FAQ - Exchanger Tube ID Coating

How Long Does The Coating Process Take?

Curran International can coat the ID of an average size exchanger with 750 tubes, 20 feet long in a five- to seven-day period with a single crew working a single shift.

How Thick is Tube ID Coating?

For cooling water heat exchangers, total Dry Film Thickness (DFT) is 6-10 mils; for condenser tube repair linings, a single coat, or 2-3 mils DFT, has proven effective. 

Can Coating be applied to Used Exchangers?

Yes, used exchangers’ tubes are cleaned to SSPC-SP5 “white metal” standard, and inspected for soluble contaminants. Our phenol epoxy works well to wet-in all crevices and pits, encapsulating the entire ID in a homogenous film. The Coating system has been used for in-situ applications, which provide value during limited maintenance schedules, and are cost-effective compared to traditional methods such as retubing. 

What Quality Assurance Methods are Used?

Curran International follows industry standards for surface prep, ensuring a clean and dry air supply, and NACE procedures for discontinuity “holiday” testing of coating film. Exchanger tube bundles are 100 percent inspected using a low-voltage wet sponge test method.

How Does The Coating Effect Thermal Conductivity?

Over 70% of total heat transfer resistance for heat exchanger tubing is boundary layer fluid film and fouling. Removal of fouling and reduction of boundary layer drag enhances flow profile at the tube wall, increasing heat transfer. Subsequent flow rate improvements also directly increase heat transfer. Heat transfer resistance produced by the thin coating layer (6-8 mils dry film thickness) is well below the foul resistance of heat exchanger design (usually 0.001-0.002). This minimal effect is more than offset by the coating’s anti fouling capabilities, since fouling quickly reduces heat transfer resistance.

History of Small Tubular Coating Technologies

Interior tube coating, as we know it, began in Europe in the mid-twentieth century, using a “flood and drain” method to coat tubes with phenolic materials. This remained the only option until the mid-1980s, when spray applications were first tried.