Influence of operation condition on in-service welding temperature field of X80 natural gas pipeline

In order to study the influence law of natural gas transportation parameters on temperature field in the heat affected zone of in-service welding in X80 natural gas pipeline, the X80 natural gas pipeline with a diameter of 1 422 mm and a wall thickness of 25.7 mm was studied and the temperature field during its in-service welding was numerically simulated with the finite element method. The results show that the process of temperature drop from 800 ℃ to 500 ℃ in the heat affected area (with the time required expressed as t_8/5) appears within the depth of 10 mm in the first 20 s of in-service welding. Besides, the natural gas transportation temperature has the greatest impact on the temperature field of pipeline. When the transportation temperature is less than 10 ℃, t_8/5 decreases sharply as the temperature drops, and it is as low as 2.5 s when the transportation temperature is -50 ℃. Further, the transportation pressure and flow rate of natural gas have little effect on t_8/5, and t_8/5 decreases slowly with the increasing of transportation pressure and flow rate of natural gas. When the transportation temperature is less than 10 ℃, the flow rate is greater than 10 m/s, and the pressure is higher than 10 MPa, the heat affected zone and the welds are at a high risk of cold cracks. The research results could provide a theoretical basis for the on-site construction organizations to control the parameters such as the transportation conditions and welding technology for in-service welding of X80 pipeline, which is helpful to ensure the safe operation of in-service welding of X80 pipeline.