AN INVESTIGATION OF CORROSION BEHAVIOR OF CAST IRON PIPES

ABSTRACT

It is well known that corrosion is the predominant mechanism for the deterioration of cast iron pipes, leading to the reduction of pipe capacity and ultimate collapse of the pipes. In order to assess the remaining service life of corroded cast iron pipes, it is imperative to understand the mechanisms of corrosion over a long term and to develop models for pipe deterioration. The present research intends to determine the corrosion rate and observe the corrosion behavior of grey cast iron pipe in the different environment present in the Niger Delta area of Nigeria in other to see which of this medium exerts the worse corrosion damage on the cast iron material. In this research, an experimental program is presented in which the corrosion behavior of grey cast iron pipes was thoroughly examined in three different environments. Gravimetric weight loss method was adopted in the study. Coupons were cut to approximate size (42mm x 35mm x 9.8mm) of rectangular shape for easy calculation of surface area. SEM and XRD Images of several coupons were also examined in other to have a detailed surface analysis of surface morphology of the corroded materials and products. It was found in this research that uniform corrosion and localized corrosion are the primary forms of corrosion of cast iron water pipes. It has also been found that the microstructure of cast irons is a key factor that affects the corrosion behavior of cast iron pipes. The corrosion rates obtained for seawater specimen of cast iron immersed for 90days with 15days specimen evaluations intervals show a steady rise of metal loss to corrosion of about 0.03% to 0.46%, for the river water specimen a trend of 0.07% to 1.5% and finally for Fresh water specimen a trend of 0.084% to 1.89% loss was recorded. The corrosion rates for seawater rises steadily from (0.0088 to 0.0229)mg/cm²/yr, for freshwater (0.0246 to 0.0904)mg/cm²/yr and finally for river water (0.0207 to 0.0707)mg/cm²/yr. This research concludes that long-term tests on corrosion behavior of cast iron pipes can help develop models for corrosion-induced deterioration of the pipes for use in predicting the remaining service life of the pipes.