API 571 Certification (Corrosion & Materials) Practice Test

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Which type of stainless steel is noted for its resistance against caustic SCC?

400 series Stainless Steel
300 series Stainless Steel
Duplex Stainless Steel
Cast Stainless Steel

The correct answer is: Duplex Stainless Steel

Duplex stainless steel is particularly noted for its resistance to stress corrosion cracking (SCC) in caustic environments due to its unique microstructure, which is a combination of both austenitic and ferritic phases. This dual-phase structure provides enhanced strength and improved corrosion resistance compared to other stainless steel types. The ferritic phase contributes to toughness and resistance to stress corrosion cracking, while the austenitic phase offers ductility. This combination allows duplex stainless steel to withstand harsh conditions, including high pH environments, where caustic SCC commonly occurs. As a result, duplex stainless steel is often selected for applications where resistance to SCC in caustic solutions is crucial. Other types of stainless steels, such as the 400 series and 300 series, typically lack this beneficial combination of microstructural elements, making them more susceptible to SCC under similar conditions. Cast stainless steels also may not demonstrate the same level of resistance as duplex due to their composition and potential for casting defects.