Independent Corrosion Services Limited (IndCorr) has developed a specialised pipeline survey capability, which is able to accommodate the requirements of pipeline operators who require detailed investigations into external pipeline coating condition, levels of cathodic protection achieved on pipelines and associated problems on the pipeline protection system.

The survey techniques offered are:

Close Interval Potential (CIP) Survey

A survey to provide a detailed profile of the potential level along the entire route of a pipeline. The profile can include both 'system ON' and 'instantaneous OFF' potentials and is used to assess the performance of the cathodic protection system, the condition of the pipeline coating system and presence of interaction effects.

DC Voltage Gradient (DCVG)Survey

Using a pulsed dc current on the pipeline, the survey investigates voltage gradients associated with external coating defects, using two earth contact probes and a sensitive centre-zero voltmeter. Severity of defects can be assessed and effectiveness of cathodic protection at the defect determined.

Pearson Coating Survey

A survey technique to detect external coating defects, which employs an ac signal injected onto the pipeline and compares the potential gradient between two mobile earth contacts. At coating defects, increases in voltage gradient occur which are noted and recorded as the survey progresses.

Signal Attenuation Coating (SAC) Survey

An ac signal is applied to the pipeline and this signal will gradually decrease as it leaks to earth through the capacitive and resistive effects of the coating. At coating defects the signal loss will be greater and the survey equipment is used to measure this intensity at selected pipeline locations to determine coating condition.

Each survey technique has its particular attributes, in general Pearson and signal attenuation coating surveys directly examine the external coating, whereas close interval potential surveys investigate cathodic protection levels and thereby provide an indirect report of coating condition. The dc voltage gradient survey is a hybrid approach, as the technique can locate coating defects and is then able to evaluate whether cathodic protection is achieved at that coating defect.

IndCorr are able to advise on survey selection depending on the specific needs of their clients, pipeline/structure details and status of any cathodic protection system installed.