氢氟酸浓度对钛合金油管的疲劳行为的影响

Effect of Hydrofluoric Acid Concentration on Fatigue Behavior of Titanium Alloy Tubing

基于Zr-Mo系钛合金(0.6Zr3Mo)油井管在服役过程中因工作环境而导致的疲劳断裂问题,通过应力加载的方式研究了钛合金在不同浓度氢氟酸环境与实验室环境下的疲劳性能,并对其进行比较。结果表明:在70%σs应力幅作用下钛合金在有无腐蚀环境下均呈现循环软化特性;氢氟酸溶液促进了钛合金疲劳裂纹形核并加速了疲劳裂纹扩展速率,缩短了钛合金的疲劳寿命,并且疲劳寿命随腐蚀液浓度的增加呈下降趋势;氢氟酸浓度对钛合金的裂纹扩展方式具有一定影响,在实验室环境下钛合金裂纹扩展主要为周期性解理;在低浓度氢氟酸环境下由于氢氟酸腐蚀形成的二次裂纹容易诱发解理面的形成,裂纹扩展仍以解理的方式扩展;而在高浓度氢氟酸环境下裂纹的扩展方式有所改变,裂纹在韧性区扩展程度增加,以解理形式扩展的程度有所下降。

In terms of the fatigue fracture problems of Zr-Mo titanium alloy(0.6Zr3Mo)oil well pipe caused by working environment during service,the fatigue properties of titanium alloy under different concentrations of hydrofluoric acid and laboratory conditions were investigated and compared by stress loading.Results showed that under the action of 70%σs stress amplitude,titanium alloys exhibited cyclic softening characteristics in both corrosive and non-corrosive environments.The hydrofluoric acid solution promoted the nucleation of fatigue cracks in tita-nium alloys and accelerated the propagation rate of fatigue cracks,which shortened the fatigue life of titanium alloys,and the fatigue life showed a decreasing trend with the increase of corrosion solution concentration.Meanwhile,the concentration of hydrofluoric acid had a certain impact on the crack propagation mode of titanium alloys,and in laboratory environments,the crack propagation of titanium alloys was mainly characterized by periodic cleavage.In low concentration hydrofluoric acid environments,secondary cracks formed by hydrofluoric acid corrosion could easily induce the formation of cleavage surfaces,and the crack propagation still propagated in a cleavage manner.In high concentration hydrofluoric acid environments,the propagation mode of cracks had changed with an increase in the degree of crack propagation in the ductile zone and a decrease in the degree of crack propagation in the form of cleavage.