A novel technique for depositing thick DLC based films on the inside of cylindrical substrates, like pipes, tubes and valves, has been developed. A plasma enhanced chemical vapour deposition (PECVD) technique has been used to engineer and optimize the above mentioned films for maximum coating performance. Of particular importance is the corrosion and wear resistant qualities of these films. Changes in film chemistry, structure and thickness are attributed to the improved corrosion and wear resistance. Details will be given of the corrosion testing which has taken place, such as exposure to HCL (hot and ambient temperature), NaCl and H2S environments. One such test is a very aggressive sour autoclave test where the film is exposed to an aqueous, organic and gas phase over a 30 day period and no damage to the film was found. In depth details of this sour autoclave test will be shown including photographs of the film before and after testing. Wear testing has also been carried out in dry and wet sand slurry environments where very low coefficient of friction (COF) and wear rates were found. It is believed that this thick DLC based film can increase the component life in applications where internal surfaces are exposed to highly corrosive and abrasive media, in particular the oil and gas industry. Examples of such applications are mud pump sleeves, deep well components, directional drilling, abrasive flow spools, pump barrels and in sour fields (H2S).