Research on Preheating Temperature Field Test of Natural Gas Pipeline in Service Welding under Extreme Condition

Abstract

When the natural gas pipeline is welding in service, the fast flowing medium with pressure in the pipe will take away a lot of heat, and the preheating temperature is not easy to be guaranteed, so it is easy to appear hydrogen-induced crack. In this paper, the in-service welding preheating temperature field of natural gas pipeline under the limit condition of unreduced volume was studied, and the pre-welding preheating test was carried out by using the medium frequency heating method. It is found that the temperature below the heating belt increases gradually with the increase of the intermediate frequency heating power, and the fitting shows a quadratic polynomial gradient. There are differences in preheating temperatures on the same circumference. The highest temperature mostly appears in the direction of 3 point of the pipeline, while the lowest temperature mostly appears in the direction of 0 point, which is related to the tightness of the heating belt, sunshine, blowing and other factors. In addition, the preheating temperature field of the pipeline in service is related to the gas flow in the pipeline. At the same heating power, the downstream temperature of the heating belt is higher than the upstream temperature at the same location, and the closer to the heating belt, the higher the temperature is. When the gas flow rate reaches 9.37m/s and the heating power is 160kW, the average measured temperature at 50mm upstream and downstream of the heating belt of Φ1016 pipeline is 107℃, and the average measured temperature at 50mm upstream of the heating belt is 71℃. When the gas flow rate reaches 8.91m/s and the heating power is 200kW, the average measured temperature at the downstream 50mm of the heating belt of Φ1219 pipeline is 72℃, the average measured temperature at the upstream 50mm of the heating belt is 52℃and the average measured temperature at the upstream 30mm of the heating belt is 71℃..