Pipeline integrity inspection
On-site inspection is effective to evaluate the performance of a cathodic protection and to detect coating damages on external surfaces of a pipeline.
Aassessment of corrosion protection can provide life extention of buried pipelines
Corrosion protection compliance is not complete once the cathodic protection system is installed. Pipelines must be inspected at frequent intervals. By different survey methods, coating defects can be detected and the level of cathodic protection confirmed.
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The PCM (Pipeline Current Mapping) survey is performed to qualitatively rank coating quality and highlight pipeline locations with the most significant coating holidays (defects).
PCM (Pipeline Current Mapping) works by applying a very low frequency alternating current (AC) to the pipeline by a PCM transmitter. This current signal escapes from the pipeline where there are defects in the coating, and can be identified from above the ground using a PCM receiver (magnetometer). The PCM receiver also provides a measurement of pipeline depth, current magnitude and direction of the current applied by the PCM transmitter. An A-Frame attachment enables pinpointing of coating faults.
This measurement technique is also well suited for identification of interaction with other structures. You may also want to read about current leakage measurement.
A DCVG (Direct Current Voltage Gradient) survey is an above ground non-intrusive survey technique. The measurement technique detect voltage gradients as a result of current flow in the soil, generally associated with a holiday or defect in the pipeline coating but it is not a measure of the adequacy of the cathodic protection system.
A DC current is impressed, either from the installed ICCP system, or a temporary system. As a result of current flow through resistive soil, DC voltage gradients are created. At locations where there are coating defects, the resistance are lower, resulting higher current flow, and hence increased voltage gradients.
CIP (close interval potential) survey is an electrolytic direct current (DC) potential measurements made at regular intervals to assess the level of cathodic protection on buried pipelines. The potential profile includes both “on” and “off” potentials, and interpretation of the results can include identification of coating defects. This survey procedure can also be used to identify areas affected by interaction.