Lanzutti, Alex
Produzione e studio microstrutturale, tribologico ed a corrosione di rivestimenti innovativi progettati per massimizzare la durabilità di valvole di testa di pozzo geotermiche [Tesi di dottorato]
The present work was born from a collaboration between Friulco, a company producing valves for energy field applications, Corbellini, producer of thermal spray coatings and University of Udine in the frame of a regional project titled: “Studio di materiali e processi per il miglioramento delle prestazioni delle valvole in presenza di fenomeni di erosione/corrosione”. It is known that the geothermal energy comes out exploiting a hot gases or fluids that contain corrosive agents like CO2 and H2S. Hard suspended particles, which are present in geothermal gases, may additionally cause erosion problems. Moreover degradation may occur due to sliding wear associated to mechanical components in reciprocating movement. All the above mentioned degradation phenomena are really intense on the geothermal well head valves leading to reduction of the service life. The aim of this work is to evaluate both corrosion and wear resistance of thermal spray and composite electrodeposits, which are considered as a reliable alternative to weld overlay coatings. The weal overlay coatings are nowadays used against the corrosion and wear degradation of structural steel. The composite electrodeposits and the thermal spray coatings have been chosen due to their good corrosion and wear resistance. In particular the thermal spray coatings used in this experience, deposited by APS and HVOF tecniques, are: NiCr, stellite-6, WC CoCr, NiCr+WC CoCr e NiCr+ Cr2O3. The composite electrodeposits produced and analyzed are Ni, Ni/µSiC and Ni/nSiC deposited under both DC or PC current at the frequency of: 0,01Hz, 0,1Hz, 1Hz, 10Hz. All the above listed coatings were micro structurally characterized by light optical microscopy, Scanning Electron Microscopy (SEM), profilometer, and, just for Ni/nSiC coatings, RF-Glow Discharge Optical Emission Spectroscopy (RF-GDOES). Micro hardness measurements have been performed on all types of coatings. Wear test have been conducted at ball on disk configuration at both room temperature and 300°C. After the wear tests the tested specimens have been analyzed by SEM in order to determine the wear mechanism and by profilometer to calculate the wear rate. The corrosion resistance has been evaluated through potentiodynamic curves in two different corrosive environments: one simulating the condensation in the geothermal well-head valves and another with high concentration of H2S. The obtained results are necessary to define the coatings which may be deposited on a demonstrator valve which will be tested under real working conditions. The choice of the most appropriate coating system was done based on the results of both tribological and electrochemical tests.
In relazione con
ING-IND/21 - Metallurgia

Tesi di dottorato. | Lingua: | Paese: | BID: TD13053453