The properties of duplex stainless steels (DSSs) depend on the ferrite–austenite ratio, on the content of secondary phases and on the contamination with non-metallic inclusions. To assess the quality of DSSs, it is necessary to use an integrated approach which includes controlling for the volume fraction, the morphology and the distribution of all phases and non-metallic inclusions. Samples of several grades of DSSs were obtained using various heat treatments, such as solution annealing and quenching from 1050 to 1250 °C to obtain different amounts of ferrite and to provoke annealing at 850 °C to precipitate σ-phase. As a result, a metallographic technique of phase analysis in DSSs based on selective etching and subsequent structure parameters estimation according to ASTM E1245 was developed. We demonstrated that the developed method of quantitative analysis based on selective etching and metallographic analysis according to ASTM E1245 allows us to obtaining much more accurate results, compared to the point count method described in ASTM E562 and to the XRD method.
The effect of the quenching temperature on the pitting corrosion resistance of lean duplex stainless steel (DSS) were examined. Using thermodynamic modeling of phase formation processes in steel during solidification and subsequent cooling was shown that the equal amount of austenite and ferrite is achieved at 1210°С for examined composition. Experimental steel samples were quenched from 1100 and 1200°С. It was found that as the temperature rises, the pitting potential increases significantly due to the achievement of a favorable phase ratio. The results of this experimental study made it possible to develop a heat treatment that provides high corrosion properties of lean DSS.
This paper presents the results of the study of nickel-based coatings fabricated by cold gas spraying. In this study, compositions based on Ni, Ni–Cu, Ni–Zn, and Ni–Al2O3/TiC coatings applied to low-alloyed steel bases were investigated. The composition, type of powder (mechanical mix or mechanically alloying), and thickness varied to choose the optimal characteristics for recovery, repair procedures, and specific applications in the oil and gas industry media. The second phase was added to Ni-based coatings to increase corrosion and wear resistance. Pure nickel coatings were also studied as a benchmark. Corrosion resistance was studied by means of electrochemical testing and autoclave testing in simulated oilfield conditions. Hydroabrasive resistance was studied using a unique testing bench. Scanning electron microscopy mappings, microhardness testing, and adhesion testing were used to correlate the results of the tests with the structure, continuity, and porosity of the studied coatings. It was shown that applying mechanical alloying of the powder did not lead to an effective increase of corrosion and hydroabrasive resistance. All the studied coating specimens have a sufficiently high adhesion. Ni–Zn coating has the lowest corrosion resistance and high hydroabrasive resistance. Ni–Cu coatings have high corrosion and the lowest hydroabrasive resistance. Al2O3/TiC additives give ambiguous results in the studied properties. A thickness of 40–60 microns provides sufficient performance of the studied coatings. Thus, varying chemical composition and thickness of coatings allows for obtaining the optimal qualities of Ni-based coatings made by cold gas spraying for use in the oil and gas industry.
The paper presents the results of investigation of acoustic anisotropy in industrial alloy made of steel 14HGNDC after hydrogen-induced cracking (HIC) tests according to the standard NACE TM0284-2003. It was found that location and parameters of corrosion cracks with size about 20 microns can be determined by distribution and value of acoustic anisotropy. A quantitative relationship between value of acoustic anisotropy and size of corrosion cracks in the range from 60 to 6600 microns was established. The obtained results have a great importance for improving methods of hydrogen-induced cracking tests and for non-destructive testing of brittle destruction of structures in oil and gas industry by using the acoustodamage method.
The complexity of the operating conditions in oil fields requires the development and use of materials with unique properties. This paper presents the study results for nickel-based coatings fabricated by cold gas spraying. In this study, compositions based on Ni, Ni-Cu, Ni-Zn, Ni-Al2O3/TiC coatings applied to low-alloyed steel bases were investigated. Corrosion resistance was studied by means of electrochemical autoclave testing in simulated oilfield conditions. Hydroabrasive resistance was studied using a unique testing bench. Scanning electron microscopy mappings, microhardness testing, and adhesion testing were used to correlate the results of the tests with the structure, continuity, and porosity of the studied coatings. All the studied coating specimens had a sufficiently high adhesion. The Ni-Zn coating exhibited the lowest corrosion resistance and high hydroabrasive resistance. The Ni-Cu coatings exhibited a high degree of corrosion. The Al2O3/TiC additives gave ambiguous results with respect to the studied properties. Thicknesses of 40–60 microns provided acceptable performance for the studied coatings. Thus, varying the chemical composition the thickness of coatings allows optimal qualities to be obtained for Ni-based coatings made by cold gas spraying for use in the oil and gas industry.
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