Soils corrosion protection

Cathodic Protection This electrochemical method of corrosion control has found wide application in the protection of carbon steel underground structures such as pipe lines and tanks from external soil corrosion. It is also widely used in water systems to protect ship hulls, offshore structures, and water-storage tanks. 

Corrosion susceptibility in aqueous media is assessed on the basis of the rating numbers [3, 14], which are different from those of soils. An increased likelihood of corrosion is in general found only in the splash zone. Particularly severe local corrosion can occur in tidal regions, due to the intensive cathodic action of rust components [23, 24]. Since cathodic protection cannot be effective in such areas, the only possibility for corrosion protection measures in the splash zone is increased thickness of protective coatings (see Chapter 16). In contrast to their behavior in soils, horizontal cells have practically no significance. 

For corrosion protection in soils, the anodes can be brought close to the object to be protected in the same construction pit so that practically no further excavations are needed. By connecting anodes to locally endangered objects (e.g., in the case of interference by foreign cathodic voltage cones) the interference can be overcome (see Section 9.2.3). 

With buried pipelines, the degree of corrosion danger from cell formation and the effectiveness of cathodic protection can be determined by pipe/soil potential measurements along the pipeline (see Sections 3.6.2 and 3.7). This is not possible with well casings since the only point available for a measuring point is at the well head. Therefore, other methods are required to identify any corrosion risk or the effectiveness of corrosion protection. 

In this chapter some important equations for corrosion protection are derived which are relevant to the stationary electric fields present in electrolytically conducting media such as soil or aqueous solutions. Detailed mathematical derivations can be found in the technical literature on problems of grounding [1-5]. The equations are also applicable to low frequencies in limited areas, provided no noticeable current displacement is caused by the electromagnetic field. 

An alternative means of avoiding the hazard from fire is to bury the vessels or to employ the increasingly popular method of mounding. In either case, acknowledgment of the reduced hazard is indicated by the reduced separation distances (see Table 20.4). Since both burial and mounding preclude the possibility to monitor continuously the external condition of the vessels, very high-quality corrosion protection needs to be applied, often supplemented by cathodic protection, depending on soil conditions. 

Silicates. Both sodium and potassium silicate solids or solutions have valued functionality including emulsification, buffering, deflocculation, and antiredeposition ability. Silicates also provide corrosion protection to metal parts in washing machines, as well as to the surfaces of china patterns and metal utensils in automatic dishwashers. Silicates are manufactured in liquid, crystalline, or powdered forms and with different degrees of alkalinity. The alkalinity of the silicate provides buffering capacity in the presence of acidic soils and enhances the sequestration ability of the builder system in the formulation. The sili-cate/alkali ratios of the silicates are selected by the formulator to meet specific product requirements. Silicate ratios of 1/1 are commonly used in dry blending applications with silicate ratios of 2/1 and higher commonly used in laundry and autodish applications. 

Hydroxyethyl)-2-hept ec-enyl-2-imidazoline 1-Hydroxyethyl-2-heptadecenyl-glyoxalld-lne 1H-lmidazole-1-ethanol, 2-(8-heptadec-enyl)-4,5-di-hydro- 2-lmidazoline-1-ethanol, 2-(8-hepta-decenyl)- Marlowe 5440 Nalcamine G-13 NSC 231649 Oleyl imidazoline Sovatex IM17H UCL 5410. Used as an emulsifier for mineral oils, corrosion protection, car wash rinses. Also used as a fungicide and soil stabilizer, corrosion Inhibitor lubricant antistatic agent as a base for cationic surface active agents. See USP 2,987,515 3,020,276. Baker Petrolite Corp. Hills Am. 

The second system is based on the application of impressed current that is forced through anodes to the protected structure such as the tank by a current source of sufficient potential. Properly designed CP systems that are well maintained and operate at the correct current density are a proven method of protecting tanks from the corrosive effects of contact with corrosive soils. In addition to protection of underground tanks, CP is also useful for aboveground double-bottom tanks and for internal corrosion protection. 

Figures 5.72 and 5.73 show the corrosive attack on samples of cast iron pipe and ductile iron pipe buried under the soil for 20 and 9 years, respectively. The large hole in cast iron pipe (Fig. 5.72) and the corrosion pit and perforation in ductile iron pipe (Fig. 5.73) show the severity of soil corrosion. It is suggested that cathodic protection can reduce the extent of corrosion of iron pipes.

Despite some possible implementation problems and the need for sophisticated requirenwnts for interpretation, these measurements can prove particularly valuable in low conductivity media -such as concrete, soils, condensate corrosion, protection by coatings etc. They therefore provide a more accurate determination of R. ... 

RJ- Kuhn, Cathodic protection of underground pipe lines from soil corrosion, API Proc. 14 (1933) 157-167. 

H.C. Van Nouhuys, Cathodic protection and high soil resistivity soil. Corrosion 9 (1953) 448-459. 

F. Kajiyama, K. Okamura. Evaluating cathodic protection reliability on steel pipes in microbially active soils. Corrosion, Vol. 55, No. 1, pp. 74—80, 1999. 

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