Papers by Keyword: Pitting

Abstract: It is known that heat treatment (HT) highly affects the properties of base metal (BM) and fusion zones (FZ) of duplex stainless steel (DSS). In fact, it may give unwanted structure changes. Duplex stainless steels SAF 2205 welded joint was subjected to thermal cycle at temperature of 850^◦C at holding times 1, 3, 5 and 7 hours. The influence of heating cycles and concentration of corrosive medium on the corrosion properties and microstructure of 2205 alloy was the objective of this work. It was found that process led to noticeable decrease in the corrosion resistance of BM and FZ specimens; moreover the decrease was large in BM than FZ. It was also found that sigma phase (σ) precipitated in the different zones of the structure. σ phase volume fraction was found to increase with increasing the holding time of HT, and its increase is larger in BM. Corrosion resistance was found to be oppositely related to σ phase formation. Secondary austenite phase (γ₂) was also precipitated and its volume fraction in FZ was found to increase with increasing the holding time of HT and decreased in BM.

Abstract: The present work investigates a hybrid nano-coating based on permanganate/fluoride/glycerol conversion coating solution on aluminium alloy, AA6061. From gravimetric studies, the nano-coatings formed on aluminium alloy by immersion procedures developed rapidly at a rate which decreased with time of treatment and was about 5 gm^-2 after a period of three minutes. The morphology of the coating from scanning electron microscopic (SEM) examinations revealed randomly shaped coating materials with mud cracking patterns, characteristics of dried out coatings derived from gel-like materials. Analyses of the coating with the energy dispersive analysis of X-ray spectroscopy (EDS) attachment in the SEM revealed the composition as compounds of aluminium, oxygen and manganese, probably hydrated. The corrosion resistance of the coating out-performed ‘bare’ aluminium alloy specimens exposed to both natural and 3.5% sodium chloride solution environments. The coating improved the paint adhesion characteristics of the substrate aluminium alloy. Macro and micro features developed on the substrate aluminium are anchor points which improved the adhesion of subsequently applied lacquer.

Abstract: The corrosion behavior of Al-B₄C metal matrix composites in H₃BO₃ solutions with different Cl^- contents was investigated using potentiodynamic polarization and zero resistance ammetry techniques. Results show that the corrosion of Al-B₄C composites in H₃BO₃ solution increases with increasing B₄C volume fraction in the composites. The main corrosion characteristic of Al-B₄C composites in H₃BO₃ solution is the galvanic corrosion between Al matrix and B₄C particles. In the galvanic couple, B₄C particle acts as cathode and Al matrix acts as anode. The cathodic reaction is hydrogen revolution reaction, which controls the corrosion mechanism of Al-B₄C composites. Pitting is not observed on the composite surface in the H₃BO₃ solution with zero Cl^-. However, with addition of Cl^- in H₃BO₃ solution, pitting occurs and the corrosion resistance remarkably decreases with increasing Cl^- content. The corrosion resistance of Al-B₄C composites in H₃BO₃ solutions is compared with that in the standard 3.5% NaCl solution.

Abstract: The pitting corrosion behavior of AISI 202 stainless steel (SS) – a low-nickel, austenitic SS grade, was investigated by means of cyclic voltammetry (CV) technique complemented by Scanning Electron Microscopy (SEM). From the starting potential, the current density decreases and changes its sign at the corrosion potential (Ecorr). The anodic response exhibits a well-defined anodic peak followed by a passive region. A noticeable increase in the anodic current density was observed after reaching the breakdown potential (Eb). The second anodic peak which may be attributed to onset of oxygen evolution was also observed. Moreover, the cyclic voltammograms revealed that hysteresis loop is absent for all the studied concentrations, indicating that AISI 202 SS in citric acid is highly resistant to pitting corrosion as also supported by the results of SEM. It was found out that the critical current density (icrit) increases with increasing citric acid concentration.

Abstract: The paper deals with a problem of stress crack initialization on surface of low pressure steam turbine blade during operational regime. The mention stress analysis together with described environment indicate procedure of experimental works. The other goals of research should lead to a concept of assessment methodology of resistance of moving blades against corrosion and technology increasing fatigue strength of blade steels using surface strengthening. A prototype of the moving blade of the low pressure stages of steam turbine with the increased corrosion resistance should be an output of developed efforts.

