How can you detect corrosion in mechanical engineering applications?

2 Ultrasonic testing

Another common method for corrosion detection is ultrasonic testing. This involves sending high-frequency sound waves through the metal components and measuring the reflected waves. The sound waves can penetrate the metal and detect the thickness, shape, and defects of the components. Ultrasonic testing can be used to measure the extent of corrosion, such as the depth of pits, the size of cracks, or the loss of metal. Ultrasonic testing is fast, accurate, and non-destructive, but it requires skilled operators and proper calibration.

3 Electrochemical methods

Electrochemical methods are based on measuring the electrical properties of the metal components and the corrosive environment. For example, potentiostatic polarization involves applying a constant voltage to the metal component and measuring the current flow to determine the rate and type of corrosion reaction. Galvanic corrosion measures the potential difference between two different metals in contact with each other and the same electrolyte, which indicates which metal is corroding faster than the other. Lastly, electrochemical impedance spectroscopy involves applying a small alternating voltage to the metal component and measuring the impedance (resistance and capacitance) at different frequencies to determine the resistance of the metal to corrosion and the capacitance of the corrosion layer.

4 Chemical analysis

Chemical analysis is a method for corrosion detection that involves analyzing the chemical composition and properties of the metal components and the corrosive environment. This can be achieved through metallography, spectroscopy, and chromatography. Metallography involves preparing and examining the microstructure of the metal components with optical or electron microscopy to reveal grain size, phase distribution, defects, corrosion products, and damage. Spectroscopy exposes the metal components or corrosive environment to electromagnetic radiation and measures absorption, emission, or scattering of the radiation to reveal elements, compounds, and concentrations. Chromatography separates and identifies the components of a mixture using a stationary phase and a mobile phase to analyze corrosion inhibitors, contaminants, or by-products of the corrosion process.

5 Factors influencing corrosion

The rate and type of corrosion depend on various factors, such as the material, the environment, the stress, and the design of the mechanical engineering application. For example, iron is more prone to rust than stainless steel, and aluminum forms a protective oxide layer that prevents further corrosion. Seawater is more corrosive than freshwater, and acidic media are more corrosive than neutral or alkaline media. Additionally, cyclic stress can cause stress corrosion cracking, and tensile stress can cause hydrogen embrittlement. Design features can also create crevices, galvanic couples, or coatings that influence the corrosion process. Crevices can trap corrosive media and cause localized corrosion, galvanic couples can cause one metal to corrode faster than another, and coatings can prevent or delay corrosion. All of these factors must be taken into account in order to properly assess the risk of corrosion in a mechanical engineering application.