Mortar Coated and Lined Concrete Cylinder Pipe
Concrete pipelines, when installed correctly, have inherently high pH values. The high alkalinity environment provided by the concrete or mortar coatings allows the steel surface of the pipe to passivate, mitigating the potential to be affected by the environment and electrochemically corroded. When there is a breakdown in the protective qualities of the mortar coating, the alkalinity reduces (lowering the pH), steel passivation is lost, and corrosion is initiated.
Without the application of an externally impressed voltage, steel embedded concrete, that is successfully being passivated, has a potential voltage of 0 to -200 mV in reference to a copper-copper/sulfate reference electrode. A more negative shift in the potential of steel in concrete could indicate damage in the mortar coating, stray current, or possible corrosion activity.
In 2017, ICG performed a close interval survey to determine sites to excavate and evaluate the coating on a 96" Mortar Coated and Lined Concrete Cylinder Pipe (MLCP). A temporary ground bed was set up and 710mA of current was applied to the pipeline. The pipe-to-soil potential data collected during the survey was then used to identify areas where potential coating damage could be located. These areas are identified in the plot below, indicated by the large peaks. The recommended sites were then excavated and it was found that the coating at these locations was in fact deteriorating, and corrosion activity on the pipe surface beneath had also initiated.