FATIGUE DAMAGE AND REPAIR OF 250 kN PORTAL CRANE IN SHIPYARD

The paper presents fatigue damage analysis and repair procedure that was carried out after the cracks at 250 kN portal crane were detected. After few years of crane service, fatigue cracks occurred at several critical points – bottom of the tower and both legs of portal. Previous attempts of repair by simple welding of cracks were not successful, because new cracks were detected soon after the repair. When cracks reached the critical length, the exploitation of the crane was stopped and detailed analysis was carried out. The results of numerical analysis and strain gauge measurements showed the source of a crack propagation – high stress concentration due to inappropriate design of portal details. FEM models also showed that stress concentration could be reduced by applying the additional stiffeners. Having in mind this fact, critical crane areas were redesigned. Later measurements and examinations showed that this repair was successful – after two years of intensive service new cracks were not detected