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In the oil and gas industry, thermally sprayed aluminum (TSA) coatings are commonly used, primarily, to reduce anode demand in cathodic protection systems and impart some degree of sacrificial protection in the topsides and splash zone areas. The use of TSA coatings has advantages in systems where long service life is required. TSA coatings are also used to reduce the formation of calcareous deposits, normally a combination of CaCO3 and Mg(OH)2, on heat exchanger piping.
The formation of calcareous deposits on thermally sprayed aluminum(TSA)-coated surfaces immersed in natural seawater and connected to a cathodic protection system is a recurring issue. Calcareous deposition has occurred even though TSA coatings have a lower cathodic over potential compared with carbon and stainless steels, which should reduce the thermodynamic precipitation driving force. There is at present limited knowledge on the calcareous deposits’ formation kinetics on TSA in natural seawater following prolonged exposure at different temperatures. In this study, bare 25Cr super duplex stainless steel (SDSS) and TSA-coated SDSS samples (with and without an silicone-based sealer) were exposed to natural seawater under potentiostatic cathodic protection (CP) and open circuit potential (OCP) conditions at different temperatures (i.e., 20, 35, 60 and 80°C) for 1.5 years. Samples were extracted at various intervals to construct growth kinetics curves under the various test conditions. The deposits were subsequently examined using scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Lastly, recommended CP protection potentials and current density values were obtained based on the findings of this study.
This paper provides an overview of the electrochemical passivation process, history of the BurlingtonSkyway, description of the installation process, treatment results and up to 30 years of monitoringresults for the structure.
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Impressed current rectifiers are the backbone of a pipeline operator’s cathodic protection (CP) systems. A rectifier’s ability to protect a large length of electrically continuous pipeline considerably improves efficiencies and reduces material costs as compared to galvanic systems. However, like galvanic anodes, impressed current anodes are a consumable asset, and require replacement at the end of their service life to ensure that the rectifier can continue to adequately protect the pipeline.
Galvanized protective coatings have been used for structural steel to mitigate steel corrosion in atmospheric exposures and chloride-rich marine environments. The galvanizing process involves dipping steel elements free of surface mill scale in a molten zinc bath where the diffusion of zinc into the steel matrix allows for zinc-iron alloy layers of decreasing zinc concentrations by depth to form in the steel. Oher elements such as tin, antimony and aluminum may be added to the galvanizing bath to control reaction rates, surface appearance and corrosion behavior. Hot-dipped galvanizing provides corrosion protection by developing a barrier layer and in certain conditions provide beneficial galvanic coupling of the zinc-rich layers to the steel.