Purpose
– This paper aims to determine the effect of water on the SCC of low carbon steel in ethanol in the absence of supporting salts.
Design/methodology/approach
– Slow strain rate test was done to determine SCC susceptibility. Fractured samples were examined using optical microscopy and scanning electron microscopy.
Findings
– While the results demonstrated that water alone had no effect on the SCC susceptibility of low carbon steel in ethanol, 2.5 volume per cent moisture gave indications of cracking tendencies.
Originality/value
– With South Africa and the world over turning to bioethanol and ethanol blended fuels as a means of reducing its carbon foot print, there are concerns over the corrosive nature of ethanol on common engineering metals like low carbon steels.
AISI 304L stainless steel was laser surface alloyed with ruthenium enriched 304L powder using a continuous wave Nd:YAG laser. Corrosion performance of the surface alloys was studied in 1 M sulphuric acid and 3.5 wt% sodium chloride at 25, 35 and 45 °C using potentiodynamic polarisation. The results showed that the presence of ruthenium decreased corrosion rates in both solutions and inhibited pitting in sodium chloride. High temperatures were particularly detrimental to the corrosion resistance of the alloys in sodium chloride, but were surprisingly beneficial in sulphuric acid; inducing spontaneous passivity and reducing corrosion current density from 129 μA/cm2 at 25 °C to about 0.5 μA/cm2 at 45 °C.
Corrosion resistance of stainless steels is significantly compromised in oxygen-deficient environments, leading to limited service life as well as unsatisfactory performance of the structures made of these alloys. Cathodic modification with ruthenium has been demonstrated to remarkably improve the corrosion resistance of stainless steels in reducing acidic media, even in the presence of an abrasive suspension. Although ruthenium is several times cheaper than other platinum group metals (PGMs), alloying with ruthenium remains prohibitively more expensive than alloying with conventional, although less effective, metals. A number of strategies have been explored to reduce the amount of ruthenium required to cathodically modify stainless steels in a bid to make this cheaper option much cheaper and thus increase the cost-benefits of using these alloys. Some of the strategies include partially substituting ruthenium with cheaper metals, as well as introducing the PGM as a surface alloy.
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