Abstract: Literature reported extensive work on the failure of Industrial power transmission systems, during their routine torque transmission, rotary motion etc. During transmission through gear drive the noise, temperature, stresses, vibration etc are important factors to be considered. When one or more of above exceed certain design limits, the drive and its accessories must be examined for the cause and a preventive maintenance is to be followed. The latest research work carried out, in above area is reviewed. The cause of failure and failure analysis is examined. An attempt is made in this paper, to systematically analyze the modes of failures, the reasons for the same, issues and challenges involved, there in, and measures to be taken for addressing them. This analysis is likely to help the researchers to proceed further in analyzing the failure and to suggest means to prevent failure of gear power transmission systems. The major contribution of present work is, to present the common modes of failure of gear teeth in power transmission systems, and measures to be taken to address the same. In general various additives in the lubricating oil help in controlling initiation of pitting. The present work involves controlling one of the additives namely sulphur in the lubricating oil to control pitting. The present work forms an excellent basis for identifying various other parameters affecting the pitting failure of gear teeth in a gear box.

Abstract: The dismantled tubes of the steam-boiler operated by the “Kalush Heat and Power Plant” were investigated. Defects of various nature, pitting of the indefinite shape were found during the examination. Since pitting is a deepening in the material and contains dark products of the corrosion process. It looks like a darkened area that stands out against the light background of the non-damaged surface in the optical images. The efficiency of such processing for identification of the corrosion defects is analyzed. The suitability of the proposed methods for the calculation of Shannon entropy of the surface analyzed was tested, as well as for determining the area and number of pitting defects.

Abstract: Type 303 austenitic stainless steel has been applied in jewelry production, and its nickel release rate has become a concerned issue in the jewelry industry. In this paper, the commercial type 303 stainless steel was used as the test material, while 304 stainless steel as the contrast material; their nickel release rates and corrosion behaviors in artificial sweat were studied. The results show that the actually measured nickel release rate of 303 stainless steel reaches 2.06μg/cm²/week, nearly 25 times higher than that of 304 stainless steel, which exceeds the threshold specified in nickel release standard EN1811:2011 for jewelries coming into direct and prolonged contact with the skin (0.88μg/cm²/week), and its adjusted value also exceeds the threshold specified in Nickel Directive 2004/96/EC for puncture accessories (0.35μg/cm²/week). The high nickel release rate for 303 stainless steel is mainly caused by its high sulfur content and the inevitable formation of manganese sulfide inclusions, which will cause the pitting and exacerbate the material corrosion. Considering the risk of nickel sensitization of 303 stainless steel, it is not suggested to use 303 stainless steel as the jewelry material, especially for piercing jewelry.

Abstract: The pitting behavior of 304 stainless steel in the simulated condensate with different salt content (4 mg/L, 8 mg/L, 16 mg/L, 32 mg/L, 64 mg/L) and sulfur content (1.2 g/L, 2.5 g/L, 5 g/L) was studied using potentiodynamic polarization curve and static immersion methods. The simulated condensate was simulating the condensed water in the unit of refining heavy oil with high salt and high sulfur. The results showed that with the increase in chloride ions concentration, the pitting potential of 304 stainless steel decreased and the pitting sensitivity increased. The pitting sensitivity of 304 stainless steel also increased with the increase in sulfide ions concentration. In several experimental mediums, when the concentration of chloride ions and sulfide ions were 64 mg/L, 5 g/L respectively, the number and the size of corrosion pits both were the largest, the pitting behavior was the most serious.

Abstract: Gear is one of the most important and commonly used components in machine system. Early detection of gear damage is crucial to prevent the machine system from malfunction. This paper proposes a method for detection of damaged tooth based on support vector machines. Statistical parameters of standard deviation, root mean square value, maximum value and mean value are extracted from the vibration signal as representative features of tooth conditions to be input to the support vector machine classifier. The validity of the presented method is confirmed by the application of detecting early damaged tooth during the cyclic fatigue test. The vibration acceleration on gear box is acquired as original data. Furthermore, the signal of each gear tooth is separately extracted from the signal for a further analysis.The experimental results demonstrate the effectiveness of the proposed method.