Abriox

MERLIN CP TEST POST MONITOR

Pipeline operators must confirm that pipelines are protected cathodically against corrosion. This is done by taking DC potential measurements at test posts along the pipe (usually sited at road, rail and river crossings and at field/property boundaries and other rights of way).

Manual measurements at CP test posts are only spot checks with no alarm capability. The MERLIN CP Test Post Monitor is a small, battery-powered unit that can be housed within the test post itself. It monitors and stores voltage (both DC and AC) levels and alarms immediately if a value exceeds user-preset user thresholds. It also has the capability to take instant OFF and current measurements.

Data is automatically stored and transmitted in a management report to the system HQ where it is displayed and archived in the MERLIN CPSM software.

MERLIN is small enough to fit into existing test posts

In a well maintained CP system all posts should be tested periodically but “key posts” should be monitored more intensively. These include:

• Mid-points between rectifiers (the lowest protection level on the pipe)

• Isolation joints where the pipe is connected to above-ground installations

• Proximity to, or crossings of, other pipelines where there may be interference causing reduced voltage levels

• Downstream of compressor stations, where elevated gas temperatures may accelerate the corrosion process

In addition, it is now recognised that AC corrosion problems can be generated by current from overhead power lines or other sources of AC. Stray AC current can cause corrosion “hot spots” leading to rapid deterioration of the pipe wall thickness and very severe financial consequences if the pipeline has to be excavated and re-laid.

The MERLIN CP Test Post Monitor cuts out the laborious manual measurements and provides important operational and environmental benefits. Since many posts are situated at busy roadsides, where parking is difficult and traffic heavy, it also alleviates a significant safety concern.

CP posts at road and rail crossings are a particular hazard