The efficiency of several fatigue crack retarding methods are described and examined. Al-alloy flat specimens with a central „key hole“ starter notch were tested in a closed-loop servo-hydraulic test machine. After the cracks had propagated to a predefined value, the following crack retarding methods were undertaken: repair welding, welded metal reinforcement, adhesively bonded CFRP patches, single peak tensile overloads and fatigue crack arrest holes. Steel bars with longitudinal welded attachments were also tested in the fatigue test machine, and after the crack propagated to the opposite side of plate, repair welding was carried out, followed with weld toe hammering or grinding. Best fatigue crack retarding methods and repairs are presented and explained. Several fatigue cracks repair procedures and analyses are presented as industrial case studies, such as: the fatigue failures on the ships main engine lateral supports, the fatigue cracks of the large portal crane, the fatigue cracks at the cement mill gear, the Francis turbine rupture, fatigue failures of the rolls with, etc.