Pipeline operators must confirm that pipelines and other buried metal structures such as tanks and vessels, are protected cathodically against corrosion. Measurements are taken at cathodic protection Test Stations, CP Posts (also known as Riser Posts), Isolation Joints and Critical Bonds – where it is important to record ON/OFF pipe-to-soil potentials, native coupon potentials and measurements of bonding or interfering currents.
Although not usually taken as frequently as at the rectifier, manual measurements at CP test points are only spot checks, they only indicate problems well after they have occurred and have no alarm capability. By contrast, MERLIN Test Station and Bond Monitors provide an immediate indication of CP levels at the important points in the pipeline network.
Manually collecting and analysing field measurements at test posts and critical bonds is labour-intensive and costly. And (very importantly) they can only be reactive – problems can lie undetected for long periods, during which the pipeline is insufficiently protected.
Alternatively it may simply be that certain measurement points on the pipeline create risks to CP technicians, such as at busy road or rail crossings, or are difficult to access, such as on private land. At these points remote monitoring is very cost-efficient and can improve safety.
Further consideration should be made to monitor the effect of induced AC on the pipeline causing extremely aggressive ‘AC corrosion’. This can cause major problems in a very short time, often sooner than the frequency of manual measurements. Combine this with a very real danger if the AC is too high means monitoring the effect of stray AC currents is critical.
In a well maintained CP system all points should be tested periodically but “key posts” should be monitored more intensively, including: