Most facility managers, engineers, and maintenance and construction personnel now know that corrosion under insulation (CUI) exists and, left to its own devices, can cause serious problems and even catastrophic consequences.
It is also widely known that the results of CUI are costly. How costly? That is harder to define. Most studies on the topic involve all forms of corrosion and their associated costs without providing the individual cost of corrosion related to insulation.
What is clear, however, is that the cost of corrosion in the United States continues to increase. A study completed in 2001 by a research team of corrosion specialists enlisted by Congress titled, "Corrosion Costs and Preventative Strategies in the United States" reported the direct cost of corrosion to be $276 billion per year, with that number potentially doubling when indirect costs are also considered. Compare this to the first study conducted in 1975, which established the benchmark cost of corrosion at $70 billion. Factoring in inflation, this is actually an improvement if the data are compared to the gross domestic product, with 3.2 percent for 2001 versus 4.2 percent for the 1975 study.
CUI is typically difficult to identify because it lies hidden under insulation material, often until it becomes a serious problem. It is also expensive to inspect for or repair since that usually requires inspection by radiography, ultrasonic or other forms of inspection but in most cases requires the removal of the insulation system. This is especially true if the removal involves material with asbestos. A study done by ExxonMobile Chemical and presented to the European Federation of Corrosion in September 2003 indicated that:
- The highest incidence of leaks in the refining and chemical industries are due to CUI and not to process corrosion;
- Most piping leaks (81 percent) occur in diameters smaller than 4-inch nominal pipe size; and
- Between 40 and 60 percent of piping maintenance costs are related to CUI.
Finally, one of the largest chemical manufacturing companies in the world, E.I. DuPont de Numours and Company, estimates that the direct cost of CUI repairs and replacements well exceeds $10 million per year, which does not include normal preventative maintenance costs and indirect costs like loss of production and revenue. This is especially revealing since DuPont is known internationally as a company with world-class facility engineering, maintenance and workplace safety. Adding to this problem is the accepted belief that industrial facilities in the United States are aging, being operated and maintained by fewer personnel, and funded by reduced budgets.
It can therefore safely be determined that CUI remains a large problem for industry, even if it is not clear exactly how big the problem is today.
For CUI to form there must be two basic ingredients: moisture and warm temperatures. For iron products like carbon steel piping and equipment, oxygen is also needed. To have chloride stress corrosion (SCC) of 300 series stainless steel, there also must be the presence of chloride ions. Obviously, oxygen is fairly easy to find, but, maybe surprisingly, so are chloride ions, which are available in a great number of places from seawater, drinking and process water, and chloride chemical compounds to roadway de-icing salts. The presence of acids, acid gases, and bases like caustics and salts also can create and accelerate corrosion.