Effect of repair times on mechanical properties of X80 pipeline girth weld

Through welding thermal simulation combined with finite element numerical simulation, the same area of X80 girth weld was simulated for several repair times, and changes of microstructure, toughness, hardness and pressure bearing capacity of girth weld after different repair times were studied. The results indicated that microstructure type of welded joint did not change under different repair times. Effect of multiple repair on microstructure was superimposed. The effect of welding heat input made grains recrystallized and refined, which had an optimization effect on toughness. However, with repeated action of thermal cycle, the refined grains began to grow up again and toughness became deteriorated after three times of repair. Weld repair significantly reduced hardness of welded joints and increased dispersion of hardness distribution, and multiple repair slightly improved hardness of welded joints on the basis of the first repair. Under the internal pressure condition, high value of equivalent stress of girth weld after repair was distributed in the filler weld, and stress increased with the increase of repair times. Pressure bearing capacity of girth weld decreased significantly after the first repair, and then decreased slightly with the increase of repair times. Considering strength, toughness and pressure bearing capacity, it was recommended that repair times of girth weld of X80 pipeline should not exceed two times.