Numerical Simulation And Experimental Study Of The Buried Pipeline’s Temperature Field During The Air-Tight Test

Distributed by buried pipeline is the main method of the gas transportation, and the air-tight of the pipeline should be tested before production in order to ensure the safety during the transportation. During the air-tight test, the initial and final temperature of the test air should be measured accurately to calculate the fixed pressure drop. Actually, the temperature of the pipeline’s outer surface is used to calculate the fixed pressure drop instead of the inside air’s temperature. The calculated result is unreliable and will cause potential security risks during the production of the gas pipeline.Concerning this issue, numerical simulation method was adopted to simulate the temperature field of the buried pipeline during the air-tight test. The minimum time needed for the temperature field of the buried pipeline to achieve stability and the computing formulas of the inside and outside pipeline’s temperature were obtained according to the simulation results, and the air-tight test was conducted to prove the accuracy and reliability of the simulation. Main research results are summarized as follows:(1)The pure conduction model and the heat and moisture transfer model were built respectively. The energy conservation equations and mass conservation equations of the two models were discreted by finite difference method, while the temperature and moisture distribution of the soil around the buried pipeline was simulated according to the discretion result.(2)The simulation results of the pure conduction model and the heat and moisture transfer model were almost the same in different testing temperature and initial humidity. It indicated that the heat transfer and moisture migration in the soil had less influence on the temperature field distribution of the buried pipeline during the air-tight test.(3) The two-dimensional symmetric rectangular model was built with the simplification of the temperature boundary conditions around the buried pipeline. The temperature field distribution and the minimum time needed for the temperature field of the buried pipeline to achieve stability were obtained according to the simulation results.(4) According to the analysis, the temperature distribution and the minimum time needed for the temperature field to achieve stability were main influenced by the thickness of the pipeline. The relation between the inside and outside temperature of the pipeline during the air-tight test was fitted based on the simulation results.(5) In order to verify the accuracy of the simulation results, the air-tight test was conducted in five commonly used pipelines, and the inside and outside temperature of the pipeline were measured and recorded periodically. According to the comparison of the measured and simulated temperature, it was proved that the two-dimensional symmetric rectangular model was accurate in the simulation of the buried pipeline’s temperature field and the formulas fitted from the simulation results were quitely reliable in computing the temperature of the pipeline during the air-tight test. It could improve the accuracy of the air-tight test and minish the probability of misjudgement.