硫化氢环境中低周疲劳裂纹扩展速率的研究

针对高强钢在硫化氢环境中腐蚀疲劳数据极为缺乏的现状,研究高压气瓶材料4130X在硫化氢腐蚀介质中的疲劳裂纹扩展速率.结合气瓶实际运行的环境和应力状态,应用改进型WOL(wedge-opening-loading)试样,在自行改造的专用低周腐蚀疲劳试验机上,完成0.006 7 Hz超低频率下饱和H_2S溶液、中等浓度H2S溶液和空气三种环境下的腐蚀疲劳试验,并用Paris公式进行两段式拟合,得出da/dN-ΔK的数学表达式.将试样微观断口的变化与宏观应力强度因子K的变化进行对比研究,给出不同环境中三个阶段K值的定量结果.结果表明:相同条件下,H_2S环境中的疲劳裂纹扩展速率比空气环境中大20倍以上;但当H_2S浓度达到一定范围后,对da/dN影响并不按比例增长,浓度相差11倍时,da/dN相差2.4倍,H_2S腐蚀介质的存在加速了疲劳破坏.

LOW CYCLE FATIGUE CRACK GROWTH RATE IN H2S ENVIRONMENTS

Due to the status quo of lack of data about high-tensile steel in H_2S environment, the fatigue crack growth rate of 4130X steel used in compressed H_2S vessel was investigated. Considering its practical operating ambient and stress condition, after overcoming enormous difficulties, the self-modified WOL(wedge-opening-loading) specimens were used in the specifically designed low-cycle corrosion fatigue testing machine, in order to complete the tests under 0.006 7 Hz, in saturated H_2S, moderate concentration and air environment, respectively. Moreover, the mathematical expression of da/dN-ΔK was concluded by the fitted curve using Paris formula. Contrast study between the changes of the specimens' microscopic fracture and the stress intensity factor K was conducted. Therefore, the quantitive result of K of three stages in different environment was determined. The results show that: 1) da/dN in H_2S environment is above 20 times of that in air environment. 2) when the concentration of H2S reaches to a certain range, its effect on da/dN is not scaled up. da/dN differs by 2.4 times while the concentration differs by 11 times. The corrosion medium accelerates the fatigue failure.