API 571 Certification (Corrosion & Materials) Practice Test

Which stainless steel type is preferable to reduce the risk of sensitization in corrosive environments?

1. 304 SS

2. 301 SS

3. 316 SS

4. 305 SS

The correct answer is: 304 SS

The goal of reducing the risk of sensitization in stainless steels, especially in corrosive environments, is particularly important in applications where the material may be exposed to temperatures above 800°F (427°C). Sensitization occurs when carbon and chromium react in such a way that chromium carbides precipitate at grain boundaries, depleting the chromium content in those areas and making the steel more susceptible to intergranular corrosion. Type 304 stainless steel is austenitic and has a high chromium content (around 18%) with lower carbon content compared to some other grades. Its composition helps in minimizing the risk of sensitization, especially in environments that do not require elevated resistance to chloride-induced stress corrosion cracking. The balanced alloying elements make it durable against corrosion while still maintaining good formability and weldability. While other grades like Type 316 offer better overall corrosion resistance due to the presence of molybdenum, they are not inherently better in reducing sensitization compared to Type 304, particularly under certain service conditions. Grades like 301 and 305 can also be susceptible to sensitization, especially if subjected to specific thermal cycles. Overall, Type 304 stainless steel is widely recognized as a good choice for reducing sensitization risks due to its