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5 Corrosion Protection for Buried Steel
Pages 49-56

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From page 49...
... In contrast, oil and gas pipeline industries generally favor a "corrosion protection" approach, which employs protective physical barriers as well as CP to avoid corrosion. Water utilities generally focus little on external corrosion of water pipelines, tolerating leaks and addressing breakages as they happen.
From page 50...
... Box 5.1 provides a brief description of these different coatings and when they were introduced. Like oil and gas pipelines, water pipeline coatings can include hot-applied coal tar enamel, FBE, or PE, but also commonly include liquid epoxy systems, extruded PE, wax tape, sacrificial metallic coatings, and cement coatings.
From page 51...
... Other coatings such as polyvinyl chloride and polyurea are also used for coating buried steel pipes. 1940s–1950s: Coal tar (bituminous enamel)
From page 52...
... Once the zinc or magnesium anodes are consumed, they need to be replaced for corrosion protection to continue. The service life of the anodes is considered in the design phase of steel structures, but future maintenance and replacement of anodes must continue throughout the life cycle of the steel structures.
From page 53...
... In the pH ranges below 4 and beyond 8.5, the passive film will dissolve and no longer provide protection, and the corrosion rate of aluminized steel will be higher than that of galvanized steel. Impressed Current Cathodic Protection In some applications, the potential difference between sacrificial anode(s)
From page 54...
... Finally, ICCP has a greater likelihood of creating stray-current interferences on other steel infrastructure in the vicinity. Cathodic polarization of a buried steel surface immediately reduces the kinetically controlled iron dissolution rate and increases the cathodic reduction rate on the steel surface.
From page 55...
... Furthermore, increased pH that typically accompanies cathodic polarization can be significantly reduced by the presence of biofilms that provide a chemical pH buffering capacity. Overall, there is general agreement that more negative protection potentials are needed for CP in the presence of iron sulfides, but there are unwanted consequences of extreme cathodic polarization.
From page 56...
... to remove Finer fractions (i.e., those passing the #40 sieve) may be more fractions containing soluble salts corrosive due to lower pH and resistivity and higher sulfate concentration.


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