Visual Testing (VT) Practice Exam

What type of corrosion occurs due to the contact of dissimilar metals in a corrosive medium?

1. Selective leaching

2. Galvanic corrosion

3. Crevice corrosion

4. Stress corrosion

The correct answer is: Galvanic corrosion

Galvanic corrosion occurs when two dissimilar metals are in electrical contact within a corrosive environment. This type of corrosion is driven by the electrochemical reaction that takes place between the two different metals. When these metals are connected, one metal acts as the anode (which corrodes more quickly), while the other acts as the cathode (which is protected from corrosion). The presence of an electrolyte, such as water or acidic solutions, facilitates the flow of ions between the metals, enhancing the corrosion process. This phenomenon often occurs in marine environments or other settings where different metals are used together. In contrast, the other types of corrosion mentioned do not primarily involve the interaction between dissimilar metals. Selective leaching refers to the preferential dissolution of one or more components from an alloy. Crevice corrosion occurs in sheltered areas where stagnant solution can lead to localized attacks. Stress corrosion is related to the combined effects of tensile stress and a corrosive environment on a material. Understanding galvanic corrosion is crucial for preventing accelerated deterioration of metals that are used in conjunction with others, especially in industries like construction, automotive, and marine applications.