Influence of internal air flow on temperature field of large diameter and thick wall P92 pipe during local PWHT

A conjugate heat transfer model is proposed based on the Ansys CFX code. The established model which has been verified by experiment is used to simulate the temperature distributions of P92 pipe during PWHT in the case of air flow in pipe with different velocities. The results show that the velocity of air flow in pipe has little influence on the temperature distributions of the outer wall, especially on the weld metal region, but its increase significantly reduces the temperature on inner wall of pipe and rises temperature gradient along the axial direction of pipe. The temperature difference between the inner and outer wall, as well as the axial temperature gradient increases linearly with the increase of the air flow velocity. For each 1m/s increase of the velocity of air flow in pipe, the temperature difference between inner and outer wall will increase by 5.0℃, and the axial temperature gradients on inner and outer wall of pipe increase 0.03 and 0.02, respectively. Meanwhile, the soak band width on inner wall will also be reduced obviously. Due to the influence on the temperature field of pipe during local PWHT of P92 steel, the air flow in pipe should be suppressed, otherwise, it is necessary to increase the width of heating zone.