API 571 Certification (Corrosion & Materials) Practice Test

Which of the following materials is particularly susceptible to stress relaxation cracking?

1. 304H Stainless Steel

2. 1.25Cr Steel

3. Aluminum Alloy

4. Carbon Steel

The correct answer is: 1.25Cr Steel

The susceptibility of materials to stress relaxation cracking is influenced by their metallurgical properties and conditions of service. In this case, 1.25Cr Steel, which contains chromium for improved oxidation resistance, is particularly vulnerable to stress relaxation cracking, especially at elevated temperatures. Stress relaxation cracking occurs when a material, under constant load, experiences a gradual reduction in its ability to sustain that load due to a decrease in internal stresses, often associated with creep behavior at high temperatures. 1.25Cr Steel is commonly used in high-temperature applications, such as in pressure vessels and piping systems. The combination of high temperature and sustained stress makes it more prone to this type of cracking compared to the other materials listed. On the other hand, 304H stainless steel, while it can also be affected by stress-related issues, tends not to exhibit the same level of sensitivity to stress relaxation cracking under similar conditions. Aluminum alloys generally have different failure mechanisms and typically do not experience stress relaxation cracking in the same sense as ferrous alloys. Carbon steel, while susceptible to various forms of corrosion and mechanical stress, is less prone to stress relaxation cracking compared to high-alloy steels like 1.25Cr due to its different microstructural characteristics. Overall, 1