Build-up welding is a complex technological discipline that is used to restore worn metal parts to usable condition. To successfully complete this process it is important to know the function of the damaged parts and to have a good knowledge of metallurgy of materials. Also, it important to define the damage and its cause, to correctly repair the damage, and ultimately, to control the repaired parts. Advanced technological processes which are available these days, make it possible to produce steels that are extremely resistant to various types of damage. However, the long-term use of parts made from these materials in unfavourable environments and conditions, still results in wear of the material. This can lead to large economic expenses. The biggest benefit of build-up welding is seen in decreasing of these expenses. This thesis presents an example of build-up welding of the rotor of centrifugal pump used for Flue Gas Desulphurisation process. The manufacturer of the rotor and the pump is Andritz. During the exploitation, the surface of the rotor experienced wear caused by cavitation of the suspension used for desulphurisation. The basic material of the rotor is austenitic - ferrite stainless steel or super duplex steel with DIN number 1.4517. Additional welding material was chosen based on this material. Chosen welding procedure was Flux-cored arc welding (FCAW) in dual shield condition. The welding was obtained respecting the welding parameters specified in the Welding Procedure Specification. During welding, it was important to monitor interpass temperature and to use of welding programs with small temperature input to minimize mixing of additional and basic material. This was important to ensure the correct material structure and to reduce deformation and residual stresses. 3D scanning of the new and damaged rotor was performed prior to welding the damaged parts. With this procedure it was possible to determine the areas where build-up welding should be carried out, the number of passes, or height of the build-up material. After the welding procedure, the rotor was machined to nominal measures. A scanned model of the new rotor was used for machining on CNC milling machine. After machining, the rotor had to be balanced. Finally, the finished product was the repaired rotor that met all the criteria required for its proper operation.