to the community, including lower operating cost, extended life of the tank and fewer repairs. But since tanks used for potable water are in the different corrosive environment, the coating and protection applied inside and outside the tank also differ. The exterior of the container can use coat alone. It will protect the tank from chemical compounds and moisture as well as ultraviolet radiation from the sun. Inside protection is a little bit different. Stronger coating with higher dialect strength is used to prevent the ion transfer and current flow. With a less ion transfer, the corrosion process is stopped. It is imperative to coat the water storage tank properly. One small crack or uncoated part will expose the metal to the electrolyte and can cause corrosion that will spread all over the tank eventually. Make sure to coat every inch of the tank, inside and outside.