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Title: Durability studies relevant to marine equipment
Author: Mantzavinos, Dimitris
ISNI:       0000 0001 3618 5404
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 2001
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The corrosion behaviour of two copper-nickel alloys, namely Cu-30%Ni and Cu- 10%Ni, commercially pure titanium and two titanium alloys (T1-6A1-4V and Ti:5111) has been examined in environments of relevance to desalination and other marine equipment. The investigation was focused on two extremes of environments, pure water and high-velocity (with and without suspended solids) saline water. These represent conditions in which operational problems have been experienced or are anticipated and in relation to which very little information on basic durability is available. This work contained only brief experiments in quiescent seawater which has been studied in abundance previously; such tests were included in this research for background and comparison purposes only. The study involved exposure of specimens to distilled water (1.5-7 μS/cm) at 20°-80°C with and without injected carbon dioxide. At 20°C upon initial exposure to distilled water, the 10%Ni alloy exhibited somewhat active corrosion behaviour during anodic polarisation potentiodynamic scans, but after a few days' exposure, more passive behaviour of both alloys was indicated with the 30%Ni material demonstrating better corrosion resistance than the lower-nickel alloy. This relative behaviour was replicated in comparative tests conducted in 3.5% NaCl at 20°C in which the corrosion resistance of Cu-30%Ni was clearly greater than that displayed by the lower-Ni alloy. However, at higher temperatures in distilled water, the superiority of the 30%Ni alloy was less evident especially in the presence of dissolved carbon dioxide. Microscopical examination of specimens revealed a susceptibility to general corrosion with 'etched' surfaces and also pitting attack which seemed to have a lesser effect on Cu-10%Ni than Cu-30%Ni. Certainly at short exposure times, titanium, titanium alloys and UNS S31603 stainless steel (used for comparison purposes) exhibited considerably superior corrosion resistance than the copper-nickel alloys over the entire range of distilled water conditions studied. The erosion-corrosion characteristics of commercially pure titanium, the two titanium alloys, UNS S32760 and UNS S31603 stainless steels were assessed under an impinging jet of 3.5% NaCl solution at a velocity of 71.1 m/s free from solids at both 20° and 50°C, and also at a velocity of 12.6 m/s containing solids up to 1800 ppm at 20°C. Under zero-solid liquid erosion-corrosion conditions at 20°C, UNS S31603 stainless steel and the three Ti-base materials exhibited excellent erosion-corrosion resistance. At 50°C UNS S31603 stainless steel showed some weight loss but the Ti-base materials retained their excellent erosion-corrosion resistance. After anodic polarisation tests in zero-solid liquid erosion-corrosion at 20°C, the three Ti-base materials were covered rather evenly by films of various thicknesses, apparently formed due to hydrodynamic effects. That was also the case for zero-solid liquid erosion-corrosion tests at 50°C with and without polarisation. In the presence of solids, all the materials suffered some deterioration. Quite interestingly, in terms of material loss, pure titanium's erosion-corrosion resistance was found to be no better than the one exhibited by UNS S32760 stainless steel. The relative contribution to overall erosion-corrosion damage, from pure erosion, pure corrosion and interactive synergistic processes were quantified and some complex features of the disposition and mechanisms of erosion-corrosion became apparent through tests on concentric specimens. Microscopical examination after solid/liquid erosion-corrosion tests revealed drill holes in the centre of the specimens (region directly under the jet) and signs of plastic deformation ('skid' marks) further out for all four materials. UNS S31603 also showed evidence of damage due to pitting attack. In terms of the mechanisms of attack by the contributory processes, whilst the detailed mechanisms of the synergistic component was not unambiguously identified, it was clearly evident that the pure corrosion component of the erosion-corrosion deterioration involves rapid periodic depassivation/repassivation events. The pure erosion damage was observed to be associated with microdrilling and plastic deformation processes.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Corrosion behaviour