Banca de DEFESA: Felipe Azevedo Canut

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : Felipe Azevedo Canut
DATE: 30/08/2022
TIME: 09:00
LOCAL: Ambiente virtual TEAMS
TITLE:

Assessment of corrosion‐fatigue degradation of grade R4 steel using an electrochemical‐mechanical combined approach

KEY WORDS:

Corrosion-Fatigue, Grade R4 Steel, Corrosion Potential, Electrochemical Impedance Spectroscopy.

PAGES: 100
BIG AREA: Engenharias
AREA: Engenharia Mecânica
SUMMARY:

The study deals with the combined effect of corrosion and mechanical cyclic stresses observed on mooring chains of Floating Production Storage and Offloading (FPSO) units. Grade R4 steel, commonly used in the production of mooring chains, was used in the experiments. Corrosion-fatigue tests under stress-controlled loading were performed in artificial seawater (3.5 wt.% NaCl) using a corrosion cell developed for this purpose. Fully reversed (R = -1) and tension-tension (R = 0.1) loads were tested. In-air fatigue and no-load immersion tests were also carried out for comparative purposes. The results have shown an acceleration of the failure caused by the corrosive environment when compared to the in-air fatigue. The corrosive environment has an ever-increasing importance towards lower stress amplitudes on the observed corrosion-fatigue life. Periodic corrosion potential measurements were carried out during the experiments and the acquired signals were correlated with the degradation level of the specimen. This technique has proven to be effective in detecting important phenomena, such as pitting formation and crack initiation. Electrochemical Impedance Spectroscopy (EIS) measurements were performed to assess the evolution of the electrochemical system during the corrosion-fatigue tests and the results were compared to non-loaded specimens. After the failure, the specimens were examined in a scanning electron microscope (SEM) and in a confocal microscope. The corrosion degradation on the lateral surface of the specimens was assessed using the corroded area fraction as an index. The microscopic analysis revealed that the application of mechanical loads produces a higher fraction of corroded area when compared to the no-load immersion samples, highlighting the synergistic nature of the corrosion fatigue phenomenon. A higher density of microcracks and pits were observed for the lower fatigue loads while large secondary cracks and few pits were identified for the higher amplitudes. Therefore, the failure of grade R4 steel in the seawater environment could be divided into two regimes: one dominated by electrochemical effects, observed in lower stress amplitudes, and the other dominated by mechanical effects for higher stress amplitudes

BANKING MEMBERS:
Externo à Instituição - WALDEK BOSE FILHO - USP
Externo à Instituição - JOÃO CARLOS SALVADOR SANTOS FERNANDES - ULisboa
Presidente - 1122686 - EDGAR NOBUO MAMIYA
Interno - 1249764 - JORGE LUIZ DE ALMEIDA FERREIRA