Materials Performance

MAY 2017

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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36 MAY 2017 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 56, NO. 5 COATINGS & LININGS W Corrosion behaviors of high-velocity, arc-sprayed aluminum coatings at high hydrostatic pressure were evalu- ated in a simulated deep sea environ- ment, using microstructures analysis, rust composition analysis, electro- chemical measurements, scanning electron microscopy, x-ray diffraction analysis, and Fourier transform infra- red spectra analysis. This last analysis concluded that corrosion products at 30 atm were mostly basic aluminum chloride, with low cohesion and can easily dissolve in a sodium chloride (NaCl) solution, resulting in rapid fail- ure of Al coatings. Meanwhile, poten- tiodynamic polarization curves indi- cate that high pressure increases self-corrosion current density of Al coatings. With the rapid development of deep sea en g in e erin g, m any inv e sti gators h av e started to pay attention to the problem of engineering material corrosion. However, corrosion mechanisms of materials in deep sea environments are quite different from those in a shallow sea, so the problems of deep sea corrosion must be considered separately. A few studies have focused on corrosion behaviors of materials in deep sea environ- ments since the 1960s. 1-4 Some investiga- tors exposed materials in the deep sea to study their corrosion mechanisms. Ven- katesan 5 found that the corrosion rates of Al alloys 1060 and 2000 (UNS A91060 and N06200) increase with increasing water depth, but the concept that all other mate- rials will follow this behavior is unsubstan- tiated. For instance, Reinhart, et al. 6-7 inves- tigated the corrosion behaviors of nickel in 760- and 2,100-m water depths. That test- ing revealed that corrosion rates decrease with water depth. Although investigators may obtain some inferences in the real environment, they cannot entirely under- stand how the environmental parameters inf luence corrosion processes. Therefore, other researchers carried out a series of simulated experiments in order to simplify experimental conditions. 8-9 For instance, Zhang, et al. 10 investigated the corrosion mechanisms of Fe-20Cr steel at high hydro- static pressure (HP), which showed that HP can increase pitting sensitivity. Liu, et al. 11 found that different steels exhibit different corrosion behaviors; for example, at high HP, localized corrosion with shallow dish shapes appeared on 10NiCrCuNbTi steel surfaces, and localized corrosion with tun- nels appeared on 06NiCrVMo steel sur- faces. Dif ferent materials have specific characteristics at high HP, so it is necessary to individually research th e corrosion behaviors of common marine materials. High-velocity, arc-sprayed Al coatings, because of excellent corrosion resistance, are used to protect steel substrates, which are components in large steel structures such as bridges, derricks, and ships. Al coatings can provide anodic sacrificial pro- tection for steels in moist air and seawater. Meanwhile, Al passive films can grow on Al- coated surfaces, which can protect the Al coatings from oxygen corrosion. 12 To date, most research of Al coatings has focused on the corrosion behaviors in shallow sea envi- Effect of High Hydrostatic Pressure on Aluminum Coatings t ong Hui, Han Wenli, Xu Z H ongping, Z H ang Yanjun, and l in Z H u, CNPC Research Institute of Engineering Technology, Tianjin, P.R. China Wei s H ic H eng and Xu Bins H i, National Key Laboratory for Remanufacturing, Academy of Armored Forces Engineering, Beijing, P.R. China

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