The Maximum Solderable Heat Input Simulation Of Different Grade Pipeline During In-service Welding And Database Established

In-service welding technology is an on-site maintenance and emergency repairing technique for operating pipelines which features environment protection,economic,high efficiency.Compared with the conventional oil and gas pipeline repair way,in-service welding can not only ensure continuous transport capacity of pipeline,but also effectively seals pipeline leak.Therefore,the in-service welding technology has a broad application prospect,and can bring huge economic benefits.In this paper,studied by SYSWELD and MATALAB,from the perspective of equivalent strength,a single volume defect under ambient temperature represented the welding pool calculated from the results of the simulated temperature field.Based on a certain material,wall thickness and pipe diameter under different heat input,the change regularity of welding thermal cycle,pipe inner surface temperature,size of equivalent defect and pressure-bearing capacity of pipeline were analyzed.To find out,quantitatively and qualitatively,the impacts of heat input,wall thickness,medium,medium velocity and welding process parameters on the size of equivalent defect.Using MATLAB to multi-parameter numerical fitting,sensitivity mathematical equation between the size of equivalent defect and the above factors was obtained.As the increase of the grade of pipeline and pipe diameter,the size of equivalent defect increases.As the increase of wall thickness,the depth of equivalent defect increases,but the length of equivalent defect decreases.The size of equivalent defect decreases with the increment of welding speed under a certain power,meanwhile,the size of equivalent defect increases with the increment of power under a certain welding speed.Only using heat input to judge the size of the defect equivalent,it is not accurate.In some cases,the heat input of some technological parameters is large but power and welding speed are relatively small can obtain a smaller equivalent defect,compared with heat input of some welding process parameters is small but power and welding speed are relatively large.Based on pipeline safety pressure calculation formula of single volume defect,under the conditions of the certain material,wall thickness,pipe diameter and welding process parameters,the safety work pressure value of in-service welding was obtained.The influencing factors were investigated with orthogonal experimental design,showed that wall thickness has the most significant influence on safety work pressure of in-service and the second is the pipe diameter.What more,in these four factors,the influence of heat input is smallest.That is to say,an appropriate heat input value can effectively avoid burning through when pipe structure parameters are determined.Use Visual Basic 6.5 software to design the in-service welding safety evaluation system of oil and gas pipeline.This system could analysis the safety work pressure value of in-service welding under different structure parameters and welding process parameters through mathematical equations of equivalent defect size and the pipeline safety pressure calculation formula of single volume defect.The system could be carried out to judge burn through of thinwall pipeline,to reduce repeated calculation of finite element analysis and found a higher platform for follow-up study.