Production Process for Heat Exchanger Tubes with Diamond-like Carbon-Type Inner Coating

The application of DLC-type (diamond-like carbon) coatings in shell and tube heat exchangers offers a promising solution to mitigate fouling due to their high abrasion resistance, ease of cleaning, and minimal fouling. However, the advancement of this technology is hindered by the lack of efficient production methods. Research at the University of Applied Sciences Upper Austria in Wels focuses on the industrial use of DLC coatings with shell and tube heat exchangers, utilizing plasma-assisted chemical vapor deposition reactor technology from the RUBIG Group in Austria. Two production approaches are explored: the G-route for gap-coating elongated tubes and the C-route for cavity coating shorter tube segments. This paper examines the C-route coating applied to the interior of tubes measuring 400 and 700 mm in length, with an external diameter of 25 mm and a thickness of 2 mm, made of stainless steel alloy 1.4571/316Ti. It evaluates the coating’s primary heat resistance. To achieve a final product length of approximately 6000 mm, orbital welding was used. The finished products were tested for mechanical properties and straightness deviations. The findings show a high efficacy rate of 98 to 99% in preventing fouling, except in the orbital weld zones.