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
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
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
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.