Experimental and numerical analysis of welding of girth welded joints

In the paper the results of welding of girth welded joints of steel pipe API 5L grade X70 (L485M) are presented. GMA welding and two categories of strength of girth welded joints (100-110% and 110-130% of strength of base metal) have been adopted. The weldability tests of base metal as well as numerical modelling for welding process were also carried out. The results of the simulated HAZ confirmed that in the HAZ of the girth welded joints will have high fracture toughness, however, the cooling time t8/5 should be under 10s. Hardness in the simulated HAZ does not exceed 300 HV for real time value t8/5 cooling occurring during welding, which indicates a low tendency to hardening of steel in the HAZ and hence a high resistance to cold cracking of steel. This was confirmed by the Tekken test. Even in the welding without preheating the cracks not occurred in the base metal and HAZ. The hardness was lower than 380HV. Taken into account that the specific cooling time t8/5 has to be lower than 10s during welding API 5L X70 steel the numerical models were prepared in the Sysweld software and verified experimentally. The verification of the numerical modelling confirmed the compatibility of the models. Two welding filler metals were used to weld the preliminary welded joints as well as girth welded joints. The results of mechanical tests of the girth welded joints and the distribution of residual stress in welded joints were also presented. The results indicated that GMA allowed to achieved the proper girth welded joints from the quality and mechanical properties point of view.