A two-dimensional physical and mathematical transient heat transfer model for the pipeline with irregular inner geometry boundary is built.The identification problem of pipeline inner boundary is solved by using finite element method and conjugate gradient method(CGM)-based inverse algorithm.The differences of sensitivities of the transient and steady pipeline outer surface temperature to the inner boundary change are analyzed and certified by a series of numerical simulation experiments

in which the influences of temperature measurement errors and initial inner boundary guesses are tested.It is found that the temperature measurement errors and initial inner boundary guesses have no obvious effect on the pipeline inner boundary identification results when the infrared inspection is carried out in the transient heat transfer state

while the accuracy of the boundary identification results is poor with temperature measurement errors when the infrared inspection is carried out in the steady heat transfer state.Therefore

in the engineering application

in order to identify the inner geometry boundary accurately

the infrared inspection in the transient heat transfer state is more appropriate than that in steady heat transfer state.