pH Cell Mitigation and Field Trial of New Coatings
* What are the problems in regards to repairing and preventing corrosion where exposed steel pipe (buried or above ground) enters or exits a concrete encasement?
Need and Benefit
A main goal of Reclamation is the conveyance of water. Pipelines used for this purpose are often partially encased in concrete at some point along their length, particularly when near or part of the dam itself. It has been observed at multiple sites with a variety of environments that pipelines exhibit corrosion preferentially at the location where the pipeline enters or exits a concrete encasement. At the Reclamation Facilities Review in Colorado Springs (April 25th, 2006), it was agreed by all of the participants this is a Reclamation-wide problem, and has been observed both on buried and above-ground pipes.
The corrosion is caused by a pH cell, because the pH inside the concrete is about 12-14, while the exposed pipe is in an environment with a pH of around 7. In addition, there could also be a gap between the concrete and the pipe at the interface which could lead to crevice corrosion and an oxygen concentration cell. In either case, there exists a difference in the potentials for each region; therefore, corrosion will occur at the interface.
This is a common Reclamation-wide problem for which there is no specific solution other than the continual maintenance of the pipelines. Repairs or--in extreme cases--replacement of this area is difficult and expensive due to the concrete encasement, particularly if the pipe is buried. These costs include material and labor, but most importantly down time required to repair the corroded region.
The benefit of this research will be to define the extent of the problem within Reclamation. At that point we can address the best methods to solve the problem, looking for inexpensive and simple solutions that can be applied Reclamation-wide.
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