Does CP System Monitoring Data Confirm that your Structure is not Corroding?
Unfortunately, the answer is no… While test data from a functioning cathodic protection (CP) system may indicate that there is full corrosion protection of a structure, it is important to verify this data by conducting an on site audit to confirm the corrosion status of the structure’s elements.
For structures with steel piles in water, some of the common causes of inadequate protection include:
Poor continuity of some of the steel piles.
Failure to adjust the cathodic protection current to achieve the necessary level of polarisation, for example in cases where there is the presence of Microbiologically Influenced Corrosion (MIC) .
Inadequacies in the testing methodology for the CP system including system adjustment based on data from reference electrodes which may have not been properly calibrated.
For concrete structures, some of the common causes of inadequate localised protection include:
Poor continuity of the embedded steel reinforcement (which may not have been detected during the design and construction stage of the CP system).
Partial failure of some components of a CP system. For instance, failure of terminals or cables in the junction boxes which cannot be detected from the T/R unit due to design shortcomings.
Over-reliance on system assessment ie. adjustment based on data from the embedded reference electrodes which may have not been installed in representative locations during construction.
A prudent starting point would be to carry out a detailed audit of the structure and CP system. The aim of such an audit would be to verify whether the elements of the structure are cathodically protected, identify any corrosion problems by visual inspection and targeted testing, and provide recommendations for any required rectification work.
The assessment of CP system performance data together with an understanding of the true corrosion status of the structure is needed for the identification of any issues which may require immediate rectification and to ensure that the structure is receiving optimum corrosion protection.