While inline cathodic protection (CP) current mapping is not necessarily a new technology, it has not been available to corrosion professionals for several years. It has recently been reintroduced for commercial use in liquid pipelines. The body of corrosion professionals needs to be made aware of the unique advantages that Inline CP current mapping offers in certain applications. This technology directly and continuously reads voltage drop in the pipeline wall that is created by the flow of CP current returning to its source. These voltage drops are then converted to current values using a simple Ohm's Law calculation. The resulting current values are then plotted against pipeline footage to create a map of all the current pickup, flow direction, and magnitude for the pipeline. This map reveals all sources and drains of current, provides a visual representation of all current flow to and on the pipeline, and allows changes in current density to be readily identified and measured.
This paper will present several applications where inline CP mapping provides clear, easily understood information to help operators understand and mitigate pipeline CP issues.
Inline cathodic protection current mapping is a unique method of assessing a pipeline's cathodic protection. This is accomplished by measuring the actual current received by the pipeline continuously along the entire pipeline length. Unlike pipe to soil potentials, which can have a great deal of error in them due to forces often beyond our control, the CP mapping tool uses the physical properties of the pipe itself to measure the CP current. The pipe is a very stable part of the circuit, unlike the soil surrounding it. In a CP mapping inspection, there is no need to interrupt current sources and drains to eliminate IR drops that cause potentials to be erroneous. CP mapping inspections are conducted with all current sources and bonds in their normal day to day operating mode.