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CLOSE INTERVAL SURVEYS (CIS)

Above-Ground Pipeline Survey Techniques for Cathodic Protection and Coating Evaluation

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Close interval surveys (CIS) are one of the most powerful diagnostic tools available for evaluating buried pipelines. By collecting pipe-to-soil potential measurements at short, regular intervals along the length of a pipeline (typically every 2.5 to 5 feet), a CIS produces a continuous data trace that reveals exactly where coating defects, corrosion activity, interference, and inadequate cathodic protection are occurring. ICG performs CIS work across the oil and gas, water and wastewater, and transit industries, with AMPP-certified personnel collecting data in the field and senior corrosion engineers analyzing and interpreting the results.

CIS

OIL - GAS - WATER

Why Run a Close Interval Survey? 

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Annual test station monitoring tells you only what is happening at the test station. The pipeline between test stations might have coating damage, interference, or protection gaps that no point measurement will ever catch. A measurement at a test station could indicate adequate protection while a measurement 10 feet away tells a completely different story.

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CIS fills that gap. Specifically, a properly run CIS can identify:

  • Cathodic protection levels along the full length of the pipeline

  • Active corrosion locations

  • Foreign or stray current interference

  • Galvanic corrosion cells

  • Coating damage and holidays

  • The influence of AC grounding or mitigation installations

  • Baseline data for assessing future CP system performance

CIS Methods ICG Performs

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Different projects call for different CIS methods. ICG selects and combines methods based on the question being asked, the pipeline configuration, and what other survey data is available.

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Native / Depolarized Pipe-to-Soil Potential Survey

Used before a CP system is energized on a new pipeline, or to evaluate the 100 mV polarization criterion on an existing system. Provides a baseline for assessing CP system performance after energization.

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"ON" Pipe-to-Soil Potential Survey

Useful where CP current sources cannot be interrupted, such as portions of a pipeline tied to systems serving critical infrastructure. Provides a continuous "on" potential trace without disrupting CP operations.

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"ON/OFF" Interrupted Pipe-to-Soil Potential Survey

The gold standard for CP evaluation. Allows both "on" and instant "off" (polarized) potentials to be recorded by synchronously interrupting all surrounding CP current sources using remote monitoring units. Distinguishes IR drop from true polarized potential and provides the most diagnostically useful CIS dataset.

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What CIS Data Reveals About CP Systems

CIS data is most valuable when it is interpreted in context. ICG uses CIS data to evaluate:

  • Groundbed influence. How current is distributing from galvanic anodes, deep wells, surface groundbeds, and distributed linear groundbeds along the pipeline.

  • Coating performance. Differences in pipe-to-soil response between bare steel, polyethylene, fusion-bonded epoxy, mortar-coated and lined concrete cylinder pipe (MLCP), and other coating types.

  • Coating defect locations. Areas where coating damage is allowing increased current demand.

  • Protection adequacy. Where the pipeline is meeting cathodic protection criteria and where it isn't.

  • Interference signatures. Evidence of foreign cathodic protection systems, electrical shorts, or stray current sources affecting the pipeline.

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AC Gradient Control Mat Assessment

CIS techniques are also valuable for evaluating AC gradient control grounding mats installed at test stations near EHV power lines. These mats are a safety measure that protects field technicians from step and touch potentials while working on buried pipelines in induced AC environments. CIS provides a way to verify that the mats are performing as designed and that the AC environment around the test station is within acceptable limits.

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Coating Applications

ICG has performed CIS work on a wide range of pipeline coating systems, including:

  • Bare steel

  • Coal tar enamel

  • Polyethylene tape and shrink sleeve

  • Fusion-bonded epoxy (FBE)

  • Mortar-coated and lined concrete cylinder pipe (MLCP)

  • Polyurethane coatings

 

Each coating type produces different signatures in CIS data, and accurate interpretation requires field experience with the specific coating system being evaluated.

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How We Work

ICG provides the full CIS workflow, from survey design through final reporting:

  • Pre-survey planning. Coordinating with the pipeline owner on access, valve operations, CP current source interruption, and crew safety.

  • Field data collection. AMPP-certified field personnel collect the data using calibrated equipment and documented procedures.

  • Data processing and quality control. Removing artifacts, identifying anomalies, and validating against test station data.

  • Engineering analysis. Senior corrosion engineers interpret the data and develop conclusions.

  • Reporting. Clear graphical presentation of the data alongside written findings and recommendations.

 

We pride ourselves on accurate data, clean graphics, timely reporting, and working closely with utility staff at every level of the organization.

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