Production process for heat exchanger tubes with DLC-type inner coating

The use of DLC-type coatings for mitigating fouling in shell and tube heat exchangers has substantial potential, as DLC is highly resistant to abrasion and known for easy cleaning and minimum fouling. Further development of this technology has hindered, however, by the lack of effective production procedures.
Research at University of Applied Sciences Upper Austria, Wels, Austria (FH OOE) investigates on industrial applications of DLC with shell and tube heat exchangers, using PACVD-reactor technology from RUBIG Group, Austria.
There are two production routes in question: G-route gap-coating for long tubes and C-route cavity coating for shorter, single tube pieces. For C-route coating on the inner side is presented on the basis of 400 and 700 mm tubes, outer diameter 25 mm and 2 mm in thickness made of 1.4571/316Ti. The effect of primary heat resistance of the layer is discussed. Orbital welding was applied to reach final products with a length of about 6000 mm, then tested for its mechanical properties and straightness deviation. Results showed that the coating is approximately 98 to 99% effective at protecting tubes of these dimensions from fouling, leaving only the orbital weld zones uncoated.