For corrosion to occur, metal, water and air must be present. For example, a metal chain left out in the rain will develop rust. A transmission pipeline, which is made of steel and typically buried in soil, is exposed to water and oxygen throughout its lifecycle. Without preventive measures in place to protect from these elements, the pipeline will corrode and lose strength through degradation of its metal surface. As an operator of transmission pipelines, we must take the appropriate measures to protect our infrastructure from corrosion. As part of our comprehensive pipeline integrity management program, we employ two preventive techniques to control corrosion: protective pipeline coating and cathodic protection.

How does the protective pipeline coating work?

A protective coating is applied on a pipeline before it is installed as a means of separating the pipeline from its surrounding environment (in the case of our pipelines, the soil). The most common type of protective coating used is epoxy, a paint-like substance that seals the surface of the pipeline and separates it from direct contact with the soil. The coating type and selection also depends on the topography of where the pipeline will be installed. For example, if a segment of pipeline is installed at a water crossing such as a river or stream, a coating reinforced with cement may be required.

How does cathodic protection work?

Cathodic protection is used to enhance the protection provided by the pipeline coating. A piece of ‘sacrificial’ metal that easily corrodes is installed near the pipeline. When corrosion occurs, it is drawn towards the sacrificial metal using a rectifier and cables, leaving the pipeline protected and the sacrificial metal to corrode instead.

How is corrosion monitored on pipelines?

To ensure our pipelines receive adequate protection from corrosion, we conduct two types of surveys on an annual basis along selected segments of the pipeline route.

A Test Tap Survey involves a technician assessing existing test tap stations along our pipeline right-of-way. The technician will take readings at the stations and the obtained data will indicate the level of external corrosion mitigation at the specific test tap locations.

A Close Interval Survey involves a technician trailing a thin copper wire about the size of a human hair along the right-of-way and connecting it to the test tap stations within the survey area. The survey readings will indicate if our pipelines are receiving suitable protection to fully mitigate the effects of corrosion.