Cathodic protection design

Table 10.13 Current density used in ship hull cathodic protection design...

The latter part of this chapter has dealt with the design considerations for a sacrificial anode cathodic protection system. It has outlined the important parameters and how each contributes to the overall design. This is only an introduction and guide to the basic principles cathodic protection design using sacrificial anodes and should be viewed as such. In practice the design of these systems can be complex and can require experienced personnel. 

Det norske Veritas Recommended Practice, Cathodic Protection Design, RP B401, March (1986). This document has been superseded by RP B401 (1993)... 

Evans, T. E., Mechanisms of Cathodic Protection in Seawater . In Cathodic Protection Theory and Practice, 2nd International Conference, Stratford-upon-Avon, June (1989) Choate, D. L., Kochanezyk, R. W. and Lunden, K. C., Developments in Cathodic Protection Design and Maintenance for Marine Struaures and Pipelines , NACE Conference on Engineering Solutions for Corrosion in Oil and Gas Applications, Milan, Italy, November (1989) not included in Proceedings... 

Howell, P. P., Potential Measurements in Cathodic Protection Design , Corrosion, 8, 300 (1952)... 

With steady development in the modeling methods and computational techniques, this approach is expected to rule the future of cathodic protection design. Development of models has lead to a widespread increase in the theoretical understanding of the system. In the future it is expected to play wide role in developing new designs without wasting money on field experimental projects. 

L. E. Carlson, J.H. Prrzgerald III, F.R.D. Webster, Cathodic protection design for 1,900 miles (3,050 km) of high-pressure natural gas pipeline. Mater. Performance 40 (2001) 28—32. 

R.M. Degerstedt, K.J. KenneUey, M.E. Orazem,J.M. Estehan, Computer modeling aids. Traditional cathodic protection. Design methods for coated pipelines, Mater. Performance 35 (1996) 16—20. 

Det norske Veritas Industri Norge AS. Recommended practice, RP B401, Cathodic protecting design, 1993. 

In cathodic protection design, it is essential to be able to estimate the anode output and its lifetime. From these estimates, anode spacing over the structure to be protected can be calculated (i.e., the number of anodes required to protect the structure). 

Morgan, J. H., Instruments for Cathodic Protection . Corros. Techno ., 4, 269 (1957) Howell, P. P., Potential Measurements in Cathodic Protection Design , Corrosion, 8, 300 (1952)... 

The problem of corrosion of steel in concrete was first ascribed to stray current flows from trams and DC railway systems Hime, 1994). Once chloride, in the form of deicing salt, was identified as the major culprit (when trams disappeared but corrosion increased), an enterprising engineer in the California Department of Transportation (Caltrans) took a standard pipeline cathodic protection design and flattened it out on a bridge deck. 

Sacrificial Anode Tedmique (SAT) It can also be used to protect an uncoated (bare) stmctures, seagoing vessels, offshore tanks, offshore platforms, water heater, and the like. In fact, a cathodic protection design using sacrificial anodes requires several anodes. These anodes must be monitored frequently because they dissolve sacrificiaUy (purposely) and eventually are reduced in size and become incapable of delivering the necessary current to the stmcture. 

In addition, anodes are classified as sacrificial anodes and impressed-current anodes. The former must be anodic to the stmcture and must dissolve at a low rate, providing electrons to the cathode. On the other hand, the latter must have low consumption rates in cathodic protection designs. Specifically, sacrificial magnesium Mg) anodes are widely used in buried pipelines and domestic or industrial water heater applications. For instance, a Mg anode may protect as much as 8 Km of a coated pipeline buried in the seal [3]. 

The following formulae are compiled from Currer and Gerrard [13] and Hei-dersbach [9], Other formulas for specific cathodic protection design can be found elsewhere [14-16]. The electrolyte-to-anode resistance equations are given in Table 8.5. 

Figure 5.39 Determination of coating resistance. (From TEXACO Cathodic Protection - Design and application school, Texaco Houston Research Center, Training Manual. Reproduced by kind permission of Cheveron, Houston Research Center, USA)...

West, L.H. and Lewicki, T.F. (1974). Cathodic protection design. Civil Engineering Corrosion Control, Vol. 35,61-73, AFCEC Technical Repot No. 74-76, Tyndall, Florida AFB, USA. 

In many instances, the cathodic protection design entailed the use of shallow "deep wells," approximately 50 feet deep, sunk in coral caves full of seawater. 

A common cathodic protection design is the use of bracelet anodes that originally were zinc but now, with improved alloys, are usually aluminum. Alternately, high-silicon cast iron anodes mounted on sleds, buried in the sea bed 250 feet from a given pipeline and midway between shore and the spar buoy ship connection have performed well. Anode return cables can be a maintenance problem unless properly secured to the pipelines and buried at least 5 feet into the sea bed, between the pipelines and the anode sled. Anode beds can also be installed in the beach itself, but they must be deep enough to be in the saltwater intrusion area. 

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