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Coatings 2017, 7(4), 52; doi:10.3390/coatings7040052

The Effect of Temperature and Local pH on Calcareous Deposit Formation in Damaged Thermal Spray Aluminum (TSA) Coatings and Its Implication on Corrosion Mitigation of Offshore Steel Structures

1
School of Engineering, Federal University of Rio Grande do Sul, Porto Alegre 90040-060, Brazil
2
TWI Ltd., Cambridge, CB21 6 AL, UK
*
Author to whom correspondence should be addressed.
Academic Editors: Niteen Jadhav and Andrew J. Vreugdenhil
Received: 2 December 2016 / Revised: 3 April 2017 / Accepted: 5 April 2017 / Published: 11 April 2017
(This article belongs to the Special Issue Coatings for Corrosion Mitigation)
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Abstract

This paper is based on experimental data and provides better understanding of the mechanism of calcareous deposit formation on cathodically polarized steel surfaces exposed to synthetic seawater at 30 °C and 60 °C. The study comprises measurement of the interfacial pH of thermally sprayed aluminum (TSA) coated steel samples with and without a holiday (exposing 20% of the surface area). Tests were conducted at the corrosion potential for up to 350 h. It was experimentally determined that the local pH adjacent to the steel surface in the holiday region reached a maximum of 10.19 and 9.54 at 30 °C and 60 °C, respectively, before stabilizing at about 8.8 and 7.9 at the two temperatures. The interfacial pH on the TSA coating at 30 °C was initially 7.74 dropping to 4.76 in 220 h, while at 60 °C it increased from pH 6.41 to the range pH 7.0–8.5. The interfacial pH governed the deposition of brucite and aragonite from seawater on the steel surface cathodically polarized by the TSA. This mechanism is likely to affect the performance of TSA-coated offshore steel structures, especially when damaged in service. View Full-Text
Keywords: pH; thermally sprayed aluminum (TSA); offshore pH; thermally sprayed aluminum (TSA); offshore
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Ce, N.; Paul, S. The Effect of Temperature and Local pH on Calcareous Deposit Formation in Damaged Thermal Spray Aluminum (TSA) Coatings and Its Implication on Corrosion Mitigation of Offshore Steel Structures. Coatings 2017, 7, 52.

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