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The Corrosion Performance of Galvanized Steel in Closed Rusty Seawater

DOI: 10.1155/2013/267353

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The corrosion performance of galvanized steel in closed rusty seawater (CRS) was investigated using weight loss, Tafel polarization curve, and electrochemical impedance spectroscopy. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were carried out for morphological and chemical characterization of the rust layer absorbed on the zinc coating. Effects of temperature and hydrostatic pressure on corrosion resistance of galvanized steel were studied. Results indicated that rust layer could induce pitting corrosion on the zinc coating under the Cl? erosion; high temperature accelerated the corrosion rate of zinc coating and inhibited the absorption of rust layer; the polarization resistance ( ) of galvanized steel increased with the increase of hydrostatic pressure in CRS. 1. Introduction The PVC encapsulated galvanized steel wire is widely applied in submarine cable project in recent years [1]. PVC is coated on the surface of galvanized steel by thermal compression. This PVC coating can prevent the penetration of seawater and air and then inhibit the corrosion of galvanized steel. However, the failure of PVC will result in the penetration of seawater with immersion time, and the initial rust layer produced on the surface of the galvanized steel cannot fall off because the coating of PVC. Thus, the galvanized steel was always immersed in a closed saturated rusty seawater environment (Figure 1). Figure 1: Schematic diagram of galvanized steels coated by PVC: (a) the failure zone of the PVC coating, (b) the corroded surface of the galvanized steel. It is acknowledged that when galvanized steel is exposed to marine environment, the main corrosion products (Zn5(OH)2Cl8) have been found in longer exposure periods [2, 3]. When the galvanized steel is coated by PVC and used as cables in seawater, the corrosion performance of galvanized steel under this closed rusty seawater (CRS) is primary in the process of metallic corrosion [4, 5]. It is expected that the corrosion performance of galvanized steel may be different since the rust layer affects corrosion-related processes, such as the mass transport of dissolved oxygen [6, 7], the stability of the passive film, and the hydration of the dissolved metal ions [8–10]. There are few reports regarding the corrosion behavior of galvanized steel under closed rusty seawater environment. In our previous works, it had been demonstrated that Cl? concentration and pH have very important effects on corrosion behavior of galvanized steel under simulated rust layer solution [11, 12]. In the present work,

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