Mechanisms of Cracking of Austenitic-Ferritic Microstructure Steels In Corrosive Environment - Case Study

摘要

Mechanical and corrosion resistance are crucial requirements in materials selection for refinery and petrochemical industry equipments. The super duplex stainless steel presents such characteristics, which are attributed to its balanced 50% ferrite and 50% austenite microstructure, and it is widely used in this industry field. In this work, the morphology of cracking of a piece from the reboiler in service of the refinery sour water treatment unit was studied. This equipment piece is made of super duplex stainless steel SAF 2507 (UNS S32750). The results indicated that the cracking nucleation was due the hydrogen embrittlement and its propagation occurred through the ferritic grains. Those grains are more susceptible to hydrogen permeation and diffusion.