The problem with passive protection is that no coating is perfect or permanent. During manufacturing, transport, installation, or simply over time, localized defects known as holidays appear: small discontinuities in the coating where the metal is exposed to the electrolyte. A single holiday is enough for corrosion to start at that specific point, in a localized and often more aggressive way than if there were no coating at all. <\/p>\n\n
![\"Defect](\"https:\/\/procainsa.com\/wp-content\/uploads\/defecto-holiday-revestimiento-tuberia-1024x683.webp\")
<\/figure>\n\nWhat is active protection or electrochemical cathodic protection<\/h2>\n\n
Active protection, which we normally refer to simply as cathodic protection, does not attempt to isolate the metal from the electrolyte, but rather to change its electrochemical behavior. The metal structure becomes the cathode of an electrochemical cell, so that instead of losing electrons (oxidizing, corroding) it receives them from an external source. <\/p>\n\n
Esa fuente externa puede ser un metal m\u00e1s reactivo que se sacrifica en su lugar (\u00e1nodos de sacrificio) o una corriente el\u00e9ctrica controlada suministrada por un rectificador (protecci\u00f3n cat\u00f3dica por corriente impresa). A diferencia de la protecci\u00f3n pasiva, la protecci\u00f3n activa sigue funcionando incluso en los puntos donde el revestimiento ha fallado, precisamente porque no depende de una barrera f\u00edsica. <\/p>\n\n
Why passive protection alone is not enough<\/h2>\n\n
No serious corrosion engineer recommends relying solely on coating for critical installations. The reasons are clear: <\/p>\n\n
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- Todo revestimiento, por bueno que sea, desarrolla defectos con el tiempo.<\/li>\n\n\n\n
- Los defectos no son visibles desde el exterior en una tuber\u00eda enterrada o sumergida.<\/li>\n\n\n\n
- Corrosion at a holiday point can be faster and more localized than generalized corrosion.<\/li>\n\n\n\n
- Repairing a damaged coating in a buried installation involves excavation, with the cost and operational disruption that entails.<\/li>\n<\/ul>\n\n
That is why reference international standards, such as NACE SP0169 and ISO 15589, require active cathodic protection for critical buried and submerged pipelines, regardless of the quality of the applied coating.<\/p>\n\n
Comparison table between passive protection and active cathodic protection<\/h2>\n\n
Aspect<\/th> Protecci\u00f3n pasiva (revestimientos)<\/th> Active protection (cathodic)<\/th><\/tr><\/thead> Operating principle<\/td> Isolates the metal from the electrolyte using a physical barrier<\/td> Converts the metal into the cathode of an electrochemical cell<\/td><\/tr> Protects against corrosion on its own<\/td> Only while the coating remains intact<\/td> Yes, continuously throughout its design service life<\/td><\/tr> Requires electric current<\/td> No<\/td> Only in the case of impressed current; not in sacrificial anodes<\/td><\/tr> Vulnerable to localized defects<\/td> Yes, a single holiday can initiate localized corrosion<\/td> No, it also protects at points where the coating fails<\/td><\/tr> Requires periodic maintenance<\/td> Visual inspection and spot repair<\/td> Potential verification and anode replacement or rectifier adjustment<\/td><\/tr> Relative initial cost<\/td> Bajo a medio<\/td> Medio a alto, seg\u00fan extensi\u00f3n de la instalaci\u00f3n<\/td><\/tr> Recommended use<\/td> As a first line of defense in any buried or submerged metallic installation<\/td> As a mandatory complement in critical installations, covering coating failures<\/td><\/tr><\/tbody><\/table><\/figure>\n\n How passive protection and active cathodic protection are combined in practice<\/h2>\n\n
En el dise\u00f1o de ingenier\u00eda moderno, la protecci\u00f3n pasiva y la protecci\u00f3n cat\u00f3dica activa no se plantean como alternativas, sino como dos capas de un mismo sistema de protecci\u00f3n frente a la corrosi\u00f3n:<\/p>\n\n
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- El revestimiento<\/strong> act\u00faa como primera l\u00ednea de defensa, reduciendo dr\u00e1sticamente la superficie met\u00e1lica expuesta al electrolito.<\/li>\n\n\n\n
- La protecci\u00f3n cat\u00f3dica activa<\/strong> act\u00faa como segunda l\u00ednea, protegiendo espec\u00edficamente los puntos donde el revestimiento ha fallado.<\/li>\n<\/ul>\n\n
This combination has a very relevant additional advantage from an economic point of view: by reducing the exposed metallic surface, the cathodic protection current needed to protect the entire installation is reduced by several orders of magnitude compared to what would be required to protect the same structure without any coating. This allows for the design of smaller, more economical cathodic protection systems with longer-lasting anodes. <\/p>\n\n
Cu\u00e1ndo es imprescindible a\u00f1adir protecci\u00f3n cat\u00f3dica activa al revestimiento<\/h2>\n\n
Although it is advisable to combine both whenever possible, there are scenarios where active cathodic protection ceases to be a recommendation and becomes a requirement:<\/p>\n\n
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- Buried or submerged pipelines for gas, oil, or chemical products, where a leak has serious safety or environmental consequences.<\/li>\n\n\n\n
- Installations subject to regulations that explicitly require cathodic protection, such as regulated gas pipelines, oil pipelines, or storage tanks.<\/li>\n\n\n\n
- Instalaciones con una vida \u00fatil de dise\u00f1o larga (d\u00e9cadas), donde la degradaci\u00f3n acumulada del revestimiento a lo largo del tiempo es inevitable.<\/li>\n\n\n\n
- Buried or submerged installations with difficult access, where inspecting or repairing the coating is costly or unfeasible.<\/li>\n<\/ul>\n\n
Necesita evaluar si su instalaci\u00f3n cuenta con la protecci\u00f3n adecuada?<\/strong>
- La protecci\u00f3n cat\u00f3dica activa<\/strong> act\u00faa como segunda l\u00ednea, protegiendo espec\u00edficamente los puntos donde el revestimiento ha fallado.<\/li>\n<\/ul>\n\n
- El revestimiento<\/strong> act\u00faa como primera l\u00ednea de defensa, reduciendo dr\u00e1sticamente la superficie met\u00e1lica expuesta al electrolito.<\/li>\n\n\n\n