Introduction
One Eighty Materials Engineering was tasked with investigating the failure of ship engine components due to corrosion. The goal was to determine the root cause of the corrosion and provide insights into the materials used and their suitability for the corrosive environment.
Methodology
One Eighty Materials Engineering conducted a series of metallurgical tests on the engine components. The investigation involved visual inspection, optical examination, microstructural analysis, spectrographic analysis, Vickers hardness testing, and data comparison with known material specifications.
Results
Visual inspection revealed evidence of corrosion on all four engine components, with the most significant corrosion observed on the plungers. Macro-examination of the samples showed no deleterious features, except for a crack on one of the generator engine plungers. Microstructural analysis confirmed that the components were made of low-alloy steels suitable for engine applications. The chemical composition of the samples matched closely with AISI 4140, AISI 4130, and ASTM A485 Grade 1 bearing steel.
Spectrographic analysis of the samples identified contaminants such as sodium, chlorine, nitrogen, sulphur, iron, and manganese. The presence of significant amounts of chlorides indicated exposure to chlorinated hydrocarbons, as confirmed by a fuel sample analysis conducted by another laboratory.
Vickers hardness testing revealed that the hardness values of most samples were within the expected range for their respective materials. However, the generator engine plunger exhibited lower hardness values than expected, with a crack propagating through the harder region of the component.
Conclusion
Based on the investigation, it was concluded that the corrosion of the engine components occurred within a short duration, likely due to exposure to a corrosive contaminant. The presence of significant amounts of chlorides strongly indicated exposure to chlorinated hydrocarbons. The materials used, although suitable for engine applications running on acceptable fuels, were not specifically designed for contaminated chloride rich fuels.
Recommendations
One Eighty Materials Engineering provided the following recommendations based on their findings:
- Fuel sample analysis and assessment of fuel quality to determine the source of chlorine particles and monitor potential chlorinated hydrocarbon contamination.
- Continuous in-situ testing of fuels/oils during operation to detect any potential contamination. Periodic inspections are recommended during scheduled maintenance and refuelling.
Implementing these recommendations will help identify and mitigate potential sources of contamination and enhance the resistance of engine components to corrosion in similar environments.
