Ringworm corrosion is caused by the upsetting process, in which the heat required for upsetting creates two different grain structures, one in the upset and another in the rest of the pipe. This condition can be avoided by fully normalizing the pipe after upsetting. To normalize the pipe, heat is applied to change the grains to a uniform structure.
3) Bimetallic corrosion is sometimes found when new pipe is added to old pipelines. The old pipeline covered by oxide and rust is cathodic to the new pipe, thus accelerating the corrosion rate in the new pipe. Another type of bimetallic corrosion is ringworm corrosion.

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