Corrosion under Attic Fan installation Dallas TX (CUI) is the corrosion of piping and vessels that occurs beneath insulation as a result of water penetration. The water can come from rain water, leakage, deluge system water, wash water, or sweating from temperature cycling or low temperature operation such as refrigeration units.
Unfortunately, because the corrosion is hidden under the insulation, CUI tends to remain undetected until the insulation is removed for inspection or when leaks occur. CUI is a common problem across many industries, including refining, petrochemical, power, industrial, onshore and offshore industries.
In 2001, a study commissioned by Congress was completed by a research team of corrosion specialists. The study, titled “Corrosion Costs and Preventive 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.
Another study, commissioned by ExxonMobile Chemical and presented to the European Federation of Corrosion in September 2003 indicated that:
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 required. To have chloride stress corrosion cracking (SCC) of 300 series stainless steel, there also must be the presence of chloride ions.
Obviously, oxygen is abundant and readily available. But maybe surprisingly, so too are chloride ions, which can be found in a wide variety of places from seawater, drinking and process water, and chloride chemical compounds to roadway de-icing salts. The presence of acids, acid gases, strong bases and salts can also create and accelerate corrosion.
Moisture in its many forms can find numerous ways to get under an insulation system. Rainwater is the most obvious method, but there is also flooding of insulation systems in low-lying areas and water from pressurized water wash down or local steam leaks. Water can also come from fire protection sprinkler systems, which can be as bad as any rainstorm.