Failure investigation and reparation of a crack on the boom of the bucket wheel excavator ERS 1250 Gacko

Bucket wheel excavator ERs 1250 has been in operation for over 30 years in the Gračanica-Gacko mining basin. It is operating in very hard working conditions due to exploiting very solid material, which has adverse effects on the behavior of the whole structure. Bucket wheel excavator boom is a single tube approximately 20 m long. The crack was detected in a cylindrical root of the boom tube at nearly 270° of its circumference. Finite element method was applied in calculations and the first calculation was performed for the complete usage of engine power (the least favorable case), but it didn't indicate the possibility of crack occurrence. Based on exploitation measurements of stress and accelerations, additional simulations of loading were performed (horizontal and vertical unit loads) that could cause the crack. Numerical analysis has shown that the horizontal force causes the initial crack. Measurements and realized loading cycles indicated that the effect of material fatigue is extremely strong. That is why the fatigue is the cause of a considerable crack increase. Based on numerical investigation of the failure, rehabilitation and reparation of the wheel boom were done in the manner as presented in the paper. So, bucket wheel excavator has been operating successfully for a number of years.