Pearson coating survey

Principle of survey

The Pearson survey is used to detect coating defects on buried pipelines. The technique employs an AC signal injected onto the pipeline and compares the potential gradient along the pipeline between two mobile earth contacts. At coating defects increases in voltage gradient occur which are noted and recorded on record sheets as the survey progresses.

Site equipment

Transmitter to provide 10 kHz signal.

Receiver tuned to the transmitter frequency, hand held with meter and audio alarm (via headphones)

Earth contacts EL 02 Step probe.

Earth spike and connecting cables for transmitter.

Survey procedure

Initially one terminal of the transmitter is electrically connected to the pipeline usually via a cathodic protection test lead, the other terminal is connected to earth; transmitter is then energised.

In order to ensure the pipe is surveyed accurately the route should be located and marked prior to starting the actual survey.

The EL 02 step probe can be handled by one operator, who also carries the receiver. The operator walks along the pipe route, putting the probe every 2 m in the soil. When the operator approaches a coating defect an increase in the signal level will occur. The level will drop to a clear minimum when the probe is directly over the defect. The signal will increase heavy if the probe is placed further along the pipeline. When the probe is moved along, the signal will decrease gradually. The defect is then recorded by measurement from a reference point, marked on the alignment sheet and/or marker stake placed in the ground.

Data obtained

The information obtained is related to the increase and drop in signal level occurring at possible coating defect locations. This information can be quantified by the operator interpretation of intensity and rate of increase of signal from indications on the signal meter or from the audio alarm. These interpretations can then be used to grade coating defects located.

Processing and presentation of data

Locations of high signal intensity are recorded with reference to a fixed point, marked on the route alignment and/or a stake placed in the ground.

Comments on signal intensity and increase in signal intensity should be recorded, although there will not necessarily be a correlation between intensity and defect size/type on different pipelines and even in different areas on the same pipeline.

Manpower and Vehicles

Only one person is required to carry out a Pearson survey, with a second person being useful to locate the pipeline ahead of the survey, to measure the distance to reference points from possible defects and replace the transmitter. One vehicle should be enough to work efficiently.

Advantages of the PEARSON survey

• Locates all coating defects and foreign metallic objects close to the pipeline that can cause a potential gradient in the soil.

• The entire pipeline section is walked, enabling an inspection of the "right of way" to be carried out at the same time.

• One person can conduct survey.

• Survey technique can provide an assessment of coating condition over paved areas when special pads are clicked on the probe.

Our experienced inspectors are well trained to analyse the gathered data and prepare a detailed report, which includes recommendation for corrective actions, or need for further detailed investigation.
They work fully compliant to our extensive Standard Operating Procedures and our safety manuals.

Please send us attached information request if you want to receive more information on our services and/or used equipment.
If you want to receive a standard offer you can send us attached request for proposal.

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