X70管道钢在碳酸盐/碳酸氢盐溶液中的疲劳裂纹扩展试验研究

完成了一组X70管道钢预制裂纹试件在碳酸盐/碳酸氢盐溶液中阴极保护条件和3种载荷频率(0.1、1.0、5.0 Hz)下的疲劳裂纹扩展试验。结果表明,在较高的载荷频率下,裂纹的扩展以机械作用为主,高pH值的腐蚀环境的影响不明显;如果载荷频率较低,高pH值环境则会促进裂纹的加速扩展。出乎意料的是,其中有2个试件的裂纹在预裂后停止了扩展,而在裂尖表面出现了蚀坑和开裂,这一现象进一步说明循环载荷可以破坏钝化膜的形成,从而导致表面裂纹萌生。

Fatigue crack growth in X70 line-pipe steel in a carbonate-bicarbonate solution

Fatigue crack growth experiments were performed on a set of precracked specimens of X70 line pipe steel in a carbonate-bicarbonate solution, under condition of cathodic protection and at a loading frequency of 0. 1Hz,1Hz,5Hz. These experiments show that the mechanical factors dominate crack growth at a high frequency, whereas high pH environment accelerates crack growth at a low frequency. Unexpectedly, crack stop growing in two of these specimens. Pitting and cracking occur on the surface at tip of pre crack in the two specimens. The phenomenon further show that cyclic loading damages the passivation film on the surface at tip of pre-crack and then surface cracks initiate.