API 571 Certification (Corrosion & Materials) Practice Test

What is the sequence of steel types in order of increasing resistance to high temperature hydrogen sulfide corrosion?

1. Low Alloy Steel, CS, 300 series stainless, 400 series stainless

2. CS, Low Alloy Steel, 400 series stainless, 300 series stainless

3. CS, 400 series stainless, Low Alloy Steel, 300 series stainless

4. CS, 300 series stainless, Low Alloy Steel, 400 series stainless

The correct answer is: CS, Low Alloy Steel, 400 series stainless, 300 series stainless

The correct sequence of steel types in order of increasing resistance to high-temperature hydrogen sulfide (H2S) corrosion is based on the material properties and the effects of H2S on various steel grades. Carbon Steel (CS) typically has the least resistance to high-temperature hydrogen sulfide corrosion. It is susceptible to sulfide stress cracking and general corrosion when exposed to H2S environments, especially at elevated temperatures. Low Alloy Steel is an improvement over carbon steel regarding strength and resistance to various forms of corrosion, including H2S. However, it still does not possess the same level of corrosion resistance as stainless steels. As we consider the stainless steels, the 400 series stainless steels are known for their moderate resistance to H2S corrosion. They are primarily ferritic and can perform reasonably well in H2S environments but lack the enhanced resistance seen in the austenitic stainless steels. The 300 series stainless steels, which are austenitic, provide superior resistance to hydrogen sulfide corrosion due to their nickel content and other alloying elements that enhance their overall corrosion resistance and mechanical properties. This makes them the most effective choice for high-temperature H2S environments. Thus, the progression of resistance is correctly represented in the chosen option, which outlines