Abstract
The effect of the additive dibutyl thiourea (DBTU) on the corrosion of 70Cu–30Ni alloy and of carbon steels in HCl solutions in distilled water and in sea water at pH 1·8–2·0 was observed using the weight loss technique at temperatures between 19 and 60°C. In the absence of DBTU the corrosion of the Cu–Ni alloy is characterised by an induction period which is longer in the pure acid than in acidified sea water. Following the induction periods, the loss in weight varies linearly with time and is temperature dependent in the pure acid, but not in sea water. On the other hand, the weight loss of carbon steel in both media varies linearly with time directly from the moment of immersion. The rate of dissolution in pure HCl is greater than in acidified sea water and both are temperature dependent. The effect of concentration of DBTU on the dissolution of the two alloys in both media was tested at 60°C. In all cases inhibition of corrosion increased with additive content. The inhibition efficiencies in presence of 300 ppm DBTU amounted to 78 and 30% for Cu–Ni and 87 and 75% for carbon steel in pure HCl and acidified sea water, respectively. Weight loss experiments carried out under modified conditions suggested decomposition of DBTU when in contact with the metal surface. The results of the present investigation reveal that DBTU is not a particularly effective inhibitor for the acid washing of multistage flash distillation units.
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