Application of Magnesium Anode for Cathodic Protection of Buried Thermally Insulated Metallic Pipeline

Abstract The external anti-corrosion and thermal insulation structure of buried thermally insulated metallic pipeline typically consists of an electrically insulated outer jacket, thermal insulation layer, and anti-corrosion coating. Due to the cathodic protection (CP) shielding effect of the outer jacket and the confined space within the thermal insulation layer, CP current from traditional remote groundbeds struggles to reach coating defects on thermally insulated pipelines. Consequently, effective protection of the pipeline substrate is compromised. As a result, corrosion under insulation (CUI) becomes the primary factor in external corrosion failure of buried thermally insulated metallic pipelines. In this work, application of magnesium alloy sacrificial anode for cathodic protection of buried thermally insulated metallic pipeline is investigated by field experiments, potentiodynamic polarization measurements, and numerical simulation. The results show that magnesium ribbon anodes installed inside the thermal insulation layer can provide enough cathodic protection to thermally insulated metallic pipeline when thermal insulation layer flooding occurs due to jacket damage. The protection length correlates with performance of the anti-corrosion coating. For 3PE-coated pipelines, a 1-meter magnesium ribbon anode can provide 4-5 m of effective unidirectional protection length. Considering standard pipe lengths of 12 m, installing built-in magnesium ribbon anodes within the thermal insulation layer at low-lying sections (prone to water accumulation) presents an effective solution for mitigating CUI risks of buried thermally insulated metallic pipelines.