A method has been developed for creating diamond-like carbon (DLC) coatings on the interior surfaces of pipes. Newer formulations of DLC coatings have shown resistance to chemical attack in high temperature, high pressure autoclaves tests simulating sour production environments even when the coatings are deliberately mechanically damaged prior to testing. These coating have also been shown to be highly abrasion resistant in standard dry and wet abrasion tests. Thus, DLC coatings may significantly extend component life in abrasive hot sour applications in the oil and gas industry.
INTRODUCTION TO DLC PIPE COATINGS
Sub-One Technology(1) has developed method using plasma enhanced chemical vapor deposition (PECVD) for applying diamond-like carbon (DLC) to the inside of metal piping or tubing.1 The apparatus, shown schematically in Figure 1, uses the pipe itself as the plasma deposition chamber, with DC pulse biasing of the pipe as the cathode to attract the ionized gaseous precursor (acetylene) to the interior of the pipe, forming the coating. The resulting coatings approach diamond hardness, are hydrophobic, and electrically non-conductive. The coating is deposited in multiple layers as shown in Figure 2. The metal surface is first cleaned at an atomic level by sputtering with a mixture of argon and hydrogen.2 A layer of pure silicon is grown on the substrate surface to optimize adhesion of the successive layers of the coating stack. Multiple layers of DLC with decreasing silicon concentrations are grown in succession, with a final layer being pure DLC. The Si-doped DLC layers in the center of the coating stack act as stress relievers.3 The coating stack shown in Figure 2 is 30 m thick.
A Critical Difference between DLC Coatings and Coatings Applied as Liquids
A critical feature that distinguishes DLC coatings from coatings applied as liquids.