External Corrosion Direct Assessment (ECDA) is a structured process that improves safety by assessing and reducing the impact of external corrosion on pipeline integrity. ECDAs proactively prevent corrosion defects from growing to a size that would ultimately impact a pipeline’s structural integrity by:

  • Identifying and addressing corrosion activity
  • Repairing corrosion defects
  • Remediating the causes of corrosion




A close interval survey (CIS) is a measurement tool used to ensure pipeline cathodic protection systems are operating. Close interval surveys may also be referred to as close interval potential surveys (CIPS). They are often part of a structured External Corrosion Direct Assessment (ECDA) process.

Close interval surveys are conducted on buried or submerged pipelines. At regular intervals, measurements are taken 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 close interval survey provides insight into the cathodic protection on your pipeline.

  • 2 Direct and alternating current voltage gradient survey (DCVG/ACVG)

Evaluating the pipeline coating with direct and alternating current voltage gradient survey (DCVG/ACVG)

Direct current voltage gradient (DCVG) and alternating current voltage gradient (ACVG) surveys are methods used to evaluate the coating condition of buried pipelines and locate and analyze coating damaged or defects.

Direct Current Voltage Gradient Survey

In a DCVG, a direct current (DC) signal is applied to the pipeline and the voltage gradient in the soil above the pipeline is measured. Voltage gradients, as measured between two calibrated reference electrodes spaced apart, arise as a result of the current pickup or discharge at pipeline coating holiday locations.

Alternating Current Voltage Gradient Survey

Similar to a DCVG survey, alternating current voltage gradient (ACVG) surveys utilize an alternating current signal applied to the pipeline to create the voltage gradient at the location of a coating defects.

Both ACVG and DCVG surveys are known to be more precise in the detection of coating defects over other methods. The DCVG survey is the only method available that can aid in approximating the size of pipeline coating defects.

Qualified PVD Training technical personnel can conduct DCVG and ACVG surveys in the field oil, gas and water pipelines. Data is then analyzed by NACE certified experts.

PVD Training’s mission is to solve your corrosion problems. We are ready to assist with your corrosion engineering and field service needs, including design, manufacturing, installation, commissioning and ongoing maintenance, as well as project management and corrosion control solutions. In addition, we offer a broad range of proprietary corrosion prevention products.

2.3 Pipeline current mapping (PCM)


A Pipeline Current Mapper or PCM is a device used to perform an AC current attenuation survey to qualitatively rank coating quality and highlight pipeline locations with the most significant coating holidays (defects). An AC current is applied to the pipeline and coating damage is located and prioritized according to the magnitude of current attenuation.

AC current attenuation surveys can be performed with impressed current cathodic protection systems energized. When sacrificial (or galvanic) anodes are connected to the pipeline either directly or through a test station, it is recommended that they be disconnected when feasible when performing pipeline coating quality testing to prevent signal loss and enhance current flow down the pipeline.

Qualified PVD Training technical personnel can conduct PCM AC current attenuation surveys to determine pipeline coating quality in the field for oil, gas and water pipelines. Data is then analyzed by NACE certified experts.