Sigma phase is a deleterious phase which can be formed in duplex stainless steels (DSSs) during heat treatment, manufacturing, or welding processes, leading to a decrease of mechanical properties and corrosion resistance. This issue is highly concerning for numerous industries because the presence of σ–phase in the austenite/ferrite microstructure of DSSs reduces their lifetime and promotes a brittle fracture in service. This review focuses on the non-destructive techniques (NDT) for the detection of σ–phase and their application in engineering failure analysis and field study cases in recent years. The most used NDT as inspection tools are ultrasound (US) and magnetic techniques; there are further alternative methods such as electrochemical potentiokinetic reactivation (EPR) technique and replication metallography (RM) analysis. Their advantages and drawbacks are discussed and exemplified with case studies. The current trend for NDT applied to the σ–phase is thoroughly studied and represented, showing the key mechanisms and factors influencing σ–phase formation and its consequences on DSSs. In addition, a detailed description of important failure cases wherein σ–phase has been responsible is presented.

Sigma相是一种有害相，可以在热处理，制造或焊接过程中形成于双相不锈钢（DSS）中，导致机械性能和耐腐蚀性下降。这个问题引起了许多行业的高度关注，因为DSS的奥氏体/铁素体微结构中存在σ相会缩短其寿命并促进使用中的脆性断裂。这篇综述着重于检测σ相的无损技术（NDT）及其在近年来的工程故障分析和现场研究案例中的应用。最常用的NDT作为检查工具是超声（US）和磁技术。还有其他替代方法，例如电化学电位动力学激活（EPR）技术和复制金相（RM）分析。讨论并举例说明其优缺点。深入研究了无损探伤目前应用于σ相的趋势，并进行了描述，它显示了影响σ相形成及其对DSSs产生影响的关键机制和因素。此外，还提供了对重要的失效案例的详细描述，其中σ相已成为原因。