What Does Corrosion Resistance Mean?
Corrosion resistance is defined as the inherent ability of a material (metallic or non-metallic) to withstand corrosion damage caused by either oxidation or other chemical reactions. Resistance to corrosion can be achieved either through the intrinsic resistant properties of the material or by using corrosion resistant products/substances such as paints, coatings or corrosion inhibitors.
Corrosion resistance determines the maintenance schedule of sewer pipelines and is an important factor in deciding the time frame that this should be done in. This makes it similar to corrosion rate. Some metals are not very resistant to corrosion such as steel and reinforced concrete. This is especially true when the corrosion is caused by sulfuric acid that is produced by bacteria.
Corrosion is a process in which a material is oxidized by substances in the environment that cause the material to lose electrons. Corrosion resistance is the capacity to hold the binding energy of a metal and withstand the deterioration and chemical breakdown that would otherwise occur when the material is exposed to such an environment.
Corrosion resistance is an important factor to consider when selecting materials for corrosion control. The materials most resistant to corrosion are those for which corrosion is thermodynamically unfavorable. Some metals have naturally slow reaction kinetics, even though their corrosion is thermodynamically favorable. These include metals such as zinc, magnesium and cadmium. Thus, both a material's own resistance to corrosion and protective methods to arrest corrosion fall under the category of corrosion resistance.
Corrosionpedia Explains Corrosion Resistance
Corrosion is the loss of metal due to a reaction with the environment, and is measured as the percentage of loss in weight or as the penetration rate of the corrosion, normally measured in inches per year.
Usually, the resistance to corrosion is expressed in terms of the corrosion rate and measured in units of millimeter per year or "mils." These measurements for resistance to corrosion attack are taken in a particular environment at defined operating conditions, pressure, temperature and fluid velocity.
Besides intrinsic corrosion resistance, a metal's resistance to corrosion can be increased by applying different methods such as cathodic protection, coating, painting and applying a corrosion inhibitor. There are no materials that are resistant to all corrosion in all environments. Materials must be matched to the environment they will experience.
Corrosion can develop in the presence of liquids or gases. It may occur at any temperature, although generally the rate of corrosion increases with increasing temperature. Corrosion associated with liquids is often caused by impurities or by trace elements within the liquid. Examples of that would be the presence of chlorine, which results in formation of hydrochloric acid, or of sulfur, which subsequently forms sulfuric acid.
It is important to remember that any alloy, stainless steel or otherwise, can corrode under certain conditions The presence of corrosion may not indicate a faulty product; it may instead indicate an improper application of that product – perhaps we may be using a material that is not the best suited for a given environment,
Corrosion resistances for metals are estimated and data is used to check the sustainability of a metal in a particular environment.
Corrosion resistant metals, particularly stainless steels, form a very thin chromium oxide layer that protects the next layer of metal from oxygen. That is important because oxygen is needed with iron to create rust/iron oxide. In general, if there is no oxygen, there is no rust. The layer is passive – the process is known as passivation – and self-healing; if the surface is scratched, the oxide layer regenerates itself if there is oxygen present.
Protective coatings are the most widely used corrosion control technique. Essentially, protective coating materials are a means for separating the surfaces that are susceptible to corrosion attack. Another method, cathodic protection, interferes with the natural action of electrochemical cells that are responsible for corrosion. Cathodic protection can be effectively used to resist corrosion of surfaces that are immersed in water or exposed to soil.
Apart from protective coatings, there are many other ways of ensuring corrosion resistance in a metal. Design of the metal part being one of them in engineering. In a case where the part in question is intended for use in an environment that could subject it to corrosion it should be designed with that taken into consideration.
Environmental control helps keep materials being used safe from corrosion by taking simple measures to ensure they are clean and dry. By controlling these environmental factors, the likelihood of corrosion occurring is also being mitigated.
Cathodic protection is a possible way to prevent corrosion by applying an opposing electric current to a metals surface. There are different methods of cathodic protection. One is by the use of an impressed current whereby with the use of an outside course of electric current a corrosive current is overpowered in the part. Another method is by the use of a sacrificial anode. In this method metal ions will flow from the reactive metal to the less active part thereby reducing corrosion in one at the expense of the other.
Overall maintenance is the most effective way of preventing corrosion in metals and other materials that can be subject to wear and corrosion.