Cathodic protection continued design

In plain tinplate cans for acid foods, tin provides cathodic protection to steel (3,4). The slow dissolution of tin prevents steel corrosion. Many investigators (5-1I) have defined this mechanism in detail and have shown that the tin dissolution rate is a function of the cathodic activity of the base steel, the steel area exposed through the tin and the tin-iron alloy layers, and the stannous ion concentration. Kamm et al. showed that control of the growth of the tin—iron alloy layer provides a nearly continuous tin-iron alloy layer and improves the corrosion resistance of heavily coated (over 45 X 10"6 in. tin) ETP for mildly acid food products in which tin provides cathodic protection to steel (12). The controlled tin-iron alloy layer reduces the area of steel exposed to the product. ETP with the controlled alloy is designated type K, and since 1964, 75 type K ETP has been used to provide the same protection as 100 ETP provided previously (13). 

Hoffman and co-workers have carried out a series of studies on the passive films on iron, with particular attention to cell design. They have employed a so-called bag cell that allows for the in-situ passivation or cathodic protection of the iron films which were deposited onto gold films deposited on melinex (polymer film with excellent adhesive properties). In addition, they employed a setup in which the working electrode is partially immersed in solution and continuously rotated. In this way, they could expose the electrode to the x-ray beam with ostensibly only a very thin film of electrolyte. Under these conditions, they were able to obtain spectra of the film as prepared, a cathodically protected film as well as a film passivated in borate solution at 1.3 V. From an analysis of their data, they concluded that the passive film had an Fe—O coordination with 6 near neighbors at a distance of 2 + 0.1 A. The approach followed by these authors appears most appropriate since they were able to reduce the deposited films... 

Thermogalvanic corrosion is prevented by appropriate design and measures to avoid uneven heating/cooling and forming of hot spots. For heat-insulated pipes and equipment is important that the insulation is continuous. The corrosion form may under certain conditions be prevented by cathodic protection or coatings. 

Low resistivities and high chloride concentrations in the soil may lead to corrosion of buried steel pipehnes or structures. Cathodic protection should be considered for all buried steel pipehnes or structures. Where cathodic protection is not provided, corrosion monitoring equipment should be incorporated into the design to allow the operating staff to monitor the condition of the pipelines or structures. Nonwelded joints should be bonded for electrical continuity. In addition, coatings should also be considered. Coatings may be used alone or in con-jimction with cathodic protection. 

Electrochemical protection is divided into cathodic and anodic protection. Cathodic protection based on the change of potential of a metal in the negative direction is realized in electrolytic environments, in most cases neutral, mainly of steel and reinforced concrete structures. A well-designed and correctly realized CP reduces the corrosion rate to almost zero. In practice it is realized with the use of an impressed current or protectors (galvanic anodes). The scope of application is enormous and continuously increases. With the use of this technology it is possible to protect vessels and ships, docks, berths, pipelines, deep wells, tanks, chemical apparatus, underground and underwater municipal and industrial infrastructure, reinforced concrete... 

For these reasons, the cathodic corrosion protection of chemical plant parts is restricted to neutral solutions, service water, and alkalis. Various types of anodes are available for the protection of container interiors. Platinized disk electrodes, bar anodes, and titanium basket anodes are used. They are now supplied ready for installation and are designed in such a way that, in continuous operation, they can emit 8-10 A at a current density of 6-8 A/dm. ... 

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