Corrosion Under Insulation (CUI) is one of the predominant mechanical integrity issues affecting the ethylene industry. Occurrence can be erratic and sometimes undetectable based on visual examination. Traditional methods of addressing this issue involve selective removal of insulation for visual inspection in carbon steel services that operate from freezing to 300°F. In addition to this recognized range, it is also important to look for areas that are susceptible to CUI due to swing conditions or non-flow areas, even though the design and observed operating condition of the line are outside of this range. This presentation will outline experiences with CUI resulting in leaks in lines listed as operating below 0°F.