Materials Performance

NOV 2017

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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42 NOVEMBER 2017 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 56, NO. 11 COATINGS & LININGS D To improve service life, oxide coatings are deposited on the surface of alumi- num alloy drill pipe for offshore plat- forms by microarc oxidation (MAO) technology. This work focused on an experimental study to determine the effect of cathode voltage on the mor- phology, phase composition, and cor- rosion performance of MAO coatings. It was found that the grains of the coatings become refined and smooth with increasing cathode voltage. Fur- thermore, the corrosion rates of the MAO coatings remarkably decreased with an increase in cathode voltage. Drill pipes are common, important tools used in the drilling industr y. 1 The drill pipes on offshore platforms are subjected to differing loads, stress, temperature, and exposure conditons. 2 At present, steel drill pipes are the most common pipe used for of fshore platforms; however, aluminum alloy drill pipes have many advantageous properties over steel drill pipes, such as a significant reduction in weight, environ- mental benefits, good drilling performance, and thermal resistance. 3 Corrosion, which can adversely affect the pipes' mechanical properties and reduce their service life, is the main failure mode of aluminum alloy drill pipes on offshore platforms. 4 Microarc oxidation (MAO) is a surface treatment technology for applying protec- tive oxide coatings on the surface of valve m etal s. 5 Th ese oxide coatings possess many desirable properties, including high hardness, good wear, and corrosion resis- tance. 6 Recent studies on MAO treatments have focused on the composition of the electrolyte; only a few studies reported that electrical parameters (e.g., voltage, duty cycle, frequency, and current density) have a significant inf luence on microstructure and performance of MAO coatings. 7-9 In this experiment, an aluminum oxide coating was applied to the surface of alumi- num alloy drill pipe with MAO technology to improve the corrosion resistance of the drill pipe on offshore platforms. This work shows the effect of cathode voltage on the morphology, phase composition, and cor- rosion behavior of the MAO coatings. Experimental Procedures An aluminum alloy sheet, GB Grade 2A12, was cut into 15 by 15 by 2 mm sam- ples for the MAO coating experiment. The composition of 2Al2 by weight is at least 92% pure aluminum with 1.5% magnesium, 0.5% silicon, 0.6% manganese, 0.5% iron, 4.1% copper, 0.3% zinc, 0.21% chromium, 0.15% titanium, and 0.1% impurities. The experiment employed 30 kW bipolar MAO equipment, which consists of a bipolar pulsed power supply, electrolytic cell, and cooling system. In this experiment, input voltage was 380 V; anode pulse voltage was 240 V; anode current density was 1,500 A/m 2 ; frequency was 100 Hz; duty cycle was 50%; and oxidation time was 30 min. The stainless steel bath served as the cathode, while the 2A12 aluminum alloy samples were the anodes. Prior to MAO treatment, the surface of the 2A12 aluminum alloy specimens was Microarc Oxidation Coatings on Aluminum Alloy Drill Pipe Yan Shen, School of Naval Architecture and Ocean Engineering, Jiangsu Maritime Institute, Nanjing, China Pra S anta K. Sahoo and Yi P eng Pan, Department of Ocean Engineering and Science, Florida Institute of Technology, Melbourne, Florida, USA

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