API 571 Certification (Corrosion & Materials) Practice Test

Which of the following materials is most susceptible to ethanol stress corrosion cracking?

1. Duplex stainless steel

2. Carbon steels

3. Copper alloys

4. High-strength steels

The correct answer is: Carbon steels

Ethanol stress corrosion cracking is primarily a concern for certain materials when they are in contact with ethanol or ethanol-blended fuels. Carbon steels are particularly susceptible to this type of cracking due to several factors related to their microstructure and mechanical properties. In the case of carbon steels, the presence of moisture, along with the aggressive environment provided by ethanol, can lead to the initiation and propagation of stress corrosion cracks. The carbon in the steel can make it more prone to this type of mechanical degradation, especially under tensile stress. The reaction between the ethanol and carbon steel can create localized corrosion sites, which can serve as origins for cracks. This degradation process can be further accelerated in the presence of high tensile stresses and microscopic flaws in the material. Other materials, like duplex stainless steels and copper alloys, typically exhibit much better resistance to stress corrosion cracking in ethanol environments due to their alloying components and microstructures which help prevent crack initiation and propagation. High-strength steels can be susceptible as well, but they do not show the same level of vulnerability as carbon steels in ethanol. In summary, carbon steels face significant risks for stress corrosion cracking when exposed to ethanol, making them the most susceptible material in this context.