Abstract
Due to the challenging operational conditions occurring during drilling, e.g., in the oil and gas industry, the corrosion fatigue (CF) behavior of materials used in drillstring components needs to be well understood. The combination of cyclic mechanic loads and a corrosive environment can affect significantly the integrity of a material, which has to be taken into account when selecting and qualifying materials for drilling equipment. Nickel alloys such as the precipitation-hardenable alloy 718 (UNS N07718) are widely used in many industrial applications including subterranean drilling. In the present study, the fatigue and CF behavior of alloy 718 in three different metallurgical conditions was investigated. The CF behavior of the different conditions was determined using customized rotating bending machines enabling testing in a simulated drilling environment at 125 °C. Results have shown that the fatigue and CF strength of alloy 718 is affected by its microstructural particularities, for instance, the amount of strengthening phases and δ-phase.
Highlights
The mechanical fatigue of engineering materials has been extensively investigated.On the other hand, corrosion fatigue (CF) behavior and the mechanisms that rule CF have been less studied
This is quite surprising because CF is one of the most important environmentally-assisted cracking (EAC) mechanisms affecting components subjected to cyclic loading in a corrosive environment
The superior fatigue strength observed for condition 3 is assumed to be related to its microstructural particularities
Summary
Corrosion fatigue (CF) behavior and the mechanisms that rule CF have been less studied This is quite surprising because CF is one of the most important environmentally-assisted cracking (EAC) mechanisms affecting components subjected to cyclic loading in a corrosive environment. The fact that CF has received less attention can be partially explained by the difficulty in simulating accurately cyclic loading conditions and corrosive environments This is true at elevated temperatures, which are usually present in many industrial applications where CF becomes relevant. Service temperatures well beyond 100 ◦ C are common in deep wells creating a very corrosive environment, which in combination with cyclic loading increases significantly the likelihood of CF on metallic materials used in drillstring components
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