Layer | Fill | Outline |
---|
Map layers
Theme | Visible | Selectable | Appearance | Zoom Range (now: 0) |
---|
Fill | Stroke |
---|---|
Collaborating Authors
Results
ABSTRACT Pitting corrosion plays an important role in corrosion fatigue crack initiation and growth in austenitic stainless steels that are subject to dynamic loading in an aqueous corrosive environment. Non-metallic inclusions such as sulfides can lead to preferential dissolution and pit formation. Consequently, the cleanliness of austenitic stainless steels, as measured by levels of sulfides and other types of inclusions, strongly influences the material's susceptibility to pitting corrosion, and correspondingly, its corrosion fatigue performance. However, the synergistic effect of dynamic loading and pitting corrosion on corrosion fatigue is not well understood. In this study, the electrochemical and corrosion fatigue properties of a high-strength CrMnN austenitic stainless steel are tested under as imulated drilling fluid environment. The material’s pitting corrosion resistance has been determined by means of cyclic potentio dynamic polarization tests in 18wt.% NaCl solutions at 80°C. The corrosion fatigue strength was evaluated in a test bench under axial loading. Sulfide stringers on the gauge sections of the fatigue specimens dissolved after exposure to the corrosive environment, leaving elongated microscopic porosities acting as surface defects. The detrimental role of pitting is dependent on the fatigue stress amplitude. A fracture mechanics-based approach is adopted to describe the interactions between pitting, inclusion dissolution and corrosion fatigue.
ABSTRACT During heat treatment surface oxide layers, usually called heat tints, are formed on metallic materials. These oxide layers are composed of elements that have been selectively oxidized from the base metal; in the case of high-alloy materials principally chromium, nickel and iron. On austenitic stainless steels, it is well known that the region beneath the oxide layer is depleted in one or more of the elements that are involved in the scale formation. Consequently, reduced corrosion resistance is expected. It is also known that defects and stresses within the heat tint layer limit their protectiveness. Therefore, heat tint layers are usually removed by mechanical and/or chemical treatments to avoid corrosion issues during service. Nevertheless, the same understanding on heat tints formed during aging of precipitation hardenable Ni-based alloys is still lacking. Ni-based alloys generally have better corrosion resistance than stainless steels and the chemical composition of their surface oxide layers differ from those typically formed on stainless steels. In the present work the effect of heat tints on the pitting corrosion resistance of the Ni-based alloy UNS N07718 has been evaluated by means of electrochemical methods including cyclic potentiodynamic polarization tests and electrochemical noise measurements, and exposure tests in chloride-containing solutions.
- Materials > Metals & Mining (1.00)
- Energy > Oil & Gas > Upstream (0.94)