Failure of a Truck Mounted Hydraulic Crane

A truck-mounted hydraulic crane had a horizontal thrust bearing with one race attached to the truck and the other to the rotating crane. The outside race of the bearing was driven by a pinion gear, and it is through this mechanism that the crane body rotated about a vertical axis. The manufacturer welded the inner race to the carrier in a single pass. After several years of service, the attachment weld between the bearing inner race and the turntable failed in the area adjacent to the heat-affected zone. The fracture zone where there was the greatest tension was heavily oxidized. In the zone where the bearing was in compression, there was a clean surface indicating recent fracture. Finally, there were areas where the weld did not meet AWS specifications for convexity or concavity. These areas were weak enough to allow fatigue cracks to initiate. Recommendations to prevent reoccurrence of the failure include the use of bolts in lieu of welding, a welding schedule that reduces the propensity of lamellar tearing, and the use of an alloy that precludes lamellar tearing. However, if abuse of the crane was the primary cause of failure, none of these recommendations would have prevented deterioration of the machine to an extent that would have rendered the failure improbable.