Flow accelerated corrosion and erosion\u2212corrosion behavior of marine carbon steel in natural seawater

Yunze Xu,Bin Wang,Shan Gao,Yi Huang,Xiaona Wang,Qipiao Zhou,Qiliang Zhang

doi:10.1038/s41529-021-00205-1

Abstract

In this work, flow accelerated corrosion (FAC) and erosion−corrosion of marine carbon steel in natural seawater were electrochemically studied using a submerged impingement jet system. Results show that the formation of a relatively compact rust layer in flowing natural seawater would lead to the FAC pattern change from ‘flow marks’ to pits. The increase of the flow velocity was found to have a negligible influence on the FAC rate at velocities of 5−8 m s−1. The synergy of mechanical erosion and electrochemical corrosion is the main contributor to the total steel loss under erosion−corrosion. The increase of the sand impact energy could induce the pitting damage and accelerate the steel degradation. The accumulation of the rust inside the pits could facilitate the longitudinal growth of the pits, however, the accumulated rusts retard the erosion of the pit bottom. The erosion and corrosion could work together to cause the steel peeling at the pit boundary. The steel degradation would gradually change from corrosion-dominated to erosion-dominated along with the impact energy increasing.

Highlights

Carbon steels are extensively used in ocean engineering applications due to their low cost and high mechanical strength[1,2,3].Because of the low contents of Ni and Cr elements, the passive film cannot form on the surface of carbon steel, leading to the steel degradation under active corrosion in seawater[4,5]
Surface characterizations indicated that a more dense rust layer formed on the carbon steel in the flowing natural seawater than that in the flowing 3.5 wt% NaCl solution, which effectively protected the steel from flow accelerated corrosion (FAC)
The generated rust layer would become porous and lose its protective effect in stagnant seawater[2,8]. These findings suggest that the influence of the flow velocity on the FAC of carbon steels should be further studied in consideration of the corrosion product layer

Summary

Introduction

Carbon steels are extensively used in ocean engineering applications due to their low cost and high mechanical strength[1,2,3].Because of the low contents of Ni and Cr elements, the passive film cannot form on the surface of carbon steel, leading to the steel degradation under active corrosion in seawater[4,5]. The contact between steel structures and moving seawater might induce flow accelerated corrosion (FAC) and erosion−corrosion[6,7,8,9]. Such issues are more obvious in high-speed vessels and underwater vehicles, where cruising speeds could reach above 10 m s−110–12. Recent studies[2,22] showed that apart from the flow velocity, the rust layer formed on the steel surface in natural seawater played an important role on the FAC behaviour. Surface characterizations indicated that a more dense rust layer formed on the carbon steel in the flowing natural seawater than that in the flowing 3.5 wt% NaCl solution, which effectively protected the steel from FAC

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Conclusion