Safety Analysis And Welding Repair Simulation Of Ball Of Tee With Crack Of Main Steam Pipe

Ball of tee of main steam pipe is a special kind of structure in the main steam pipeline, it is used to distribute and change the direction of medium in the main steam pipeline, because of the particularity on structure and function, it plays an important role in piping field. In consideration of the importance of ball of tee of main steam pipe in the main steam pipeline and the harmfulness of accident, the method of numerical simulation and safety assessment was adopted in this paper, the safety analysis and evaluation of ball of tee of main steam pipe was conducted under the condition of containing crack and digging out crack, the welding temperature field and residual stress field of ball of tee of main steam pipe was analysed, the coupling analysis of welding residual stress and working load was researched, the conclusions obtained are as follows:(1) The minimum value of Von Mises stress of ball of tee with crack of main steam pipe was 27.3MPa at 550? and 18.4MPa, distributing on outer surface of ball and part area of the outer surface of main pipe; The maximum value of stress at both ends of crack reached 511MPa. Safety evaluation of ball of tee with crack of the main steam pipe was based on GB/T 19624-2004, the failure assessment diagram was consistent with the maximum allowable crack size, the conclusion of ball of tee of main steam pipe was not safe.(2) The minimum value of Von Mises stress of ball of tee with digging out crack of the main steam pipe was 26.2MPa at 550? Cand 18.4MPa, distributing on outer surface of the ball; The maximum value reached 511MPa, compared with the case of containing crack, the amplitude of reduction of stress peak was 45.9%; According to GB/T 19624-2004, the result of safety assessment was safe.(3) Manual arc welding was adopted to repair crack defect, the maximum value of residual stress under the condition of preheating 200? was 226MPa; Under the condition of preheating 250?, the maximum value of residual stress was located at the welding seam and reached 210MPa, compared with preheating 200?, the maximum value of residual stress decreased 7.6%,the residual stress distribution was generally same as preheating 200?, welding seam area was generally symmetrical distribution.(4) The distribution of circumferential residual stress and axial residual stress under two kinds of welding condition at preheating 200? and 250?were generally same, under the condition of preheating 250?, both stress and stress gradient decreased; With the increase of welding current,the maximum value of circumferential residual stress and axial residual stress increased, with the increase of welding speed, the maximum value of circumferential residual stress and axial residual stress decreased; Improving the welding current or decreasing welding speed, the growth rate of axial residual stress was smaller than circumferential residual stress.(5) Under the condition of preheating 200?, the maximum value of coupling stress of residual stress and working load was 292MPa, under the condition of preheating 250?, the maximum value of coupling stress of residual stress and working load was 275MPa. Welding repair of preheating 200? and 250? to ball of tee could ensure safe operation at 550? and 18.4MPa.