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℃..
Highlights
As an important means of in-service welding repair, B sleeve repair technology can ensure continuous pipeline transportation, and reduce the degree of environmental damage, shorten the repair cycle and reduce the repair cost [1,2]
The repair technology is applicable to a wide range of defects, including pipeline corrosion, cracks, mechanical damage, weld defects, etc., and can repair leakage defects, with good repair effect and high reliability, which belongs to permanent repair[3,4].When the B-type sleeve is welded, the pipeline is in an uninterrupted state, and there is a rapid flow of pressurized gas or liquid medium in the pipeline, which is difficult to ensure the preheating temperature and interlayer temperature
The pipe body was heated by medium frequency heating method, and the temperature distribution below and upstream and downstream of the medium frequency heating zone was recorded by thermocouple real-time test (Figure 1, the temperature test point number below the heating zone was P1~P16, and the temperature test point number above the heating zone was B1~B16)
Summary
As an important means of in-service welding repair, B sleeve repair technology can ensure continuous pipeline transportation, and reduce the degree of environmental damage, shorten the repair cycle and reduce the repair cost [1,2]. The repair technology is applicable to a wide range of defects, including pipeline corrosion, cracks, mechanical damage, weld defects, etc., and can repair leakage defects, with good repair effect and high reliability, which belongs to permanent repair[3,4].When the B-type sleeve is welded, the pipeline is in an uninterrupted state, and there is a rapid flow of pressurized gas or liquid medium in the pipeline, which is difficult to ensure the preheating temperature and interlayer temperature. The cooling rate of weld is too fast, which will promote the formation of hydrogen-induced crack-sensitive harden structure in welded joints, so hydrogen-induced cracks are easy to occur and the bearing capacity of the joints is reduced. [56].Preheating before welding can slow down the cooling rate after welding, and promote the diffusion of hydrogen, The cooling rate of weld is too fast, which will promote the formation of hydrogen-induced crack-sensitive harden structure in welded joints, so hydrogen-induced cracks are easy to occur and the bearing capacity of the joints is reduced. [56].Preheating before welding can slow down the cooling rate after welding, and promote the diffusion of hydrogen,
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