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Abstract

The objective of this work lies in the three-dimensional study of the thermo mechanical behavior of a blade of a centrifugal compressor. Numerical modeling is performed on the computational code "ABAQUS" based on the finite element method. The aim is to study the impact of the change of types of blades, which are defined as a function of wheel output angle β 2, on the stress fields and displacements coupled with the variation of the temperature.

This coupling defines in a realistic way the thermo mechanical behavior of the blade where one can note the important concentrations of stresses and displacements in the different zones of its complex form as well as the effects at the edges. It will then be possible to prevent damage and cracks in the blades of the centrifugal compressor leading to its failure which can be caused by the thermal or mechanical fatigue of the material with which the wheel is manufactured.

Abstract

The wastewater of petroleum refineries consists of various corrosive pollutants that are harmful not only for human and living organisms but also for the equipment and materials exposed to it. The galvanic corrosion of carbon steel in MgCl2 solution as a pollutant in petroleum refinery wastewater was studied under concentration cell formation. The influence of different operating parameters on the galvanic corrosion established by concentration cell was studied, and the concept of concentration cell corrosion was examined and discussed versus experimental results. The effects of some operating conditions on the galvanic behavior, such as the concentration of MgCl2 (0–2500 ppm) and solution flow velocity (150–1000 rpm), on corrosion rate, corrosion potentials, and corrosion current were investigated. New findings regarding the effect of corrosive substance concentration and the hydrodynamics on the corrosion rate of each electrode and the galvanic current were reported. It was found that the corrosion rate of carbon steel in both cell poles increases with increasing MgCl2 concentration in both free and galvanic corrosion. Increasing MgCl2 concentration also led to an increase in the galvanic currents and the corrosion rate of the two electrodes. The flow velocity in either cell terminal considerably influences the potentials, corrosion rates of both electrodes, and the galvanic current passing in the cell. A high flow velocity in the compartment with the more negative potential caused polarity reversal on some occasions.

Abstract

Microstructural changes that result in relevant improvements in mechanical properties and electrochemical behavior can be induced using different sintering conditions of ASTM F75 cobalt alloys during their processing using powder metallurgy technique. It has been observed that the increase in carbon and nitrogen content improves corrosion resistance and mechanical properties as long as the precipitation of carbides and nitrides is avoided, thanks to the use of rapid cooling in water after the sintering stage. In addition, the reduction of the particle size of the powder improves hardness and resistance to corrosion in both acid medium with chlorides and phosphate-buffered medium that simulates the physiological conditions for its use as a biomaterial. These results lead to increased knowledge of the role of carbon and nitrogen content in the behavior displayed by the different alloys studied.

Abstract

Corrosion products formed on the surface of two silver brazing alloys after the potentiostatic polarization in 3.5% sodium chloride solution were characterized by the standard methods such as, the X-ray diffraction, micro-Raman spectroscopy, and scanning electron microscopy with energy-dispersive spectroscopy. This paper presents the results of a laser desorption/ionization mass spectrometry (LDI MS) analysis as a new approach to the characterization of corrosion products. The potential of the anodic polarization was 0.5 V versus saturated calomel electrode, and the process duration was 300 s. The corrosion layers on both investigated alloys were similar in composition with cuprous chloride and silver chloride as the main components and had strong indications of cuprous oxide formation. The major difference between these two layers was the existence of zinc hydroxychloride as the corrosion product of Ag-Cu-Zn alloy. Palladium compounds were not found in the case of Ag-Cu-Pd alloy. The results of different methods have shown a good consistency. Complementarity between the used methods was useful in the interpretation of the results for each used method. This study has demonstrated that LDI MS can be used as an efficient additional method together with the traditional ones.

Abstract

The corrosion mechanism of copper and copper alloy is reviewed. A number of scientific papers have been investigated to determine the corrosion mechanism and protection techniques of copper and copper alloy corrosion. Results have shown that copper can be corroded in an acidic or an alkaline environment, and oxide formation is the corrosion initiation process. The use of corrosion inhibitors is one of several ways of controlling metal corrosion. There are inorganic (toxic) and organic (green) corrosion inhibitors invented so far. Nowadays, environmental issue is a concern of several scientists in the world. From the results of recent scientific papers, green corrosion inhibitors can be used for copper corrosion protection and they are both economical and environmentally safe. Furthermore, future researches are needed to determine more efficient, environmentally friendly corrosion inhibitors for copper and copper alloys.

Abstract

In order to advance material development for future nuclear systems, an insight into the cracking conditions of T91 ferritic-martensitic steel in heavy liquid metals (HLM) is provided. The paper critically reviews previous experimental data and summarizes them with new results. The new testing of T91 steel was performed in contact with slow flow and static HLM to study crack initiation, especially in liquid PbBi eutectic at 300°–350°C and Pb at 400°C with about 1 × 10−6 wt.% of oxygen. Pre-stressed coupons were exposed to the liquid metals for up to 2000 h. Constant extension rate tests (CERTs) were performed in the liquid metals to accelerate cracking development. Under static conditions, the testing resulted in oxidation without any crack observation. Under the CERT ones, the T91 steel showed a tendency to crack initiation in PbBi, while in Pb, cracks were not initiated even when the oxide layer was broken. Moreover, the environmentally assisted crack initiated at the maximum load and continued to grow under further loading without unstable failure. Both previous and new data have confirmed that high stress and plastic strain are pre-conditions for the environmentally assisted cracking of T91 in static HLM. It indicates that in the systems utilizing continuous oxygen control of HLM, the LME/EAC of the T91 could develop only in the beyond design load conditions. Further testing is necessary to address the HLM flow speed effect.