表面机械损伤对CT110连续油管疲劳寿命的影响

Effect of External Mechanical Damage on Fatigue Life of CT110 Coiled Tubing

为了研究表面机械损伤对CT110连续油管疲劳寿命的影响,分别制作CT110连续油管外表面机械损伤试样和表面修磨试样进行疲劳试验,并采用扫描电镜对机械损伤试样断口形貌进行了分析。试验结果显示,外表面机械损伤会造成连续油管疲劳寿命降低,且随着损伤深度增加,疲劳寿命降低越多;其中环向刻槽损伤引起的疲劳寿命下降最严重。机械损伤试样断口扫描电镜分析结果显示,疲劳裂纹起源于外表面机械损伤根部;深度不大于壁厚10%的外表面修磨试样疲劳寿命均高于同深度下的机械损伤试样,且疲劳裂纹起裂于管体内表面。研究表明,对连续油管管体外表面深度不大于壁厚10%的损伤进行修磨可以有效提高疲劳寿命。

In order to study the effect of surface mechanical damage on fatigue life of CT110 coiled tubing,fatigue tests were carried out on CT110 coiled tubing external surface mechanical damage specimens and surface grinding specimens,and the fracture morphology of mechanical damage specimens was analyzed by scanning electron microscopy.The results show that the fatigue life of coiled tubing decreases with the increase of damage depth,and the fatigue life decreases more with the increase of damage depth.The fatigue life decrease caused by circumferential groove damage is the most serious.The results of scanning electron microscopy(SEM)analysis of mechanical damage specimens show that fatigue cracks originate from the root of mechanical damage on the outer surface.The fatigue life of surface grinding specimens with depth less than 10%of wall thickness is higher than that of mechanical damaged specimens with the same depth,and the fatigue cracks initiate on the inner surface of the tube.The results show that the fatigue life of coiled tubing can be effectively improved by grinding the damages whose outer surface depth is less than 10%of the wall thickness.