Steel pipelines that are buried go through corrosion over time if not given proper protection against corrosion. The rate of corrosion is also faster in soils that are subjected to corrosive elements like saltwater.
The first line of corrosion protection includes protective coatings along the pipe like resin and epoxy which are then usually enhanced with cathodic protection.
As the pipe ages, coatings can deteriorate, this is where appropriate cathodic protection becomes essential in preventing further damage from corrosion. To ensure pipelines are in good condition, companies must carry out surveys to check the coating and cathodic protection are within specified parameters, these surveys include CIPS and DCVG.
CIPS (Close Interval Potential Survey)
A Close Interval Potential Survey (CIPS) assesses the effectiveness of the cathodic protection system on the pipeline. A CIPS is a measurement tool used to ensure the cathodic protection system is operating to specified standards. CIPS may also be referred to as CIS (Close Interval Survey).
Measurements are taken (along regular intervals) of the potential (voltage) difference between the pipeline and a reference electrode in contact with the material or soil (electrolyte). The data collected during a CIPS provides insight into the cathodic protection on the pipeline and ensures the levels are within parameters.
DCVG (Direct Current Voltage Gradient)
A Direct Current Voltage Gradient (DCVG) survey is a type of survey method that is used to assess the efficacy of corrosion protection, particularly on structures buried underground.
The technique is used to trace coating faults (known as holidays) as well as determine the deficits in the methods that are used to control corrosion. This non-intrusive, above ground survey allows the operator to identify the location of any coating defects.
A DCVG survey is considered the most reliable method to measure and trace coating defects in pipelines. It is based on quantifying voltage gradients present in the soil over pipelines that are protected by cathodic protection.
MERLIN Remote Synchronized Interruption
Synchronized interruption is typically required for CIPS (Close Interval Potential Surveys) and DCVG (Direct Current Voltage Gradient) surveys. This enables rectifiers on the same pipeline to synchronize their output and interrupt it according to a precise timing interval.
MERLIN rectifier monitors drive an external 12V relay, which can be electromechanical or solid state. They use GPS to synchronize their clocks and maintain synchronization at all times.
Interruption may be switched on and off, or the cycle changed, from a cell/mobile phone in the field (DX/GX versions only), from the CPSM software or online via iCPSM. Synchronization enables surveys to be carried out more quickly, with no rectifier setup or additional equipment, thus saving time and money.
The option, available with MERLIN Super and Excel rectifier monitors, consists of:
GPS synchronization hardware and firmware (internal to MERLIN)
External GPS antenna (combined GPS/Cellular antenna also available)
External MERLIN Interrupter or mercury relay
Abriox’s MERLIN Interrupter is designed specifically for precise solid state interruption of rectifiers connected to a buried pipeline. It fails safe and switches the rectifier output loads encountered under the temperature, environmental and electrical conditions experienced in a rectifier cabinet.
All MERLIN units automatically maintain precise synchronization with each other, they also provide a link to mapping software for accurate positioning.
The patterns that are supported cater for both CIPS and DCVG surveys. MERLIN interruption is compatible with all industry recognised CIPS and DCVG survey patterns and most portable above-ground survey equipment.
- CIPS surveys usually require the majority of the pattern to be ON to maintain the CP protection of the pipeline
- DCVG surveys are the reverse and usually have a longer OFF than ON so that a short “blip” of ON can be seen by the survey tool
The interrupter settings are specified to a resolution of 0.1 seconds (although the actual pattern precision is 1ms). The MERLIN Interrupter can also be used for switching the rectifier output on and off remotely and for instant OFF potential measurement at the rectifier.
In countries where mercury relays are allowed, these can be used instead of the MERLIN Interrupter and will offer a highly reliable, compact and cost effective solution.
For very occasional use, an electromechanical relay can also be used; however, outputting interrupter patterns is likely to exceed the relay contact life after only a few weeks of continuous use.
For further information, please contact us.