CT80连续油管焊接接头的电化学腐蚀行为研究

Study on Electrochemical Corrosion Behavior of Welded Joint of CT80 Coiled Tubing

采用光学显微镜观察了CT80连续油管焊接接头母材、热影响区（HAZ）和焊缝的显微组织;采用动电位极化技术和电化学阻抗谱测试方法研究了焊接接头各区域在3.5%Na Cl溶液中的电化学腐蚀行为。结果表明：CT80连续油管母材的显微组织为细小的铁素体＋珠光体;焊缝的显微组织不均匀,焊缝中心晶粒细小,两侧晶粒粗大;热影响区的显微组织为魏氏体组织。在3.5%NaCl溶液中,CT80连续油管焊接接头各区域的热力学稳定性顺序依次为HAZ〉母材〉焊缝;HAZ区的极化电阻最大,腐蚀速率最小,耐蚀性最好;焊缝的极化电阻最小,腐蚀速率最大,耐蚀性最差;CT80连续油管焊接接头各区域耐蚀性的顺序依次为HAZ〉母材〉焊缝。

The microstructure of the base metal, HAZ and weld seam of CT80 coiled tubing welded joint were observed by optical microscope. The electrochemical corrosion behavior of each area of welded joint in 3.5%NaCl solution were investigated by the potentiodynamic polarization and electrochemical impedance spectroscopy. The results show that the microstructure of base metal is ferrite and pearlite. The microstructure of weld seam is uneven, the grain in weld center is fine and the grain at both sides is coarse. The microstructure of HAZ is widmanstatten structure. The thermodynamic stability of each area of welded joint of CT80 coiled tubing is HAZ〉base metal〉weld seam in 3.5% NaCI solution. The polarization resistance of HAZ is the biggest, the corrosion rate is the smallest, the corrosion resistance is the best. The polarization resistance of weld seam is the least, the corrosion rate is the largest, the corrosion resistance is the worst.The order of corrosion resistance of each area of CT80 coiled tubing welded joint from big to small is HAZ〉 base metal〉 weld seam.