Equipment

GPS current interrupters are used during cathodic protection (CP) surveys to synchronously switch/interrupt CP current sources, such as transformer rectifiers.

When surveying a structure, several rectifiers, bonds or drainage points may influence the measured structure-to-soil potential. GPS timing allows interrupters installed at different locations to follow the same switching cycle simultaneously.

This is important because it enables survey engineers to:

• Measure ON potentials while the CP system is operating

• Measure instant-OFF or polarised potentials immediately after interruption, before the structure begins to depolarise

• Reduce the effect of voltage drop through the soil, giving a more representative indication of the polarised potential

• Synchronise multiple CP current sources across a large pipeline network

• Produce consistent and repeatable CIPS and DCVG survey data

• Identify areas of inadequate or excessive cathodic protection more reliably

• Reduce manual switching and improve field efficiency

GPS provides a highly accurate common time reference, so all interrupters switch together even when they are installed many kilometres apart.

GPS-enabled CIPS equipment is used during Close Interval Potential Surveys to record accurate, time-synchronised pipe-to-soil potential measurements together with their precise location along the pipeline.

The GPS performs two important functions:

• Timing: It synchronises the CIPS equipment with GPS current interrupters connected to transformer rectifiers and other CP current sources. This allows the equipment to distinguish correctly between ON and instant-OFF potentials.

• Positioning: It records the geographical location of each measurement, creating an accurate potential profile along the pipeline route.

GPS CIPS equipment helps engineers to:

• Capture ON and instant-OFF potentials at the correct point in the interruption cycle

• Reduce errors caused by missed or incorrectly identified switching periods

• Synchronise measurements across large pipeline networks

• Record the position of potential readings accurately

• Identify areas of inadequate or excessive cathodic protection

• Compare results with previous surveys

• Relocate areas requiring investigation or remedial work

• Produce consistent, repeatable and geographically referenced survey data

In simple terms, GPS CIPS equipment ensures that each measurement records both the correct potential at the correct time and the exact position where it was taken, improving the accuracy and reliability of the survey.

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You would not use varnished—or enamelled—copper wire for a seawater trailing-wire cathodic-protection survey because its coating is not designed for that environment.  The thin coating can crack or scrape off while being deployed over rocks, shells or the seabed.  Small coating defects expose copper at random locations, creating unpredictable electrical contact points and unstable readings.   Conventional varnish may deteriorate, detach and leave persistent material in the marine environment.  The wire has limited mechanical protection and can break easily during survey.

For an inshore trailing-wire survey, we use a purpose-designed cable with known electrical characteristics, adequate tensile strength and abrasion resistance. Using biodegradable survey cable allows the coating to breakdown leaving the natural copper to return to the earth.