Application of effective maintenance for CUI (corrosion under insulation) of pipes in chemical plants

It is difficult to find CUI of pipe in chemical plants because the arrangement of pipes in chemical plants is too complex and the susceptible areas for CUI are too large. So, for the purpose of effective management of CUI of pipes, an effort has been made to locate CUI by using operation years, temperature, appearance, and etc. But, the probability to find severe CUI was only a few percent. Recently, the numbers of pipes suffering from CUI have increased due to the long operational period for equipment in chemical plants and the maintenance cost have increased rapidly. If this situation continues, it will become so large of a problem that the competitiveness of production cost will decrease. As a countermeasure for this problem, various steps have been taken to more effectively locate CUI events. This includes analyzing CUI in actual chemical plant environment and examining the actual CUI phenomena by laboratory experiments. These steps have led to an increased probability of finding corrosion by more than 2.6 times and the inspection cost has decreased in half. This paper reports an applied example of new inspection method of CUI.