连续油管环焊接头的疲劳性能

Fatigue performance of coiled tube ring welded joint

针对连续油管环焊接头疲劳寿命大幅下降(通常只有管体疲劳寿命的20%左右)的现象,采用硬度计、光学显微镜、SEM和EBSD对环焊接头的组织性能进行了分析。结果表明:在热影响区(HAZ)存在一个明显的软化区,该软化区位于距熔合线5 mm左右处,与母材相比,软化区硬度下降8.5%;平均晶粒尺寸由4.9μm增长至8.4μm,位错密度由1.1×10^14m^-2下降为3.3×10^13m^-2,下降了70%,由于位错密度下降使得连续油管环焊接头部分区域强度下降,从而形成软化区,严重影响了连续油管的疲劳寿命。另外,对管材进行焊前热处理,以及在焊接时加速冷却可使环焊接头的软化程度降低,疲劳寿命提高。

Aiming at the sharp decline in fatigue life of coiled tubing ring welded joints which usually only about 30%of the tube body,the structure property of ring welded joint was analyzed by means of hardness tester,OM,SEM and EBSD.The results show that there is a distinct softened zone in the heat affected zone(HAZ),which located at about 5 mm from the fusion line.Compared with the base metal,the hardness of softened zone decreases by 8.5%,the average grain size increases from 4.9μm to 8.4μm.The dislocation density decreases from 1.1×10^14m^-2 to 3.3×10^13m^-2,decreasing by 70%.Due to the decrease of dislocation density,the strength of part of the coiled tube ring welded joint declines,forming a softening zone which seriously affects the fatigue life of coiled tube.In addition,pre-weld heat treatment and accelerated cooling during welding can reduce the softening degree of the ring welded joint and increase the fatigue life.