A failure analysis study of wet liners in maritime diesel engines

Abstract

This paper presents the results of a study regarding the failure mechanisms detected in alloyed cast iron liners of marine engines. The liners have shown cracks and extensive corrosion after about 1200 service hours, located in the adjustment flange between the liners in the cylinder block. This study includes the material characterisation using chemical, microstructural, hardness and fractographic analysis. The metallurgical results have shown that the material was acceptable concerning the composition and microstructure. The paper also presents the results obtained for the distribution of stresses and temperatures in the critical areas of the cylinder liner. A 2D finite element code was used for this study, using axisymmetric elements with reduced integration. The results have shown that the thermal stresses are significantly more important than the mechanical stresses, the latter being due exclusively to the effect of the combustion gases in the cylinder. For the two geometries which were analysed, the peak stresses were slightly above 100 MPa in tension. This value of stress is high for the cast iron of the liners, and leads to a great potential risk of initiation and propagation of the tiny surface corrosion defects found in these zones. The detailed geometric changes introduced in the second design of the liner gave a little improvement in the stress distribution in the critical areas, although this may not be enough to avoid cracking conditions in the critical areas.