Buried and submerged pipelines need external coating + cathodic protection to operate safely over the years.
ANALYSIS
External Coating + Cathodic Protection: the Safe Way to Protect Buried and Submerged Pipelines Luiz Paulo Gomes IEC-Instalações e Engenharia de Corrosão Ltda. – Rio de Janeiro, Brazil LPgomes@iecengenharia.com.br
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uried or submerged steel pipelines are of fundamental importance to the modern world in the transportation of oil, gas, oil products,
phenomenon, completely eliminating corrosion cells. If the coating fails due to the insulation barrier deȴciency, which is always
ores, water, chemicals and other ȵuids. To ensure the integrity and long
the case in practice, the cathodic protection system complements this
life of these pipes, it is necessary to protect them against corrosion by
failure and ensures full protection of the pipeline by modifying the
using anti-corrosion protective coatings, always complemented by a
potential of the buried or submerged pipes.
cathodic protection system. The cathodic protection system functions
For example, we know that potential pipe to soil or potential pipe to
as if a perfect liner had been used in buried or submerged piping as the
water equal to or more negative than minus 0.85V, measured with the
cathodic protection current looks for coating failures and protects these
Cu/CuSO4 reference electrode, provides protection against corrosion of
locations from corrosion (Fig. 1).
buried or submerged pipes, regardless of condition of the coating.
In this way the coating failures are compensated by the cathodic protection
In order to select the most suitable type of coating and the most eɝcient
system, which injects electric current and modiȴes the potentials of the pipe
cathodic protection method (galvanic or impressed current), we need
in relation to the ground or water. As can be seen, while the anti-corrosion
to consider some important factors such as the transported product,
coating acts as an insulating barrier, cathodic protection is an electrical
the aggressiveness of the soil or water and the existence of sources
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N.32 - 2019 DECEMBER - ipcm® Protective Coatings