Failure analysis of propeller shaft used in the propulsion system of a fishing boat

This research aims to analyze root cause of the failure of propeller shaft used in the propulsion system of a fishing boat. The shaft was made of austenitic stainless steel type AISI-304 (18Cr-8Ni). The shaft was subjected to sulfur-containing atmosphere because of the biogas, especially hydrogen sulfide from fermentation of the sea fish. The severe fracture of shaft was found in service after two years. The failure analysis methodology such as fracture observation, mechanical and chemical composition testing, were basically investigated. The fracture observation showed apparently the low-stress fatigue fracture. It was found that the initial crack located on the shaft surface, showing possible pitting corrosion. In addition, some compound of sulfur such as iron sulfide was discovered in pitting hole due to the dissolution of H2S in brine. The electrochemical test was carried out by potentiodynamics with the mixture of H2SO4 and brine. The results showed apparently the effect of sulfur contamination on the corrosion behavior. The corrosion rate of sample submerged in 1% of H2SO4 is the highest. The corrosion mechanism and protection were further discussed in this research. (C) 2017 Elsevier Ltd. All rights reserved.