Painting ship hulls

Aluminum and aluminum-zinc alloy anodes have become the preferred sacrificial anodes for the cathodic protection of offshore platforms. This preference is because aluminum anodes demonstrate reliable long-term performance when compared with magnesium, which might be consumed before the platform has served its useful hfe. Aluminum also has better current/weight characteristics than zinc. Weight can be a major consideration for large offshore platforms. The major disadvantage of aluminum for some applications, for example, the protection of painted ship hulls, is that aluminum is too corrosion resistant in many environments. Aluminum alloys will not corrode reliably onshore or in freshwater [37]. In marine... 

Boron carbide Pine (Pinus palustris) tar paints, reodorant a-Terpineol paints, roofing Montan wax paints, semidrying oil Corn (Zea mays) oil paints, ship hulls Ferric oxide paints, special Asphalt... 

The domain under consideration (electrolytic domain) may also be infinite. This is clearly the case in marine applications. A fictitious two-dimensional version of this situation is displayed in Fig. 8. Here, the structure to be protected is the well-painted ship hull but with bare areas (cathode) being present. The hull is to be protected with anodic sections. The governing partial differential equation and the associated boundary conditions are depicted in the schematic. In the case of an infinite electrolyte, two auxiliary constraints are included. The behavior of the far-field potential (poo is given by (16) ... 

The most significant chemical property of zinc is its high reduction potential. Zinc, which is above iron in the electromotive series, displaces iron ions from solution and prevents dissolution of the iron. For this reason, zinc is used extensively in coating steel, eg, by galvanizing and in zinc dust paints, and as a sacrificial anode in protecting pipelines, ship hulls, etc. 

U.S. MiHtary Specification DOD-P-24647, Paint, Antifouling, Ship Hull, Mat. 22, 1985. 

The outstanding virtue of zinc-rich paints is simplicity in application. No special equipment is required and the operation can, of course, be carried out on site, large or small structures being equally suitable for treatment. While there is some evidence that the zinc-rich paints will reduce iron oxides remaining on the steel surface, proper surface preparation is as important here as with traditional paints if the best results are to be achieved. The main use of zinc-rich paints is to protect structural steel-work, ships hulls, and vulnerable parts of car bodies, and to repair damage to other zinc coatings. 

The total paint system of a typical underwater ship hull is shown in Figure 6. 

Protective Coatings. A variety of protective coatings is available for steel in sea-water service. For such applications as ships hulls, normal practice is to apply compatible antifouling paint over the corrosion-resistant primer coating system. Figure 4 shows panels which have resisted fouling for a year or more as compared with adjacent panels where the experimental coating is not protective. 

Me>,NC(Sj- H NO Additives for anti-foulmg paint protecting ship hulls 196. 545... 

Cathodic protection has many applications, e.g. in refineries, power stations, gas, water, and oil utilities on marine structures, e.g. jetties, piers, locks, offshore platforms, pipelines, ships hulls, etc. and on land structures, e.g. buried pipeline, storage tanks, cables, etc. For each use, the cathodic protection system requires careful design, either impressed current, sacrificial anodes, or a combination of both may be chosen. There may also be other protection systems, e.g. paint, the nature of which will affect the design parameters and must be taken into consideration. 

USE As pigment for rubber, paints, paper, linoleum, ceramics, glass in paint for ironwork, ship hulls as polishing agent for glass, precious metals, diamonds in electrical resistors and semiconductors in magnets, magnetic tapes as catalyst colloidal solns as stain for polysaccharides. 

Callow [1990] has described the use of antifouling paints in conjunction with ships hulls to reduce microbial and macro-fouling, but the principle could be applied to heat exchangers in suitable environments. She defines three major types of antifouling paints. 

In the soluble matrix type cuprous oxide and sometimes other biocides, is incorporated into a resin binder. The acidic resin slowly reacts with the sea water (pH approximately 8.0) and dissolves continuously exposing the cuprous oxide particles that are gradually released at the water/solid interface. The newly created surface provides antifouling properties. Depending on thickness the life of these paints on ships hulls, in contact with sea water, is 1 - 2 years. 

Although trace amounts of copper are essential for life, copper in large amounts is quite toxic copper salts are used to kill bacteria, fungi, and algae. For example, paints containing copper are used on ship hulls to prevent fouling by marine organisms. 

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