What Does Pearson Survey Mean?
A Pearson survey is an above ground survey technique used to detect defects in external coatings of metallic pipelines. It employs an alternating current (AC) signal introduced into the pipeline and compares the potential gradient between two movable earth contacts. It is considered as one of the first successful techniques used to locate holidays and defects in coatings of buried pipelines.
The method was first developed by J.M. Pearson in 1941 and was named after him; variations to this method are also in use.
Trenchlesspedia Explains Pearson Survey
The Pearson survey is carried out by two survey operators separated by 6 to 8 meters, who make earth contact through aluminum poles or metal cleats that are fastened to their shoes. An alternating current of 1000 Hz is imposed on pipelines with thick film coatings or approx. 175 Hz for pipelines with thin film coating, using a transmitter which is earthed and connected to the pipeline.
The receiver is tuned to the transmitter frequency and measures the signal received, which is the potential gradient between the two operators. A change in potential gradient results in a change in the signal intensity, indicating a defect. As the lead operator walks over the pipeline and approaches a defect, there is an increase in the intensity of the signal. The intensity will decrease as the lead operator walks away and will spike again when the rear operator walks by the same defect.
The defect can be pinpointed by reducing the distance between the operators.