Procedimiento de reparación e inspección del rodete Francis de la Central Hidroeléctrica San Francisco mediante sustitución de material de los álabes por insertos metálicos prefabricados.

Abstract

The objective of the current research work is to develop and implement the procedure of repair and inspection of Francis runners at San Francisco Hydroelectric Power Plant by replacing the material of blades through prefabricated metal inserts. It proceeded to characterize the state of the blade material in the receiving state (spectrometry, hardness, metallography and destructive tests), besides the mechanism of wear found in the blades (SEM), to subsequently document step by step all the repair stages, that through the operation of a Specialist Technician in Repair of Turbines has been carried out. In addition, it made a strict quality control in all the stages of repair by means of stenciling, 3D scanning, Non-Destructive Tests (VT, PT, MT and UT) and dimensional control. Later, it evaluated the transformations based on microstructural level of steel ASTM A743 Gr. CA6NM generated in the welding process that combines GTAW and SMAW to determine finally the Optimal Post Welding Thermal Treatment Temperature. It was found that wear erosion by cavitation is the most critical that occurs on the pressure side at the outlet of the impeller blades. In addition, it found a loss of steel toughness due to the hardening of the material by the repairs carried out during the maintenance. It determined that plasma cutting in the ASTM A743 Gr. CA6NM Steel generates 2mm HAZ. Finally, at the microstructural level determined that a PWHT at 620° C generates a homogenization in the size of martensite needles in the three zones of the joint (MB, HAZ and MF). It is recommended to qualify the welding procedure specification (WPS) and inspection procedures through NDT and work together on the certification of personnel from all areas of CIRT to guarantee and ensure good repair practice.