海上气田井口管线双相不锈钢焊接接头泄露失效分析

Failure analysis of leakage at welded joints of duplex stainless steel in offshore gas field wellhead pipelines

  • 摘要: 本文针对海上气田井口管线双相不锈钢三通焊接接头处出现泄漏问题开展失效分析,从宏观和微观断口形貌、裂纹扩展路径、微观组织特征、相比例和焊接接头硬度等综合分析了失效原因。研究结果表明,裂纹从管道内壁焊接接头焊趾处起裂,穿过热影响区,向基体母材扩展导致管道泄露,失效原因主要是管道内壁焊接接头焊缝成形不良引起应力集中,加上腐蚀环境,诱发应力腐蚀开裂。焊缝金属组织中形成大量的二次奥氏体,导致奥氏体含量增加,铁素体含量仅为20%,降低了焊缝金属对应力腐蚀开裂的抵抗力。母材组织出现大量的块状沿晶分布的σ相金属间化合物,导致母材变脆,加速裂纹扩展,同时增加了局部腐蚀泄露风险。

     

    Abstract: This article conducts a failure analysis on the leakage issue occurring at the welded joint of a duplex stainless steel tee joint in the wellhead pipeline of an offshore gas field. The failure causes are comprehensively analyzed from aspects such as macroscopic and microscopic fracture morphologies, crack propagation paths, microstructural characteristics, phase proportions, and hardness of the welded joint. The research results indicate that cracks initiated at the weld toe of the pipeline's inner wall weld joint, penetrated through the heat-affected zone, and propagated towards the base material, leading to pipeline leakage. The main failure cause is stress concentration due to poor weld formation in the pipeline's inner wall weld joint, coupled with a corrosive environment, which induces stress corrosion cracking. A large amount of secondary austenite forms in the weld metal microstructure, leading to an increased austenite content and a ferrite content of only 20%, thereby reducing the resistance of the weld metal to stress corrosion cracking. The microstructure of base material exhibits a significant amount of blocky intergranular σ-phase intermetallic compounds, which make the base material brittle, accelerate crack propagation, and increase the risk of localized corrosion leakage.

     

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