Egenskapene til legeringen EN 1982 i sjøvann under påvirkning av et sterkt magnetisk felt. Corrosion of EN 1982 in a magnetic field.

Nickel-aluminium bronze (NAB) is commonly used in propellers and pumps in seawater, where the demand for corrosion resistance is high. The alloy performs well, and is widely used in such applications, but problems have occurred when the alloy has been in galvanic coupling to stainless steel and exposed to strong magnetic fields. The industrial PhD was initiated with a clear goal to document any correlation or synergistic effects between corrosion (electrochemistry) and electromagnetism. The research was based on experimental work in laboratories, where the corrosion properties of NAB were tested under different conditions, i.e. in galvanic coupling to stainless steel in natural seawater, under the influence of a uniform and constant magnetic field, or under the influence of a time-dependent magnetic field. The results showed that the alloy suffers galvanic corrosion when coupled to stainless steel in natural seawater, and that both a static and a time-dependent magnetic field may accelerate the corrosion rate of NAB under such conditions. Based on these results, it was concluded that NAB should not be used together with stainless steel in natural sweater without any protection such as paint or cathodic protection, and that NAB should not be exposed to seawater when simultaneously exposed to magnetic fields. The results generated a change in the design of a commercial product, as a step towards increasing the lifetime and robustness of the product.

Prosjektets hovedmål er å kartlegge legeringen EN 1982 sine egenskaper i sjøvann under påvirkning av et sterkt magnetisk felt. Den sentrale problemstillingen i prosjektet er hvordan et magnetfelt kan påvirke oppbygningen og/eller nedbrytningen av et tett oksidsjikt på legeringen i kontakt med sjøvann. Dette oksid-sjiktets natur bestemmer korrosjonsbestandigheten til legeringen, og er derfor avgjørende for legeringen sine prestasjoner i undervannsapplikasjoner. Denne problemstillingen vil angripes ved å ut føre en rekke korrosjons-eksperimenter på legeringen under påvirkning av et sterkt magnetisk felt i et sjøvannslaboratorium. Da andre faktorer som katodisk beskyttelse, forurensninger i sjøvann og mikrostruktur i legeringen også kan påvirke korrosjo nsbestandigheten vil alle faktorers påvirkning undersøkes både isolert og samlet i systematisk rekkefølge. The main purpose in this project is to investigate the properties of alloy EN 1982 in the presence of a strong magnetic field while submerged in seawater. The core of the research is to investigate how the magnetic field may influence the built-up and break down of the protective oxide film that normally develops on the surface of this material when exposed to seawater. The nature of this oxid e layer determines the alloys resistance to corrosion, and is therefore decisive for the alloys performance in seawater. The supposed effect a magnetic field has on the built up and break down of the alloys oxide layer will be investigated by extensive co rrosion experiments in seawater laboratories, under the influence of a strong magnetic field. Because other factors, such as pollution in seawater, cathodic protection and microstructure of the alloy might also influence the corrosion pro perties of the alloy, all these factors will also be investigated, both separately and togehter in a systematic order.