Corrosion Occurs from Outside In

Message: Corrosion often begins outside and moves inside.

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The soil surrounding a conduit can be more corrosive than the water inside the pipe. When this occurs, the pipe will corrode faster on the outside than the inside. By inspecting the inside of the pipe, it may appear to be in good condition, however, the pipe may be brittle due to corrosion on the outside.

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  This picture shows several areas of corrosion, but the pipe looks like it still has some life left to it. However, when it was removed, it was very corroded and brittle.

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  The inside of the pipe shows corrosion, but looks like there is some design life left. The red corroded area is the base of the pipe.

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  This is the exterior of that same pipe. These holes were in the bottom of the pipe, not easily visible with the inspection camera. The entire outside of the pipe was severely corroded. Pipes are corroding from the outside in, so an interior inspection may not always reveal the condition of the pipe.

Note: The content on this page was originally created as part of DamOutletWorks.org (DOWL, 2018). It has subsequently been updated and reformatted as part of the Dam Safety Toolbox.
Revision ID: 3134
Revision Date: 09/15/2022