Failure analysis on circulating water pump of duplex stainless steel in 1000 MW ultra-supercritical thermal power unit

• Root causes of premature fractures on circulating water pump were identified.
• Lack of penetrations in weld joints was the first cause and its effect was discussed.
• Excessive ferrite in weld joints was another critical cause which was also discussed.
• Fracture process was illustrated and effective countermeasures were proposed.

With a large number of properties such as good mechanical properties and excellent corrosion resistance, 2205 duplex stainless steel (DSS) has been extensively used in many industries for the last decades. However, improper welding procedures will induce embrittlement of the weld joint, seriously decreasing the safety reliability of the weld joint. In this study, lots of unexpected fractures occurred on 2205 DSS which was used as the material for making circulating water pump (CWP) in an ultra-supercritical thermal power plant of China for the first time. By means of diverse characterization methods, comprehensive investigation was carried out on the failed CWP. Analysis results reveal that many lack of penetrations (LOPs) in the weld joint and unbalance ferrite/austenite ratio induced by improper welding procedures should be responsible for the fracture of the CWP. And effective countermeasures and suggestions were also proposed. So the analysis results have instructive significance for the fracture prevention of the CWP, even for ensuring safety operation of other equipment under similar seawater environment.

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