Coatings In Seawater Research Articles

A mathematical model for lifetime prediction of lacquer‐paint coatings in sea water

AbstractMain features of the mechanism of lacquer‐paint coatings destruction in sea water have been revealed. On this basis, a mathematical model has been developed and boundary value problems of mathematical physics have been formulated to calculate the determining processes on characteristic stages of coatings in sea water. The theoretical evaluation of coatings longevity depending on physical characteristics of the system has been made. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Corrosion resistance of steel with hot‐dipped galvanized zinc and zinc alloy coatings in seawater

AbstractHot‐dipped galvanized zinc and zinc alloy coatings were used as protective metallic coatings for steel structures in seawater in China. Corrosion of the two coatings immersed in sea water in Qingdao and Xiamen for 6 years were introduced and analyzed, which provides a basis for further development and applications of these coatings in China. Tests proved that the anti‐corrosion performance of the hot‐dipped low alloy zinc coatings (aluminum content less than or equal to 10 wt%) is equal to or even lower than that of the pure zinc sheet, while the performance of the hot‐dipped high alloy zinc coatings is higher than that of the pure zinc sheet. The hot‐dipped high alloy zinc coatings can be further developed for optimal performance in the future.

Microstructure and Corrosion Resistance of HVOF Sprayed 316L Stainless Steel and Hastelloy C Coatings

In order to develop dense corrosion resistant coatings by thermal spraying, 316L stainless steel and Hastelloy C alloy powders were sprayed by an HVOF thermal spraying apparatus onto a mild steel substrate. The microstructure, pore size distribution, composition and corrosion resistance of the obtained coatings were evaluated experimentally. Corrosion resistance in seawater was examined by monitoring the impedance and corrosion potential of samples immersed in artificial seawater at 300 K over a period of more than 3 months and also by polarization measurement. It was found that the stainless steel coatings composed mainly of plastically deformed particles and some splats that were molten at the impact. By increasing the combustion pressure, the porosity measured by a mercury porosimeter was reduced to below 1%. In comparison, Hastelloy C deposits sprayed under a standard condition were so dense that their porosity could not be measured by the porosimeter. The polarization curves and the results of impedance monitoring exemplified that the Hastelloy C coatings possess much superior corrosion resistance to the stainless steel coatings in seawater, which was attributed mainly to the higher density and better adhesion of the Ni-base alloy coatings.

Mathematical modelling of ageing and lifetime prediction of lacquer-paint coatings in sea water

The mathematical model based on the physical ideas of the processes in the system sea water–coating–metal base helps to describe these processes on the selected definite stages of coatings exploitation up to their cohesive or adhesive destruction. For each of these stages, the appropriate linear or nonlinear problems of mathematical physics have been formulated, and the procedure of their solution has been elaborated. The model will allow us not only to predict the lifetime of coatings, but to optimise the parameters of newly constructed coatings with the aim of increasing their durability.

Investigation of contact corrosion of anodic coatings depending on the type of polarization of materials of the base and coating

We propose a refined mathematical model for the fracture mechanism and prediction of durability of anodic coatings in seawater. Various types of polarization of materials of a coating and a base in electrolyte are considered. We investigate the influence of the thickness of electrolyte on fracture of anodic coatings. The results of the quantitative investigations performed enable us to propose certain recommendations concerning the optimal choice of the material of a coating depending on the geometric sizes of possible through damages in it. For noninteracting small strips-damages, we established the existence of a critical thickness of the electrolyte, for which the density of the corrosion current increased by 30–35%.

Mathematical description and analysis of the corrosion of metals under lacquer coatings in seawater

We propose a mathematical model for the analytic investigation of the processes of corrosion fracture of metals under lacquer coatings in seawater on the basis of an experimentally established dependence of the corrosion rate of a metal without coatings on the concentration of a passivator. It is shown that, for the examined type of coatings, the corrosion rate first linearly increases with time but then, on attainment of a certain level, its subsequent increase is substantially decelerated. If the corrosion rate of the uncoated metal is higher than 0.05 mm/yr, then the rate of corrosion under coatings is lower by at least an order of magnitude.

Performance and effectiveness of non‐stick coatings in seawater

Several non‐stick coatings mainly based on silicones were tested under laboratory and field conditions in regard to their toxicity and their influence on the settlement of cyprid larvae (Balanus amphitrite). The toxicity was very low for most of the coatings. The antifouling properties were evaluated in exposure trials over 6 months at several stations along the German coast. The field trials were performed by stationary exposure and with periodically moved catamarans. The silicon coatings exhibited the best performance and 4 out of 9 of these were highly effective. The adhesion force of barnacles on silicones was substantially reduced in relation to control substrata. The leaching of organotin compounds derived from some of the silicone coatings used was less than, or in the range of, the induction leaching‐rates found in organotin‐stabilized Formica tubes.

A method for testing the mechanical strength and kinetic features of fracture of lacquer coatings in seawater

A method for testing lacquer coatings in seawater is developed. This method enables one to predict the cohesion and adhesion strength of these coatings under conditions close to operating. The mechanical strength of the coatings is estimated with the help of a dimensionless parameter. Within the framework of the proposed testing method, one can also investigate the kinetic properties and other characteristics of fracture of lacquer coatings by using an optical technique and photography.

Blistering Mechanisms of Thermally Sprayed Zinc and Zinc-Based Coatings in Seawater

Abstract This work is concerned with the blistering mechanisms of thermally sprayed zinc or Zn-Al alloy metallic coatings on the aluminium alloy 5086 in seawater. It was found that the blistering w...

Anticorrosion coatings for equipment and pipelines of desalting plants

This study deals with the basic principles of enhancing the durability of anticorrosion coatings in sea water at elevated temperatures. It contains the results of laboratory, full-scale field and production tests of some existing systems of anticorrosion polymer coatings, and some recommendations for the use of these polymer coatings in desalting plants for protection of their equipment and pipelines.

A.C. impedance measurements on marine paint systems

The breakdown of three marine paint coatings in seawater has been followed with a prototype simplified A.C. Impedance instrument with a frequency range 10 kHz to 5 Hz and impedance range switchable from 5 Ω to 10 MΩ. From the results obtained it is thought that simpler dedicated instruments could be developed, but for on-site measurements on submerged structures there are complications in isolating the area of paint film under test from the remainder of the structure.

Effect of alloying additions on the structure and corrosion properties of zinc coatings

Prolonged corrosion tests in a stream of sea water on samples galvanized in baths with different alloying additions showed that the corrosion resistance of zinc coatings in sea water can be improved by alloying with 0.01% Ti+0.05% Mg+0.1% Al and with 0.01% Ti.