Corrosion resistance at sea

Louise Smyth

With so much of the world still reliant on maritime transport, there is an international focus to drive down costs in the marine sector. This should not, however, come at the cost of material effectiveness for vital components like fasteners, as Ben Stafford, Materials Science Specialist at materials comparison site Matmatch explains.

Over the years engineers have found numerous ways of joining materials, from the use of adhesives to techniques like soldering and welding. Despite these developments, in the marine sector, mechanical fastening has remained the preferred choice by design engineers because of the secure and tight bond offered.                   
Being such a diverse market that covers the needs of shipyards, dry docks, oil rigs and even renewable wave technologies, the requirements for fasteners in the marine industry vary. But one common requirement among these applications is corrosion resistance, as salt water is highly corrosive because of its high concentration of dissociated ions.
Stainless steel has been the traditional material used for metal fasteners as it offers excellent corrosion resistance and strength at a reasonable price, but it is not the only material fit for the needs of the marine industry.
When selecting and designing components they must be engineered to endure the harsh marine environments, meaning mechanical properties are also critical. For example, non-corroding materials such as composites are very attractive in the marine sector for their lightness and mechanical strength, the use of which, however, is limited due to strict maritime regulations.
At the moment, such regulations tightly control the selection of materials which may be considered for marine applications. Nevertheless, there are still many suitable materials that engineers can turn to when choosing the right fastener, such as brass.
At Matmatch, our material scientists have found brass to be a suitable choice for marine applications because it boasts the high corrosion resistance required to handle the environmental conditions.
Statistics have shown that as the hull materials for marine vessels make the transition to lightweight materials, this will raise the demand for lightweight and high-performance fasteners. This could be achieved with polymer-based materials. But while you could expect a metal to corrode under water, some polymers can have a tough time above sea level. This is because it is common for some polymers to degrade when exposed to UV radiation.
Nevertheless, plastics like polyvinylidene fluoride (PVDF) have UV-resistant properties, meaning they will not degrade in the sun or become brittle with age and compromise the strength of the fastener.
As we’ve identified with the marine industry, there is more to consider than meets the eye. Will your fasteners be fit for purpose above and below sea level, or do you need to consider multiple materials for your specific application?
Eliminating the materials that are not suitable in marine environments may seem like a test of common sense but often when you refine the ‘go-to’ or traditional choices, engineers find there is more to consider. Whether it’s to reduce cost or increase strength and reliability, engineers should consider the environment their components will be used in when making their material choice and select accordingly using a reliable materials database.

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