These coatings can protect carbon steel pipe from water, air, and corrosive chemicals. With those three elements, as well as time and a certain temperature range, corrosion will occur. The first line of defense is the protective jacketing. The second line of defense is insulation system maintenance. Protective coatings on the pipe provide a third line of defense in the prevention of CUI.
Immersion-grade coatings, which are organic, are becoming widely used to coat and protect pipes that operate at or below 300°F. The reason for this temperature limitation is that above that temperature, most organic coatings thermally decompose. Therefore, immersion-grade coatings are an effective tool up to a 300°F operating temperature. They can be considered a valuable tool on carbon steel pipes. The drawback to facility owners, of course, is that they are a financial investment—one that not every facility has been willing to make when operating on inadequate budgets.
In the article, “Corrosion Under Insulation: Prevention Measures” (Insulation Outlook, October 2007), Dr. Hira S. Ahluwalia describes thermal spray aluminum (TSA) coating in great detail. He points out that TSA coating is effective up to a maximum temperature of 1,000°F, much greater than the 300°F limitation of organic, immersion-grade coatings. This type of coating is reportedly more expensive than the immersion-grade coatings, and some facility owners may not think that CUI prevention is worth the investment.
However, the expense needs to be evaluated financially through a life-cycle cost analysis, considering not just the initial cost of the TSA coating, but also the value of the pipe, its life expectancy, and the financial risks associated with repairing corroded pipes, fittings, and other components. If the facility is to be brought out of service for any extended period of time, offering an opportunity for water to intrude and CUI to occur, then TSA coatings should be considered. Therefore, TSA coatings are a valuable tool to prevent CUI for piping systems that operate at temperatures between 300°F and 1,000°F.
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