Pipelines cathodic protection, costs

The low cost, light weight, and exceUent electrical conductivity of graphite anodes have made this impressed current protection system valuable for cathodic protection of pipelines, storage vessels, process equipment, and also for weU casings both on- and offshore. 

Cathodic protection of uncoated objects in the soil is technically possible however, the high current requirement, as well as measures for the necessary uniform current distribution and for //f-free potential measurement, result in high costs. In determining the costs of cathodic protection of pipelines, it has to be remembered that costs will increase with increases in the following factors ... 

The following economic considerations apply particularly to the cathodic protection of pipelines. The total cost of protection with galvanic anodes should be less than the costs of an impressed current installation K q. 

In order to carry out a cost comparison of cathodic protection with the prolongation of service life of pipelines that it provides, the construction costs and the material costs of the pipeline have to be known. If there are no particular difficulties (e.g., having to lay the pipe in heavily built-up areas, river crossings, or rocky soil), the construction costs for a high-pressure DN 600 pipeline are about 10 DM km". If it is simply assumed that a pipeline has a useful life of 25 years without cathodic protection whereas with cathodic protection it has a life of at least 50 years, the... 

These considerations are always relevant to water pipelines, which must have a very long service life. With natural gas, oil, and product pipelines, shorter periods are usually assumed for depreciation. Disregarding the fact that in this case cathodic protection is compulsory for safety reasons and protection of the environment, the costs of repairs resulting from wall perforation after a long service life can exceed the costs of cathodic protection. 

Further chapters cover in detail the characteristics and applications of galvanic anodes and of cathodic protection rectifiers, including specialized instruments for stray current protection and impressed current anodes. The fields of application discussed are buried pipelines storage tanks tank farms telephone, power and gas-pressurized cables ships harbor installations and the internal protection of water tanks and industrial plants. A separate chapter deals with the problems of high-tension effects on pipelines and cables. A study of costs and economic factors concludes the discussion. The appendix contains those tables and mathematical derivations which appeared appropriate for practical purposes and for rounding off the subject. 

These anodes, like platinised Ti may be supplied in different forms e.g. rod, tube, mesh, wire, etc. They may be used for the cathodic protection of offshore structures, heat exchangers, or even pipelines as they can be installed in the soil surrounded by carbonaceous backfill, and are comparable in cost to platinised titanium. ... 

Coatings, cathodic protection, and chemical additives are used extensively to prevent internal and external pipeline corrosion. The excessive use of incompatible chemical additives has caused severe problems in gas-transporting systems. Costs arising from these problems often exceed the costs of the chemicals themselves. The careful evaluation and selection of chemical additives can minimize these problems and reduce operating costs [I860]. 

The cost of building a pipeline is usually divided into four categories materials (line pipe, fittings coatings, cathodic protection, etc), right-of-way... 

Cathodic protection has many problems and limitations apart from huge capital investment and maintenance costs. One of the more serious problems associated with cathodic protection is the possible effects of stray currents on the corrosion of adjacent metal structures. For example, a CP system that is efficiently protecting pipeline A might increase the corrosion of neighboring pipeline B (Fig. 10a). 

Corrosion is both costly and dangerous. Billions of dollars are spent annually for the replacement of corroded structures, machinery, and components, including metal roofing, condenser tubes, pipelines, and many other items. In addition to replacement costs are those associated with maintenance to prevent corrosion, inspections, and the upkeep of cathodically protected structures and pipelines. Indirect costs of corrosion result from shutdown, loss of efficiency, and product contamination or loss. 

Economic losses are divided into (1) direct losses and (2) indirect losses. Direct losses include the costs of replacing corroded structures and machinery or their components, such as condenser tubes, mufflers, pipelines, and metal roofing, including necessary labor. Other examples are (a) repainting structures where prevention of rusting is the prime objective and (b) the capital costs plus maintenance of cathodic protection systems for underground pipelines. Sizable direct losses are illustrated by the necessity to replace several million domestic hot-water tanks each year because of failure by corrosion and the need for replacement of millions of corroded automobile mufflers. Direct losses include the extra cost of using corrosion-resistant metals and alloys instead of carbon... 

For buried pipelines, the cost of cathodic protection is far less than for any other means offering equal assurance of protection. The guarantee that no leaks will develop on the soil side of a cathodically protected buried pipeline makes it economically feasible, for example, to transport oil and high-pressure natural gas across entire continents. 

In recent years, continuous zinc ribbon anodes have been used in a variety of underground applications (Kurr, 1973 Peabody, 1976 O Connell, 1977). This type of product has broadened the applications for zinc anodes, for it provides small increments of current continuously along the entire length of a cathode. Its uses are generally considered to lie in specialty applications, where other methods of cathodic protection are either impractical or extremely costly (see later section on induced ac on pipelines). Bagnulo (1973, 1984) has developed a tape with an electrically conducting adhesive as described in the Mechanical Coatings part of Chapter 1. 

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