Failure analysis and characterization of Ferrous-Base alloy exposed in seawater environment

Abstract

Ferrous-base alloy are well-suited and widely used for a broad range of engineering applications such as structural steelwork, pipelines, vessels in refineries, thermal power plant establishment, etc. not for their corrosion resistance but for their reasonably good mechanical properties of strength, toughness, ductility and hardness; ease of fabrication and low cost. The study focused on determining the corrosion susceptibility of the ferrous-base alloy in presence of seawater environment in a stagnant condition under service condition. Corroded scraps ferrous-base alloy discarded after use in different seawater environments were collected for failure analysis to determine the causes of deterioration and degradation of alloy. The alloy samples as well as the deposits were investigated and characterized by using Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS) and Rockwell Hardness Test. The purpose is to trace the causes of failure mode; to check the nature and purity of the metal and corrosion deposits; to determine whether any unusual impurities has been present in the medium and to verify if the equipment confirms to the stated specification of fabrication and design. Immersed in seawater, the alloy of incomplete recrytallisation showed thick, loose and porous films, of which the outer layers contained a great amount of seawater species, and of which the underlying substrate was found with severe inter-granular, pitting & crevice corrosion