API 571 Certification (Corrosion & Materials) Practice Test

What is the susceptibility of Alloy K-500 when subjected to HF stress corrosion cracking?

1. Highly resistant

2. Moderately resistant

3. Very susceptible

4. Immune

The correct answer is: Very susceptible

Alloy K-500, which is a precipitation-hardened nickel-copper alloy, is known to be very susceptible to stress corrosion cracking in the presence of hydrofluoric acid (HF). The unique characteristics of this alloy, including its high strength and corrosion resistance under many conditions, do not translate well in the specific environment of HF. In the context of HF, stress corrosion cracking can occur due to the combination of tensile stress and the aggressive nature of the acid, which can attack the alloy in a manner that decreases its structural integrity. This susceptibility is a significant concern in industries that handle HF, making understanding the behavior of Alloy K-500 in these conditions crucial for materials selection and process design. Other options suggest varying levels of resistance or immunity to stress corrosion cracking, which do not accurately reflect the alloy's real interaction with HF. The actual risk associated with Alloy K-500 is well-documented, reinforcing that it is indeed very susceptible in this environment, necessitating careful consideration in application and engineering practices.