Galvanising transformer radiators will improve their life expectancy

Power transformers are manufactured with a combination of HR and CR steel, which are long-lasting constructions with an expected life span of up to 25–40 years. Radiators with several elements made from 1 mm to 1.2 mm CR steel must withstand the corrosive attack due to environmental conditions. Compared to conventional corrosion protection, hot-dip galvanising is a long-lasting and durable type of corrosion protection. As shown in Figure 1, the corrosion protection of a hot-dip galvanised radiator could have an estimated life of up to 40 years. However, conventional coatings must be renewed every 4–5 years. If galvanising is used for corrosion protection, it may last up to 25–40 years, equal to the lifespan of a power transformer.

 How zinc protects the radiator
Steel is a very versatile product, and radiators are produced with steel. Unfortunately, it is prone to rusting, a phenomenon that causes the surface to become unsightly and, over time, may contribute to product failure. For this reason, radiators are protected by various methods ranging from internal alloying, e.g., stainless steel, to coating with galvanised coatings and/or paints. Corrosion is an electrochemical process that, in the case of steel, oxidises the iron in the steel and causes the steel to become thinner over time. Oxidation, or rusting, occurs due to the chemical reaction between steel and oxygen. Oxygen is always present in the air or can be dissolved in moisture on the surface of the steel sheet. During the rusting process, steel is consumed during the corrosion reaction, converting iron into corrosion products. In the case of most low-carbon steel sheet products, iron oxide (rust) develops on the surface and is not protective because it does not form a continuous, adherent film. Instead, it spalls, exposing fresh iron to the atmosphere, which, in turn, allows more corrosion to occur. This aspect of steel behaviour is undesirable, both aesthetically and in terms of service life. Eventually, often sooner than desired, steel corrodes sufficiently to unduly shorten its service life, i.e., loss of structural strength or perforation and water intrusion.

Galvanised coating in a hot dip
Hot-dip galvanised coating is a well-developed method of protecting radiators from corrosion and provides it in two ways:
Like paint, they provide barrier protection and galvanic protection.
These protection mechanisms are described below.
Barrier Protection: The primary mechanism by which galvanised coatings protect steel is by providing a waterproof barrier that does not allow moisture to contact the steel since there is no corrosion without moisture (electrolyte). The nature of the galvanising process ensures that the metallic zinc coating has excellent adhesion, abrasion, and corrosion resistance. Galvanised coatings will not degrade (crack, blister, and peel) as with other barrier coatings such as paint. However, zinc is a reactive material and will corrode and erode slowly. For this reason, the protection offered by a galvanised coating is proportional to its thickness and corrosion rate. It is, therefore, essential to understanding zinc’s corrosion mechanism and what factors affect the rate. Freshly exposed galvanised steel reacts with the surrounding atmosphere to form zinc corrosion products. In the air, newly exposed zinc reacts with oxygen to form a thin, tenacious zinc oxide layer. When moisture is present, zinc reacts with water, resulting in the formation of zinc hydroxide. The final corrosion product is zinc carbonate, which forms when zinc hydroxide reacts with carbon dioxide in the air. Zinc carbonate is a thin, tenacious, and stable (insoluble in water) layer that protects the underlying zinc and is the primary reason for its low corrosion rate in most environments.
Galvanic (cathodic) protection: The second shielding mechanism is zinc’s ability to protect steel galvanically. When base steel is exposed, such as at a cut edge or scratch, the steel is cathodically protected by the sacrificial corrosion of the zinc coating. This occurs because zinc is more electronegative (more reactive) than steel in the galvanic series, as shown below.