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Work In The Sea
Published in Robert A. Ragotzkie, J. Robert Moore, Man and the Marine Environment, 2018
Protection against corrosion is a highly complex technology and involves divers at several levels. Their work is mainly in the installation of anodes and protective coatings, and in the cleaning and inspection of completed structures. Corrosion of steel in saltwater is an electrochemical process and it can be combatted rather effectively by means of applied electrochemistry, either by imposing appropriate currents counter to the corrosive action, or by means of sacrificial anodes. A sacrificial anode is made of a metal which has an electrochemical potential such that it will be attacked and corroded away before the steel structure. Zinc is the most practical for use on steel, and zinc anodes are placed on many structures. They are usually bolted to flanges which are welded to the structure; when necessary the anodes are replaced by rebolting or rewelding. In any case this job is invariably done by divers. Corrosion is often more of a problem near the surface, and a typical diver’s job is to apply an epoxy coating to the “splash zone” of a structure. Corrosion is also much greater when the pipe is heated by the oil.
Mechanism of Corrosion
Published in Harry J. Meigh, Cast and Wrought Aluminium Bronzes, 2018
The more rapidly the anodic metal is attacked, the more the nobler metal is protected by the deposit of ions. This is the reason for the use of a ‘sacrificial anode’ to protect an expensive material from corrosion. A sacrificial anode is a lump of inexpensive metal which, as the term indicates, is anodic to the metal to be protected. It is connected to the nobler metal and immersed in the same medium where it corrodes and protects the nobler metal from corrosion as explained above. It is standard practice on offshore oil rigs to fit sacrificial anodes that are designed to be replaced during major maintenance and, in some cases, to last the life of a rig.
Amorphous silicon nanotubes
Published in Klaus D. Sattler, Silicon Nanomaterials Sourcebook, 2017
Mirko Battaglia, Salvatore Piazza, Carmelo Sunseri, Rosalinda Inguanta
For a given displacement reaction, the choosing of the anode material is principally associated to the desired driving force. The most common materials used as sacrificial anodes are zinc, aluminum, and magnesium. Among these three materials, the thermodynamic driving force is the highest for magnesium, the lowest for zinc. In any case, care must be taken in avoiding the passivating conditions of the sacrificial anode. From this point of view, aluminum is the material at the highest risk of being covered by a nonconductive passivating film, even if it holds a great attraction due to its very low electrochemical standard potential and facile handling.
Effect of cathodic protection methods on ferrous engineering materials under corrosive wear conditions
Published in Corrosion Engineering, Science and Technology, 2020
F. Brownlie, L. Giourntas, T. Hodgkiess, I. Palmeira, O. Odutayo, A. M. Galloway, A. Pearson
An alternative cathodic protection methodology is SACP, in which a metallic alloy, which is more active than that of the protected metal alloy, is utilised to create a galvanic cell. Therefore, the current is supplied by the preferential corrosion of the more active metal called a sacrificial anode. Common materials used as sacrificial anodes for the protection of steels are zinc-based alloys, aluminium-based alloys and magnesium-based alloys [12]. The advantages of using sacrificial anodes are as follows: easy installation, inexpensive maintenance and low capital cost. The main disadvantages of using sacrificial anodes are that periodic replacement of the anodes during scheduled maintenance may be required and the galvanic current available is dependent on the sacrificial anode area [14].
Corrosion effect of ferrous metals on degradation and remaining service life of infrastructure using pipe fracture as example
Published in Structure and Infrastructure Engineering, 2020
Chun-Qing Li, Wei Yang, Wenhai Shi
The effect of soil properties, in particular, the acidity, as measured by pH, and saturation, as measured by moisture content, on corrosion as measured by mass loss is shown in Figure 11. As can be seen, the high corrosion, i.e. mass loss, was obtained from the high saturated and high acidic soil for a short exposure of 180 days because of de-passivation of the specimen surface. However, after 545 days, the maximum corrosion was seen in the least acidic batch of 5 pH from both measurements. These results have practical applications in corrosion protection of underground infrastructure using cathodic protection or sacrificial anode. The results suggest that old pipelines which are buried in less acidic saturated soil conditions, such as 5 pH, are more prone to corrosion failures than those in the high acidic conditions (2.5 pH). The results of the coupled effect of varying acidity (2.5, 3.5 and 5 pH) with high saturation (80%) can be used as a benchmark for estimating accurate corrosion rates in the field, assisting the repair and maintenance time for a given type of soil conditions.
The fate and enhanced removal of polycyclic aromatic hydrocarbons in wastewater and sludge treatment system: A review
Published in Critical Reviews in Environmental Science and Technology, 2019
Xiaoyang Zhang, Tong Yu, Xu Li, Junqin Yao, Weiguo Liu, Shunli Chang, Yinguang Chen
Electrocoagulation (EC) is a typical type of electrochemical oxidation, which removes organic pollutants not only by the redox reaction but also by coagulation and flotation (Katal & Pahlavanzadeh, 2011; Ugurlu, Gurses, Dogar, & Yalcin, 2008). Generally, iron and aluminum are used as sacrificial anode. In the EC process metal hydroxides (such as Al(OH)3, Fe(OH)2 and Fe(OH)3) are formed, which can act as coagulation and flotation reagents and therefore promotes the elimination of PAHs (Hua, Huang, Su, Tran-Ngoc-Phu, & Chen, 2015; Mollah et al., 2004). As hydrogen and oxygen bubbles are generated in the cathode and anode, it contributes to the flotation or stripping of volatile pollutants from water into the air (Ugurlu et al., 2008). Electrocoagulation technique has been reported to be effective in removal of PAHs from the effluent of a paper-making wastewater (Gong et al., 2017).