Corrosion prevention cathodic

Corrosion. Anticorrosion measures have become standard ia pipeline desiga, coastmctioa, and maintenance ia the oil and gas iadustries the principal measures are appHcation of corrosion-preventive coatings and cathodic protection for exterior protection and chemical additives for iaterior protectioa. Pipe for pipelines may be bought with a variety of coatiags, such as tar, fiber glass, felt and heavy paper, epoxy, polyethylene, etc, either pre-apphed or coated and wrapped on the job with special machines as the pipe is lowered iato the treach. An electric detector is used to determine if a coatiag gap (hoHday) exists bare spots are coated before the pipe is laid (see Corrosion and corrosion control). 

Corrosion prevention (liners, coatings, cathodic protection)... 

Spencer, K. A, in Anti-Corrosion Manual, Scientific Surveys Ltd., London, 359 (1962) Vrable, J. B., Protecting Underground Steel Tanks , Mat. Prot., 6 No. 8, 31, August (1967) West, L. H., Cathodic Protection —The Answer to Corrosion Prevention of Underground Structures , Mat. Prot., 7 No. 7, 33, July (1968)... 

The selection of an alloy for a specific application is based on the cost and the corrosion resistance of the alloy in the environment of interest. It is also possible to subject the chosen alloy to a process by which the corrosion resistance of the selected material can be improved within the acceptable limits. Some of the corrosion prevention and protection strategies with respect to the aluminum-based alloys are (i) design (ii) alloy selection and joint sealants (iii) aluminum thermal spraying anodic coatings (iv) inhibitors (v) conversion and organic coatings and (vi) cathodic protection. 

Corrosion prevention—material selection, corrosion inhibition, cathodic protection, galvanic corrosion prevention, and extensive nondestructive and destructive inspection protocols. ... 

Corrosion protection (cathodic) to prevent water ingress Active... 

On the other hand, anything that makes iron behave more like the cathode prevents corrosion. In cathodic protection, iron makes contact with a more active metal (stronger reducing agent), such as zinc. The iron becomes cathodic and remains intact, while the zinc acts as the anode and loses electrons (Figure 21.2IB). Coating steel with a sacrificial layer of zinc is the basis of the... 

Inhibitors are used in severe and harsh environments encountered in rotary cookers and hydrostatic sterilizers. The medium consists of hot water, steam, and cooling water. A single approach to this problem may not provide the solution. A combination of anodic, cathodic, and filming inhibitors was selected for corrosion prevention depending on the water composition and equipment material. 

Uhlig s study (7) attempted to measure the costs of corroding structures to both the owner/operator (direct cost) and to others (indirect costs). The total cost of corrosion to owner/operators was estimated by summing the cost estimates for corrosion prevention products and services used in the entire US economy such as coatings, inhibitors, corrosion-resistant metals, and cathodic protection and multiplied these totals by their respective prices. Domestic water heater replacement, automobile internal combustion engine repairs, and replacement of automobile mufflers were selected as examples to estimate the cost to private consumers/users. Adding both the direct and indirect costs, the annual cost of corrosion to the United States was estimated to be 5.5 billion or 2.1% of the 1949 GNR This method was used in Japan and estimated the cost of corrosion at 9.2 billion equivalent to 1-2% of the Japanese GNR. 

A final approach to corrosion prevention is the use of an inhibitor, defined as a substance used in small concentrations that decreases the rate of corrosion. Most inhibitors are organic compounds that form adsorbed layers on the metal surface. This provides a system similar to the protective coatings discussed earlier. Other inhibitors affect gaseous reduction reactions associated with the cathode (Table 20.5). 

The anodic and cathodic reactions ((2.1) and (2.2)) are only the first steps in the process of creating rust. However, this pair of reactions is critical to the understanding of corrosion and is widely quoted in any discussion on corrosion and corrosion prevention for steel in concrete. The reactions will be referred to often in this book. 

Figure 13.23 I Sacrificial anodes are one effective method of corrosion prevention. An unprotected iron or steel pipe buried in the ground would be at high risk for corrosion. By connecting the buried pipe to a metal such as magnesium, which is more easily oxidized, a galvanic cell is created with the pipe as the cathode. In the case of a buried pipe, the soil itself serves as the electrolyte. The anode is called sacrificial because it will be eaten away over time by oxidation. But replacing the anode—which may be nothing more than a metal block or stake—is much easier than replacing the buried pipe.

Corrosion prevention is another area where accurate published data were unavailable. In 1958 and 1963, the share of this component in the total electrochemical industry was approximately 3 %. Our estimate of the value of shipments of corrosion prevention products, which function electrochemically, was 147.7 MM in 1958 and 192.9 MM in 1963. The corrosion prevention products which were considered in this study were zinc coatings and cathodic protection systems. The estimates of the 1958 and 1963 shipments of zinc coatings were made by a representative of a leading firm in the zinc coating market. This estimate for 1958 was 3.0 MM and for 1963 8.0 MM. These figures only include the cost of the materials applied. The cost of application, which may equal many times the cost of materials, is excluded. The value added by zinc coatings was obtained from the value added-shipments ratio of the appropriate SIC category in the Census of Manufactures. 

Tighe-Ford, D. J., McGrath, J. N., and Hodgkiss, L., "Design Improvements for a Ship s Cathodic Protection System Using Dimension and Conductivity Scaling (DACS), Corrosion Prevention and Control, Vol. 32, No. 5, October 1985, pp. 89-91. 

Seven primary corrosion prevention methods are available to reduce the corrosion of metals material selection, electrical isolation, electrical bonding, environmental modification, inhibitors, coatings, and cathodic protection. Corrosion prevention methods are often used in conjunction with one another. Coatings are used to reduce current requirements in cathodic protection. Zinc is used as a cathodic protection system in coatings. The effects of two or more corrosion prevention systems can be synergistic or antisyner-gistic. Two effects are synergistic if the combination of the two is more effective than the sum effect of the two. 

Recognize corrosion problems in materials used at the site and make monitoring a normal part of the operation. Sour oil and gas operations are often conducted under high pressure and corrosive conditions. Therefore, in addition to temperature and pressure considerations, system designs for the wellhead, downhole equipment, and pipeUnes must have features to minimize the effects of corrosion and prevent an accidental release of H2S. Corrosion-inhibiting fluids can be used to prevent internal corrosion and cathodic protection can be used to prevent external corrosion. Also, during extended periods of shut-in and injection into pipelines, inhibitor applications may be beneficial. 

The principles for corrosion and cathodic protection is illustrated in Figure 82 for an iron or carbon steel structure. Conx)sion occurs at a slow or fast rate of iron dissolution in the aerated electrolyte since it is the iron atoms that release electrons, which are needed for the reduction of water to form hydroxyl ions in the electrolyte, such as air or son. On the other hand, cathodic protection is achieved by supplying external electrons to the stmcture. Thus, the amount of external electrons reduce significantly or prevent the rate of dissolution of iron, but hydroxyl ions stiU form on the stmcture surface. 

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