Marine Corrosion Performance of Copper Alloy UNS C69100

• Published in: NACE International Corrosion Conference Proceedings pp. 1 - 15
• Main Authors: Nie, Mengyan, Zbihlyj, John, Wharton, Julian A
• Format: Conference Proceeding
• Language: English
• Published: Houston NACE International 01.01.2017
• Subjects: Alloys; Ammetry; Aqueous solutions; Circuits; Copper base alloys; Corrosion potential; Corrosion resistance; Corrosion resistant alloys; Crevice corrosion; Electrochemical impedance spectroscopy; Electrode polarization; Electrodes; Localized corrosion; Marine corrosion; Marine environment; Materials selection; Nickel base alloys; Offshore drilling rigs; Offshore platforms; Optical microscopy; Scanning electron microscopy; Seawater; Silicon carbide; Sodium chloride; Spectrum analysis; Stainless steel; Submerging; Superalloys; Test procedures; Tubes

In order to gain an in-depth understanding of the marine corrosion performance of this alloy, electrochemical test methods including open-circuit potential, electrochemical impedance spectroscopy, potentiodynamic polarization, and zero-resistance ammetry were used for corrosion investigation of UNS C69100 in a 3.5 wt.% sodium chloride aqueous testing solution, in combination with optical microscopy and scanning electron microscopy. UNS C69100 tubing was reported to have best localized corrosion resistance among six metallic materials (316L, Alloy 825, 317LMN, 254 SMO, Alloy 625 and UNS C69100), judged by crevice corrosion and pit depths when exposed to a cyclic salt fog environment (ASTM D 5894 - alternating 1 h wet and 1 h dry conditions, with temperatures varying between 35 °C and 45 °C).1 In the same report, eight alloys (316L, 317 LMN, Duplex, 254 SMO, Alloy 825, Alloy 625, Alloy 400 and UNS C691o0) underwent field trials on two offshore platforms for one year. In order to gain a more comprehensive understanding of the UNS C69100 corrosion performance in marine environments, a series of short term electrochemical tests including open-circuit potential (OCP), electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, and zeroresistance ammetry (ZRA) were used to investigate the single metal and galvanic coupling behavior of wrought UNS C69100 bar and seamless tubing against six alternative alloys (UNS S31603, UNS S31254, UNS S32750, UNS N04400, UNS N08904 and UNS C36000) in a 3.5% sodium chloride (NaCl) solution for 30 days immersion, in combination with optical microscopy (OM) and scanning electron microscopy (SEM). EXPERIMENTAL PROCEDURE Electrochemical Test Procedures Three different electrochemical techniques, OCP, EIS and potentiodynamic polarization were used to characterize the corrosion behavior of the wrought UNS C69100 bar and seamless tubing (designated hereafter as disc and tube samples, respectively) in a 3.5% (wt.%) static NaCl aqueous solution (pH 7.4, and 7 ppm dissolved oxygen concentration).