Corrosion characteristics of fatty acids in water solutions

[摘要] The main investigation consisted of determining corrosion rates of mild steel(A lSI 1 020) exposed to de-aerated stagnant solutions of fatty acids in waterat different acid numbers and temperatures, with the aid of mass loss tests.The temperature range investigated varied from 25°C to 250°C. Resultsshowed that corrosion rates initially increased with temperature and atcertain elevated temperatures thick multi-laminated corrosion product filmsformed on the specimen surfaces which .led to decreases in corrosion rateswith further increases in temperature. Corrosion product films influenced thecontrol mechanism of the corrosion process and it was seen that thecharacteristics of these films were dependent on the temperature as well asfatty acid type. The acid number range investigated was from 0 to 25 mgKOH/g solution. Corrosion rates increased with an increase in acid numberirrespective of the control mechanism. Results indicated that the corrosivityof acid solutions decreased with an increase in chain length of the organicacid molecule, when no corrosion product films were present. The presenceof corrosion product films rendered complex relationships.Electrochemical tests were done on specific fatty acid systems at 25 °C.Corrosion rates evaluated from electrochemical observations correlated wellwith mass loss results and it was concluded that the corrosion mechanismwas electrochemical.Supplementary investigations were conducted on specific fatty acid systemsand included the following:Turbulence did not influence the corrosion process. This is typical for anactivation-controlled system where no corrosion product films are presenton the specimen surfaces. Mixing of acids showed a corrosion rate of approximately an average of thetwo individual corrosion rates of the pure systems.Monitoring studies showed that results obtained with the Corrator correlatedbetter with mass loss and electrochemical corrosion rates than Corrosometerresults.Corrosion rates increased with an increase in dissolved oxygen content levelof the solution and with additions of chloride, but sulphur additions renderedlower corrosion rates.A water phase process stream received from SASOL showed that thecorrosion rate increased with temperature and levelled out towards 200°CThe corrosion characteristics of the received stream can be simulated byacetic acid with the same acid number.

[发布机构] University of Pretoria