Corrosion failure analysis of duplex stainless steel in marine environment

Serious crevice corrosion was detected at wear ring and pump casing of an S32760 duplex stainless steel fire pump assembled on an offshore platform, which resulted in broken of the wear ring. The failure mechanism of the cracked wear ring was analyzed, and results showed that the chemical composition of the wear ring corresponds to the standard S32760. However, metallographic test results showed that the wear ring has many harmful σ-phases and inclusions in the matrix, which led to the decrease of corrosion resistance of the material and induced crevice corrosion at the bolt joint and the wear ring. Besides, Chloride, sulfide, sodium and potassium have been found at corrosion products and pump casing fragments through energy dispersive X-ray spectrometry. Thus, to extend the service life of the fire pump, better sealing measures are needed to prevent crevice corrosion.