A type of bimetallic corrosion. Ringworm corrosion has the shape of a ring and is located a few inches from the pipe upset. The 鈥渞ing鈥?can either be very smooth or have severe pitting.

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 normalising the pipe after upsetting. To normalise the pipe, heat is applied to change the grains to a uniform structure.