Prediction of Thermal Spray Coatings Performance in Marine Environments by Combination of Laboratory and Field Tests

Rosa Grinon-Echaniz,Rob Thornton,Shiladitya Paul,Marc Jeannin,Philippe Refait,Alvaro Rodriguez

doi:10.3390/coatings11030320

Abstract

Cost-effective corrosion mitigation of offshore steel structures can be achieved by thermal spray coatings. These coatings, when comprised of Al, Zn and their alloys, provide a physical barrier against the environment when intact, and cathodic protection to underlying steel when damaged. Due to the complexity of marine environments, laboratory tests should be combined with field work in order to understand the corrosion protection offered by these coatings. The work presented here was carried out with thermal spray coatings of aluminum alloys (AA1050, AA1100, Al-5Mg) and Zn-15Al prepared by Twin Wire Arc Spray onto low carbon steel substrates. The resulting coatings were ~300 μm in thickness, and 5% of surface area defects were artificially machined in order to expose the steel substrate, simulating mechanical damage or erosion of the coating. Electrochemical data collected over a 90 days period showed a good correlation between laboratory and real marine environment results. Aluminum alloys showed better corrosion protection in fully immersed conditions, while zinc alloys performed better in atmospheric and splash zones. Overall, these results aim to improve design of thermal spray coatings to protect carbon steel in marine environments.

Highlights

Marine environments are highly corrosive to metals, resulting in premature failure of offshore structures, ships, pipelines and bridges
Further optimization should be developed taking into account the effect of the environment which will aid the design of safer, low-cost offshore structures with low maintenance
This paper aims to provide a better understanding of the long-term offshore corrosion performance of Thermal Spray Aluminum (TSA) and TSZ (Zn-15Al) coatings

Summary

Introduction

Marine environments are highly corrosive to metals, resulting in premature failure of offshore structures, ships, pipelines and bridges. Thermal spray (TS) coatings have been used to mitigate marine corrosion for decades [1,2,3]. Since their introduction into the market, only limited improvements have been reported. Further optimization should be developed taking into account the effect of the environment which will aid the design of safer, low-cost offshore structures with low maintenance. Focusing on thermal spray coatings, they are made by finely dispersed deposition of molten or semi-molten particles onto a substrate. The general process consists of a high temperature and high velocity gas stream directing the coating material towards the substrate, where different types of heat source lead to different techniques: Flame spray, electric (or wire) arc spray and plasma arc spray [4]

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