Abstract
Inadequate design or construction of certain district heating distribution systems has led to severe corrosion problems. These systems were then cathodically protected by means of impressed current installations, and the frequency of leaks was thereby reduced. However, following this, a number of failures due to stress corrosion cracking have been discovered. This has been traced to the alkaline environment round the pipe produced by the cathodic protecion process, combined with subsequent concentration by evaporation, the potential of the pipe then being in the range known to promote caustic cracking when residual stresses are present in the pipe. The only possible solutions to the problem for existing pipelines are either to remove the cathodic protection and revert to the likelihood of general corrosion problems, or to control the applied current so that the pipeline is kept out of the potential range known to promote stress corrosion. In practice this is difficult to achieve and may result in parts of the pipeline being under-protected.
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