API 571 Certification (Corrosion & Materials) Practice Test

What is a characteristic of duplex stainless steels concerning caustic SCC?

1. They are less resistant compared to austenitic steels.

2. They are more resistant than 300 series stainless steels.

3. They are significantly affected by temperature.

4. They are ineffective against all forms of corrosion.

The correct answer is: They are more resistant than 300 series stainless steels.

Duplex stainless steels exhibit a unique microstructure that comprises both austenite and ferrite phases, which gives them an enhanced resistance to stress corrosion cracking (SCC) in caustic environments compared to austenitic stainless steels, specifically the 300 series. Their higher chromium content, along with the balanced phase proportions, contributes to improved corrosion resistance, particularly in environments containing chlorides and caustic solutions. This dual-phase structure offers better strength and toughness, which are critical factors in resistance to SCC. The ability of duplex stainless steels to withstand caustic SCC is well-documented, making them a preferred material in applications where both strength and corrosion resistance are required, particularly in chemical processing and oil and gas environments. While temperature can affect the susceptibility to SCC and is also an important factor in determining the material's performance, it is the inherent properties of the duplex microstructure that primarily increase their resistance compared to 300 series stainless steels.