Test Post and Bond Monitors

Test Post and Bond Monitors 2017-06-14T19:23:21+00:00

Pipeline operators must confirm that pipelines and other buried metal structures such as tanks and vessels, are protected cathodically against corrosion. This can be done in various ways:

In impressed current systems

  • By taking pipe-to-soil 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)
  • By checking sleeves, critical bonds and isolation joints to make sure that the integrity of the pipeline is maintained

In galvanic systems

  • By checking the supply of current from the sacrificial anode to the structure it is protecting

Although not usually taken as frequently as at the rectifier, measurements at CP test points are only spot checks. Again, they only indicate problems well after they have occurred and have no alarm capability.

By contrast, MERLIN CP Monitors provide an immediate indication of CP levels at the important points in the pipeline network. In a well maintained CP system all points should be tested periodically but “key posts” should be monitored more intensively, including:

  • Mid-points, end points and low points on impressed current pipelines
  • Points where pipelines cross and may interfere with each other’s protection
  • Bonds, linking pipelines in a common corridor so that they are both protected equally
  • Isolation joints, ensuring that buried (CP-protected) and above-ground (earthed) structures are electrically disconnected from each other
  • Areas where pipelines are affected by electromagnetic fields from power conduits such as buried or overhead high voltage cables
  • Points that are difficult to access, either physically (terrain) or for other reasons, such as on private land where permission is required
  • Points in hazardous areas or situated at busy roadsides
  • Downstream of compressor stations, where elevated gas temperatures may accelerate the corrosion process

Measurements are taken automatically by the MERLIN CP monitor and data is seamlessly sent in a management report to the system HQ where it is displayed and archived in Abriox’s MERLIN CPSM software or online via iCPSM.

Two types of CP monitor are available; the MERLIN CP Monitor which fits inside an M28 test post or bond box and the MERLIN CP Hemi Monitor which fits invisibly within a stand diameter cylindrical riser post. Because they report to a common software platform, different monitor types can be mixed together in the same network.

MERLIN DX CP Monitors (3G/2G)

The range of MERLIN DX CP Monitors are compact, robust, long-life Remote Monitoring Units (RMU) that monitor cathodic protection levels at a riser/test post. They communicate using SMS (text) messaging over the 3G/2G network. 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 or accessed on-line via iCPSM.

Download the datasheets for the range of MERLIN DX CP Monitors and our other products from our support section


The measurement specification for the range of MERLIN DX CP monitors was drawn up with input from pipeline operating companies and independent CP consultants. It includes all the measurements conventionally taken at test stations, cp posts and riser posts:

Monitoring channels are fully independent. This means that a 2-channel MERLIN can be configured to monitor either two pipe-to-soil inputs (the second input could be a sleeve or foreign pipe) or, if a coupon is fitted, one pipe-to-soil input and an instant OFF input. The MERLIN unit incorporates an internal relay, which is opened just before channel 2 is read.

All MERLIN DX CP monitors measure DC and AC voltages on each channel simultaneously. This has become extremely important as operators now recognise that induced AC on pipelines can have detrimental effects.

If a coupon is fitted at the test post, channel 3 can be used to calculate the DC and AC current by measuring the voltage across a shunt of known value (Abriox can supply suitable shunts and cable assemblies). Once the shunt value and coupon surface area have been entered in the CPSM software, the data can be displayed either as the current in mA or as the current density in A/m².

Another configuration enables the DC potential of an unprotected (“native”) coupon to be monitored. By comparing this to a protected coupon (one that is electrically connected to the pipeline and therefore receives cathodic protection) the effectiveless of the CP system can be verified.

High and low alarms can be set for each measurement channel (for DC and AC values). A MERLIN unit will alarm as soon as a measurement is detected outside the acceptable “window” set by the user.

AC Monitoring

It is now recognised that cathodically-protected pipelines (and other metal structures) may be affected by AC from nearby power lines or traction systems.

This phenomenon is thought to be of particular concern in the case of pipelines with high quality (eg fusion-bonded epoxy) coatings that run parallel to high-voltage overhead transmission lines. There is also evidence to suggest that AC-assisted corrosion can occur below the 15VAC threshold.

Abriox’s MERLIN system has been designed to enable pipeline operators to monitor levels of AC on their pipeline – and to monitor their effect (if any) on the cathodic protection system. The MERLIN CP Monitor measures simultaneous DC and AC levels on all channels.

Learn More

Database Software

Data from MERLIN Monitors is automatically stored and transmitted in a management report to the system HQ where it is displayed and archived in the MERLIN CPSM software (Desktop application) or accessed on-line via the internet based iCPSM.

Monitors can be configured to send their data to two HQs; changes made at one HQ are automatically updated at the other HQ with a full audit trail of all changes made to the system.

  • CPSM (Cathodic Protection System Manager) - PC based database software package for displaying, archiving and exporting data from MERLIN monitors.
  • iCPSM (Internet-based Cathodic Protection System Manager) - Online database software package for displaying, archiving and exporting data from MERLIN monitors.
Learn More

For user manuals, quick start guides and software updates, please visit the support section

Photo Gallery

Contact us for more information on how Abriox remote monitoring systems can improve your network management

Please note: Offices are closed weekends and holidays.