Maximum safe shutdown time of differential temperature batch transportation of crude oil

It is a great challenge to determine maximum safe shutdown time of differential temperature batch transportation of crude oil pipeline, for which there is no accepted feasible method. In this paper, based on the results of numerical simulation, the safety of shutdown is analyzed in view of "restart difficulty". Finally, a simple and easy determination method is derived, which can meet the demands of pipeline running, through a series of theoretical analysis. Theoretically, maximum safe shutdown time is infinite for shutdown time without risks. In contrast, for shutdown time with risks, the shutdown time at which the dimensionless emptying time just goes to infinity is found, and then another shutdown time, which satisfies the criteria, i.e. it is not safe as long as input flow decreases with time in restart procedure, is found near the one determined above. The later is the maximum safe shutdown time. This method is also applicable to ordinary waxy crude oil pipeline.