Abriox

MEASUREMENTS

Standard Measurements

The main measurements of cathodic protection are as follows:

These measurements may be taken at the Transformer Rectifier or, in the field, at CP test posts. However, they are only representative of the pipeline at that point – and for a short length either side.

Close Interval Potential Survey (CIPS)

CIPS fills in the “gap” between measurements taken at test points. A direct connection is made to the pipeline and this trailing wire is unwound from a spool as the technician walks along its length. As he goes, the TR current output is interrupted to enable the technician to take a pipe-to-soil OFF potential measurement at approximately 1m intervals. On pipelines with multiple TRs, all the outputs (or at least those that influence the potential measurement at that point) have to be interrupted synchronously. Interruption cycle times vary but the selected "on" period is longer than the "off" period to limit depolarisation of the pipeline during the survey.

Direct Current Voltage Gradient (DCVG)

DCVG is used for locating and sizing defects in the coating of the pipeline. A coating “holiday” on a pipeline with an impressed current CP system will give rise to a voltage gradient – with the highest gradient closest to the defect. Measurement of the voltage gradient at the surface above the pipeline enables even small flaws to be detected and positioned accurately.

CIPS and DCVG techniques are increasingly used – but can be time-consuming to set up in the field because of the requirement to synchronise transformer rectifier outputs. Abriox’s MERLIN TR Monitor has a remote synchronisation option, using GPS technology, designed to facilitate these surveys. TRs can be configured to synchronise and interrupt their output simply by sending a message from a cellphone.