Comparative Study of Corrosion Resistance of Marine Grade Carbon Steels X65 and MS in the Cochin Estuary Environment

Abstract

This study aims to investigate the corrosion behavior of API 5L-X65 and IS 2062 GR A mild steel (MS) material exposed to the challenging environmental conditions of Cochin Estuary sediment. Utilizing a combination of experimental and analytical methodologies, the current research involves the immersion of X65 and MS test specimens in Cochin Estuary sediment for a time period of 168 h to simulate real-world conditions. In parallel, a set of experiments in sterile conditions is also conducted for comparison. Under sterile and sediment conditions, the corrosion characteristics were analyzed at 24, 72, 120, and 168 h of immersion. Various techniques, including electrochemical impedance spectroscopy, potentiodynamic polarization, scanning electron microscopy, and X-ray diffraction, were used to examine corrosion rates, corroded surface morphologies, and corrosion product analyses. The results of this study indicates that the corrosion rate of the coupons X65 and MS are being accelerated under Cochin Estuary sediment conditions. After 168 h of immersion, the charge transfer resistance (Rct) for X65 and MS in sediment conditions was 9.48 and 7.95 Ω cm2, respectively, indicating that X65 is less susceptible to corrosion compared to MS in sediment condition. The XRD data obtained for the analysis of corrosion products under sediment conditions revealed the presence of an iron sulfide mineral known as smythite (Fe3S4), suggesting the existence of sulphate-reducing bacteria. This finding serves as strong evidence for the occurrence of microbially induced corrosion (MIC) in Cochin Estuary sediment conditions. In short, this research gives a systematic comparison of the corrosion characteristics of X65 and MS materials under Cochin Estuary sediment conditions, providing a foundation for selection of materials and corrosion prevention strategies in marine and coastal applications. The results of this study have a significant impact on the design, construction, and maintenance of coastal infrastructure, specifically in offshore and submarine conditions. This study involves the understanding of corrosion behavior of X65 and MS in postmonsoon Cochin Estuarine sediment environment; it also provides significant expertise in the development of various marine industries such as oil and gas, renewable energy, maritime and shipping, shipbuilding, etc. The findings of this study can assist material selection for subsea pipelines, offshore platforms, and any structural elements in direct exposure to marine environments, helping engineers to reduce the annual maintenance cost by improving the performance and durability of the structural components. Moreover, this study helps to perform a comparative cost-benefit analysis of X65 and MS, which can guide industry stakeholders to balance material durability and economic feasibility. It also considered the role of microorganisms in corrosion under Cochin Estuarine sediment conditions as an example, contributing to the development of more efficient and cost-effective mitigation strategies.