Prevention of Erosion-Corrosion in the Field

In planning appropriate and effective countermeasures to protect equipment and machines against the attack of erosion-corrosion, it is indispensable to know the true nature of the attack, so that erosion-corrosion is defined as flow induced localized corrosion in the morphology, and as flow induced macro-cell corrosion in the mechanism. The water chemistry controls mainly the chemical property of the environmental liquids such as pH or dissolved oxygen content in order to prevent uniform corrosion, and accordingly this countermeasure is judged rather not suitable for preventing erosion-corrosion which is categorized into localized corrosion. Selection of material depends not only on the corrosiveness of the environmental liquid but also the circumstances of industry. The cathodic protection, which has been long utilized for preventing the electrolytic corrosion of underground buried pipelines, has a high possibility as a countermeasure to mitigate erosion-corrosion damage because it can be applied to localized corrosion. The elimination of those irregularities in fluid flow, which induce the generation of the macro-cell, is recommended most as a successful countermeasure against erosioncorrosion, and the detailed examples are given. Lastly, methods for monitoring the inception as well as the activity of macro-cell are described. Following the concept of “leak before break” a method to prevent the rupture of the pipeline is also shown.

Keywords: Water chemistry, dissolved oxygen content, cathodic protection, anodic protection, erosioncorrosion, monitoring, macro-cell, electrolytic corrosion, inhibitor, scallop pattern, fish scale pattern, magnetite, hematite.