富氢环境下管道钢的腐蚀疲劳裂纹扩展模型

Corrosion Fatigue Crack Propagation Model of Pipe Steel under Hydrogen-rich Condition

基于腐蚀疲劳裂纹扩展的基本假设,结合氢的弱键理论和局部塑变理论,对处于富氢(氢气)环境下的管道钢提出了氢脆-钝化-断裂模型。推导得出氢脆型腐蚀疲劳裂纹扩展(HE-CFCP)具有明显应力腐蚀准平台开始的转变应力强度因子(Ktran)表达式。考虑了临界断裂强度因子(Kc)对裂纹扩展的影响,提出了HE-CFCP的亚临界断裂强度因子(Ksc)的概念,并将其作为HE-CFCP准平台结束的应力强度因子。通过比较Ktran和Ksc大小,将(Ksc-Ktran)的差值作为衡量由应力强度因子控制的HE-CFCP准平台发生及准平台区间长度的评价标准。通过对已有管道钢的CFCP实验数据分析,考虑氢致损伤和断裂强度因子的影响,将HE-CFCP曲线划分为四个区域:I-近门槛区域;II-I-Paris区域;II-II-氢完全控制区域;III-快速扩展区域。最后分析了氢致损伤对Paris区域和氢完全控制区域的影响。研究表明:基于裂纹扩展动力学规律导出的裂纹扩展速率表达式对描述HE-CFCP具有较好的通用性。

Based on the basic hypothesis of corrosion fatigue crack propagation,and considering hydrogen-enhanced decohesion(HEDE)theoryandhydrogen-enhancedlocalplasticity(HELP)theory,ahydrogen embrittlement-passivation-fracture model was proposed for pipeline steel in the environment of hydrogen-rich(hydrogen).The expression of the transition stress intensity factor(Ktran)that was used as the beginning of HE-CFCP with obvious stress corrosion quasi-platform was deduced.Considering the effects of critical fracture strength factor(Kc)on the crack propagating the concept of subcritical fracture strength factor(Ksc)that was used as the ending of HE-CFCP with obvious stress corrosion quasi-platform was proposed.By comparing Ktranand Ksc,the difference between Ktranand Kscwas used as the evaluation criterion of the stress intensity factor to control the occurrence and interval length of HE-CFCP quasi-platform.Through the analysis of CFCP tests of pipeline steel and considering the effect of hydrogen-induced damage and critical fracture strength factor,the HE-CFCP curve was divided into four regions:I-near-threshold region;II-I-Paris region;II-II-hydrogen complete controlling region;III-rapid propagation region.Finally,the influences of hydrogen-induced damage on the Paris region and hydrogen complete control region were analyzed.The results show that the expression of crack propagation rate based on the law of crack propagation kinetics has a good generality to describe the HE-CFCP.