Metal pipes are widely used in industrial transportation system, but the inner surface of the pipes is easy to be
corroded and not easy to be repaired, which leads to the great economic loss and environmental pollution. In this
paper, the Diamond-like carbon (DLC) coatings was deposited on the inner surface of 304 stainless steel (304SS)
pipes by the hollow cathode plasma enhanced chemical vapor deposition (HC-PECVD) equipped with the direct
current power supply with the pulse frequency of 100, 500, 1000 and 1500 Hz. The aim of this paper is to
improve the corrosion resistance of pipes inner DLC coatings by tuning the pulse frequency. Results indicate that
the sp3-C hybridization content (16.7% ~ 26.7%), the disorder degree of carbon structure and the hydrogen
content of pipes inner DLC coatings all show an increasing trend with the reduction of pulse frequency, while its
stress level presents an opposite trend. Compared with 304SS pipes (0.51 V and 8.94 × 10 6 A∙cm 2), the pipes
inner DLC coatings present more positive corrosion potential ( 0.49 V ~ 0.27 V) and lower corrosion current
density (3.62 × 10 6–4.46 × 10 8 A∙cm 2), better corrosion resistance, which is considerable as an effective
protection coating. The pipes inner DLC coatings deposited at 500 Hz present the lowest corrosion current
density (1.22 × 10 7–4.46 × 10 8 A∙cm 2). Moreover, the corrosion performances of the pipes inner DLC
coatings deposited with the pulse frequency of 500 and 1000 Hz exhibit the better uniformity. Therefore, the
pipes inner DLC coatings deposited at 500 Hz possesses the best corrosion resistance, which can provide
important information for large-scale industrial production in the future.