2015 年 64 巻 12 号 p. 989-996
Corrosion of the inner surface of steel pipes around the insulating joints under cathodic protection not to corrode the outer surface of their buried pipes was experienced for the pipelines of a district heating and cooling system supplying a high-temperature and high-pressure water. In order to prevent such interference corrosion induced by the protection current flowing out to the supplying water, the single insulating joints were replaced by the double insulating joints at both ends of titanium short pipes and the thick steel pipes (STPG) for anodic side. The performance of these countermeasures for 14 years’ service was studied by inspection of materials collected from the field and laboratory tests. The localized corrosion of STPG pipes at anodic site has been suppressed as low for service of 20 years. The titanium short pipe also does not exhibit no distinct corrosion damage at anodic part, nor hydrogen embrittlement at cathodic part. Furthermore, the resistance at insulating joints can be predicted by a simple numerical model based on electrochemical parameters obtained by laboratory tests simulating the behavior of titanium and steel in the high-temperature and high-pressure water.