Corrosion Behavior of Steel during Repeated Drying and Wetting Cycles under Insulation

In chemical plant equipment, corrosion under insulation (CUI) is sometimes more accelerated than common atmospheric corrosion. In order to simulate this environment, a carbon steel specimen is maintained at 20∼100°C and placed on cotton subjected to repeated drying and wetting cycles ; its corrosion behavior is then examined by measuring the cathodic current density of Pt in relation to dissolved oxygen, in addition to the corrosion weight loss, under potentiostatic-controlled conditions. It is found that the corrosion rate in the drying and wetting cycles is maximum immediately before drying, promoted by an increasing number of drying and wetting cycles, and 8∼20 times that measured in an immersion test. In addition, the rate of corrosion under insulation in actual equipment with insulation is accelerated, particularly in the range of 40∼80°C, because of the relationship between the temperature and the time for drying.