Methods of expressing corrosion rate

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      Corrosion is the type of wear that causes the greatest losses. The weight of metal material lost per unit area per unit time, or the average concentration thickness of metal material loss per unit time, is referred to as the corrosion rate. In practical applications, the analysis of corrosion rate and its causes is primarily useful for estimating the service life of components, and it serves as an important indicator for assessing a metal’s corrosion resistance. The corrosion grade of metal materials is also defined by their corrosion rate. 1. Methods of expressing corrosion rate: 1.1 Mass change method – The corrosion rate is expressed as the change in mass per unit area per unit time; the commonly used unit is milligrams/(decimeter·day), abbreviated as mdd ； 1.2 Representation of corrosion depth: The corrosion rate is expressed as the amount of corrosion that occurs per unit of time, with the commonly used unit being millimeters per year (mm/a) ； 1.3 Mechanical strength notation: Applicable for indicating certain special types of corrosion, namely those for which the corrosion rate cannot be accurately reflected by the first two notations, such as stress corrosion cracking and cavitation. This type of corrosion is often accompanied by a decrease in mechanical strength. It is possible to test the changes in strength before and after corrosion, represented by the rate of decrease in limits such as tension, pressure, bending, or impact ； Using corrosion current density to represent the corrosion rate is an electrochemical testing method. The commonly used unit is microamps per centimeter. 2. Methods for expressing corrosion depth 2.1 The first category corresponds to materials that are completely resistant to corrosion: the corrosion rate is less than 0.1 mm/year; high-quality stainless steels belong to this category of materials. A corrosion rate of 10 indicates a material that is not resistant to corrosion.