PRCI PR-151-816

L51608e

Science Applications International Corp.

Need: Gas transmission pipelines are sometimes required to be encased in a larger diameter pipe segment in selected areas, such as under roads or railroad crossings. In time, the casing may become electrically connected to the carrier pipe, either by a metallic short or by an electrolytic path caused by ingress of groundwater through the casing end seals. In the case of a metallic short, the carrier pipe may be shielded from the benefit of the cathodic protection currents. Conventional measurements do not provide an unambiguous indication of the status of the carrier pipe in many situations.

Result: This research project was conducted to develop a suitable method to evaluate cathodic protection on encased pipe sections. The objectives of the research were: (1) to develop techniques to determine whether the casing and the carrier pipe are effectively isolated from each other or if they are shorted together, and (2) to develop a measurement technique which will allow the degree of cathodic protection of the carrier pipe within an electrolyte-containing annulus region of the casing to be assessed if the casing is not shorted to the carrier pipe.

Benefit: The basic measurement concepts were investigated in the laboratory in 1988. The method for isolating the annulus resistance by measurement procedures was also successfully demonstrated in the field using laboratory equipment in 1988. Due to the successful field testing results and the potential user simplicity of the approach, the emphasis for 1989 was placed on the design, fabrication and testing of a demonstration prototype of an instrument to measure the resistance of the annulus region between a casing and the carrier pipe.

Product Details

Published:

12/01/1989

Number of Pages:

82

File Size:

1 file , 570 KB