X80钢焊接残余应力耦合接头组织不均匀下氢扩散的数值模拟

Numerical Simulation of Hydrogen Diffusion in X80 Welded Joint Under the Combined Effect of Residual Stress and Microstructure Inhomogeneity

采用ABAQUS软件建立了煤制气管线X80钢螺旋焊管三维模型,综合考虑焊接残余应力和组织不均匀性的影响,进行了焊接接头氢扩散的数值模拟。结果表明,残余应力和组织不均匀都会导致氢扩散的发生,氢浓度的分布规律与静水应力分布特征相似,即静水应力越高的区域,相应的氢浓度也较高,说明残余应力的影响大于组织不均匀性的影响。氢浓度最高的焊缝区比不考虑残余应力时提高了2.7倍,通过等效充氢压力下的慢应变速率拉伸实验发现,氢脆系数由不考虑残余应力时的18.56%上升至考虑残余应力所致氢富集条件下的32.53%,增加幅度达到75.27%。因此,残余应力是导致焊接接头氢富集进而影响氢脆失效的重要因素,采用数值模拟方法确定氢富集程度则是评估煤制气管线焊接接头安全性的重要基础。

Welded joints of hydrogen-containing coal gas transmission pipelines are prone to hydrogen enrichment due to their severe microstructure inhomogeneity and residual stress in them, and thus lead to the decrease of plasticity and toughness. In order to investigate the effect of local hydrogen enrichment on the safety of hydrogen-containing coal gas transport pipelines, a three dimensional numerical simulation model was established to investigate the hydrogen diffusion behaviour considering the combined effect of microstructure inhomogeneity and residual stress in X80 spiral welded pipeline by using ABAQUS software. Results showed that both microstructure inhomogeneity and residual stress could lead to hydrogen diffusion. The distribution of hydrogen concentration in the pipeline was similar to that of hydrostatic stress distribution. That is, the higher the hydrostatic stress value, the higher the corresponding hydrogen concentration, indicating that the influence of residual stress on the hydrogen diffusion behaviour is greater than that of microstructure inhomogeneity. The enriched hydrogen concentration at the center region of the welded joint with the highest residual stress was 2.7 times higher than that without considering residual stress. Equivalent charging hydrogen pressure was put forward to reflect the degree of hydrogen enrichment in weld metal. Slow strain rate tension(SSRT) tests were subsequently performed on weld metal specimen at equivalent charging hydrogen pressure to investigate the effect of hydrogen enrichment on hydrogen embrittlement(HE) susceptibility. The SSRT tests performed in nitrogen gas and simulated coal gas were used for comparison. The HE index increased from 18.56% in simulated coal gas to 32.53% in equivalent charging hydrogen pressure, increasing by 75.27%. Therefore, the residual stress is a non-ignorable factor, because it could lead to hydrogen enrichment and could significantly influence HE susceptibility in welded joint. The determination of hydrogen enrichment in welded joint by using numerical simulation method is the basis to evaluate the safety of coal gas transmission pipeline.