Development and Evaluation of Corrosion Resistant Alloy Coatings for Inner Surface of Tubes and Closed-end Vessels, 18-R8437
Inclusive Dates: 01/01/13 – Current
Background — The internal surfaces of production pipes and process vessels used by the oil and gas industry need protection from corrosion. Generally, corrosion-resistant alloys (CRA) have been widely used. However, the cost for high grade CRA pipes/vessels can be more than 20 times that of commonly used inexpensive stainless steels (e.g. AISI Type 316L stainless steel, SS316) or carbon steel pipes. Furthermore, the main composition of CRA is Ni and Cr with high quantities of molybdenum and tungsten. The increasing demand and cost for non-ferrous metals also drive increases in the price of CRA pipes, and prices for these materials are expected to rise. Additionally, the strength of CRA pipes is usually unsatisfactory compared to carbon steel. One effective way to bring the cost down for CRA pipes/vessels is to use stainless steel or carbon steel as the body material and apply a CRA coating (e.g. Hastelloy® C-276 alloy) onto the inner surface to add protection for the metal surface. The objective of this project is to develop corrosion-resistant C276 coatings for inner surfaces of pipes and closed-end vessels, and to evaluate the performance of C276 coatings under a high-temperature and high-pressure corrosive environment.
Approach — A cylindrical magnetron sputtering (CMS) technique has been developed at SwRI for depositing coatings on the inner surface of tubular structure and closed-end vessels. The C276 coatings were deposited onto stainless steel tubes and vessels using three different magnetron sputtering techniques: continuous dc magnetron sputtering (dcMS), middle frequency pulsed dc magnetron sputtering (PDCMS), and high power impulse magnetron sputtering (HiPIMS). The samples sectioned from the coated tubes have been evaluated in an autoclave for a NACE MR 0175 Level V environment test with a test period up to 90 days. The fundamental relationships between the process, microstructure and corrosion resistance of C276 coatings on the inner surface have been established. Finally, an optimized coating is applied to the inner surface of a closed-end stainless steel pressure vessel, which will be evaluated using the NACE MR 0175 Level V environment test.
Accomplishments — The new CMS system has been successfully used for depositing C276 coatings on the inner surface of tubular structure and closed-end vessels (Figure 1). The deposited C276 coatings exhibited the same chemical composition as the bulk Hastelloy® C-276 alloy. The C276 coatings with thickness varying from 1 to 20 µm have been deposited using dcMS, HiPIMS and PDCMS techniques. Several key deposition parameters (including the substrate bias voltage, the working pressure and the target power) have been optimized to obtain C276 coatings with dense microstructure, good uniformity, excellent adhesion and smooth surface. A 90-day test in the NACE MR 0175 Level V environment demonstrated excellent corrosion resistance of the C276 coated stainless steel tube as compared to the uncoated one. The corrosion resistance of the coatings strongly depends on the density of the coating, the thickness of the coating, and the incorporated defects in the coatings. These properties can be controlled by selecting proper deposition techniques (between dcMS, PDCMS and HiPIMS) with optimized deposition parameters. Currently, the on-going project is focusing on optimizing the CMS system design to further improve the uniformity and quality of the C276 coatings on the inner surface of a closed-end vessel.