Arrangement of Anodes

The rudder is provided with anodes on both sides these should be fixed either at the level of the propeller hub or as far as possible above and below on the rudder blade. There are specially shaped mdder anodes which are welded to the front edge of the mdder. Sea chests and scoop openings should be specially considered and provided with anodes because of their increased current requirement. 

For partial protection of the stem, 33% of the Miodes used for complete protection should be installed instead of the usual 25%. Of these, 25% serve as actual protection for the stem and 8% as shielding for the stem area against the remainder of the current-consuming body of the ship. These anodes are known as gathering anodes and are fixed in front of the anodes protecting the stem. 

Propeller brackets in multipropeller ships must be particularly protected. In small ships the anodes are attached on both sides at the base of the propeller bracket. With large ships the anodes are welded onto the propeller brackets (see Fig. 17-4). 

Shafts and screws should also be included in cathodic protection with galvanic anodes and shaft slip rings. The transmission voltages should be below 40 mV (see Section 17.3.3.3). 

Special propulsion also requires relevant calculations and distribution of the anodes. For Kort nozzles, the total surface area of the rudder is determined and a basic protection current density of 25 mAm imposed. The anodes are attached on the external surface at a spacing of 0.1 r to 0.25 r at the region of greatest diameter. Internally the anodes are fixed to the strengthening stmts. With Voith-Schneider propellers, the anodes are arranged around the edge of the base of the propeller. 

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The arrangement of anodes for introducing a protection current with tank farms consisting of flat-bottomed tanks can be carried out as follows [15] ... 

Fig. 17-9 Example of the arrangement of anodes and reference electrodes from Ref. 13.

Fig. 21-2 Arrangement of anodes in the entry chamber of a power station condenser.

Masuda H, Hasegwa F, Ono S (1997) Self-ordering of cell arrangement of anodic porous alumina formed in sulfuric acid solution. J Electrochem Soc 144 L127-L130... 

Figure 4.5.19 depicts the schematics of the mercury cell anodes with an expanded titanium mesh [109]. Other types of mercury cell anodes use small diameter titanium rods or thin titanium blades. Electrical connection in the ceil is made through the boss using solid copper rods protected with a riser tube of titanium. A typical arrangement of anodes in a mercury cell is shown in Fig. 4.5.20. 

While, in both types of reactor, it is desirable to maximize the surface area per unit volume, the designer of an electrolytic cell has to concern himself with the problems of non-uniform current distributions, since the electrode surface will only be active if there is an appropriate local potential difference it was noted above that the geometric arrangement of anode and cathode is the key factor. 

Figure 12-2 shows as an example the arrangement of the anode installation for the local cathodic protection of pipelines in a power station. The cooling water pipelines have a nominal diameter of DN 2000 and 2500 and a covering of earth up to 6 m. The fire-fighting pipelines have a nominal diameter of DN 100 and a covering of 1 m. All the pipelines have a bitumen coating. 

The required number, n, of anodes can be calculated using Eq. (17-2) from the current requirement, together with the maximum current output 1 of the anodes. The arrangement of the anodes is dealt with in Section 17.3.2.2. Galvanic protection systems are usually designed to give protection for 2-4 years. After this period, a maximum of up to 80% of the anodes should be consumed. 

Nonuniform current and potential distribution is usually to be expected with uncoated objects to be protected. The distribution can be considerably improved by coatings (see Section 20.1.3). In enamelled tanks, the current and potential distribution of cathodic protection is very good. By arranging the anode centrally, IR errors from equalizing currents in the switching-off phase can be ignored. The anode potential in the switching-off phase can be evaluated from the information... 

Figure 20-12 shows schematically the arrangement of aluminum anodes in vertical and horizontal boilers with heating tubes. More than 33% of the aluminum anodes must be sited in the upper third of the tank for the formation of protective films in the tubing [18], Cathodic currents needed to protect the tubing may be three times as high as the current requirement for cathodic protection [19]. 

The arrangement and distribution of anodes in gravel and activated charcoal filters is different. Cathodic protection of activated charcoal filters is basically feasible but requires a large number of electrodes and high protection current densities that are twice those for gravel bed filters, so that an electrically insulating layer can be deposited on the steel wall. 

Figure 21-1 shows the object to be protected and the arrangement of impressed current anodes and reference electrodes. A central anode and two ring anodes of platinized titanium wire 3 mm in diameter provided with additional copper wire conductors are installed here. It is worth noting that the central anode is suspended from a float, whereas the ring anode is mounted on plastic supports. The zinc reference electrodes are also on floats near the inner side of the bell, while the 17 reference electrodes are mounted on plastic rods on the bottom of the cup and in the ring... 

An electrochemical cell in which electrolysis takes place is called an electrolytic cell. The arrangement of components in electrolytic cells is different from that in galvanic cells. Typically, the two electrodes share the same compartment, there is only one electrolyte, and concentrations and pressures are far front standard. As in all electrochemical cells, the current is carried through the electrolyte by the ions present. For example, when copper metal is refined electrolytically, the anode is impure copper, the cathode is pure copper, and the electrolyte is an aqueous solution of CuS04. As the Cu2f ions in solution are reduced and deposited as Cu atoms at the cathode, more Cu2+ ions migrate toward the cathode to take their place, and in turn their concentration is restored by Cu2+ produced by oxidation of copper metal at the anode. 

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