强制冷却对连续油管对接接头热影响区软化的影响

Effect of Forced Cooling on Softening of Heat Affected Zone of Coiled Tubing Butt Joints

连续油管对接焊过程中易出现热影响区软化。为减小软化对接头性能的影响,开发了强制冷却装置以降低软化程度和软化区宽度。研究结果表明,软化发生在不完全相变区,该区部分针状铁素体转变为多边形铁素体,同时原始的带状组织中M-A组元等转变为板条贝氏体。当热输入为5、7、10 kJ/cm时,若不采取强制冷却措施都会出现热影响区软化。5、7 kJ/cm热输入条件下,强制冷却水流量分别为4、7 L/min可以消除软化现象,而10 kJ/cm热输入条件下,采取强制冷却并不能完全消除软化现象,但可以降低软化宽度及软化程度;在相同热输入条件下,随着强制冷却水流量增大,热影响区宽度减小,热循环峰值温度下降。

In the process of butt welding of coiled tubing, heat affected zone is prone to softening. In order to reduce the influence of softening on joint performance, a forced cooling device has been developed to reduce the softening degree and softening zone width. The results show that the softening occurs in the incomplete phase transition zone, in which part of the acicular ferrite transforms into polygonal ferrite, while the M-A constituent in original band structure transforms into lath bainite. When the heat input is 5, 7, 10 kJ/cm, if the forced cooling measures are not taken, the heat affected zone softening occurs. Under the heat input conditions of 5 kJ/cm and 7 kJ/cm, the forced cooling water flow rates are 4, 7 L/min respectively,the softening phenomenon can be eliminated, and under the condition of 10 kJ/cm heat input, forced cooling can not completely eliminate the softening phenomenon, but can reduce the softening width and softening degree. Under the same heat input condition, the width of the heat affected zone and the peak temperature of the thermal cycle decrease with the increase of forced cooling water flow rate.