API 571 Certification (Corrosion & Materials) Practice Test

What material is listed as most susceptible to soil corrosion?

1. Cast Iron

2. Ductile Iron

3. Alloy 800

4. Carbon Steel

The correct answer is: Carbon Steel

Carbon steel is recognized as the material most susceptible to soil corrosion due to its electrochemical properties and the conditions typically found in soil environments. When carbon steel is buried or comes into contact with moist soil, it can form localized corrosion cells. This is mainly because the presence of moisture and various chemicals in the soil can create an electrolyte conducive to corrosion processes, particularly in the presence of oxygen. Soil can also contain chlorides, sulfates, and other corrosive agents that may accelerate the corrosion of carbon steel. Moreover, the relatively low alloy content in carbon steel means it lacks the protective alloying elements found in other materials like stainless steels or certain alloys, making it more vulnerable to aggressive corrosion in soil conditions. In contrast, materials such as cast iron and ductile iron, while still susceptible to corrosion, have different compositions and often better resistance to certain corrosion processes due to their additional graphite content or treatment that can enhance their protective characteristics. Alloy 800, being a high-temperature nickel-chromium alloy, is designed for strength and oxidation resistance, making it far less prone to corrosion in soil environments compared to carbon steel.