升温速率对P91钢管道局部焊后热处理温度场的影响及参数优化

Effect of heating rate on temperature field of local post weld heat treatment of P91 steel pipe and parameter optimization

升温速率是P91钢管道局部焊后热处理的关键参数之一,决定着热处理的效率和质量.文中以Φ575 mm×35 mm的P91钢管道为对象,进行79~479℃/h之间的5个升温速率下的局部焊后热处理试验,并分析升温速率对实际升温时间(管道外壁温度达到稳态的名义升温时间+管道内壁温度达到稳态的滞后时间)、管道轴向和径向温度梯度的影响,然后建立P91钢管道焊后热处理有限元计算模型,优化升温速率参数.结果表明,提高升温速率减小整个管道接头的实际升温时间,可以提高热处理效率.当升温速率小于179℃/h时,提高升温速率明显缩短实际升温时间;当升温速率超过179℃/h时,提高升温速率缩短实际升温时间的作用减小.升温速率的变化对径向温度梯度影响较小,对轴向温度梯度影响则较大.基于轴向温度梯度控制准则和优化计算结果,得到了不同壁厚P91钢管道局部焊后热处理最大升温速率的计算公式,最后提出了工程上快速选取焊后热处理最大升温速率的应用方案.

Heating rate is the key parameter of local post weld heat treatment(PWHT) of P91 steel pipes, which determines the efficiency and quality of the heat treatment.This article takes the P91 steel pipe of Φ575 mm × 35 mm as the object, carries out the local PWHT tests at 5 heating rates between 79-479 ℃/h, and analyzes the influence of the heating rate on the actual heating time(refers to sum of the nominal heating time for the outer wall of the pipe to reach the steady state of the temperature and the lag time for the temperature of the inner wall of the pipe reach the steady state), as well as the influence of the axial and radial temperature gradients of the pipe. Afterwards, the finite element calculation model for PWHT of the P91 steel pipe is established to optimize the heating rate parameters. The results show that increasing the heating rate results in the decrease of the actual heating time of the entire pipe joint, which can improve the efficiency of the heat treatment. When the heating rate is lower than 179 ℃/h,increasing the heating rate significantly shortens the actual heating time;when the heating rate exceeds 179 ℃/h, the effect of increasing the heating rate on shortening the actual heating time is reduced. Furthermore, the change of the heating rate has a relatively small effect on the radial temperature gradient,yet has a greater effect on the axial temperature gradient.Based on the axial temperature gradient control criteria and the optimized calculation results, the optimized calculation formula is obtained for the maximum heating rate of local PWHT of P91 steel pipe with different wall thickness. Finally, an application plan for quickly selecting the maximum heating rate in engineering is presented.