Papers by Keyword: Service Life

Abstract: This study presents a detailed analysis of the catastrophic failure of a Pelton turbine bucket, revealing a complex mechanism involving multiple interacting factors. Through a root cause analysis (RCA), the primary crack was identified to have originated in a high-stress concentration zone, exacerbated by pre-existing discontinuities. The turbine runner had accumulated approximately 90,000 service hours, suggesting a low-stress, high-cycle fatigue as the initial damage mechanism. However, the rapid crack propagation was driven by an abrupt shift in the fatigue regime, transitioning to high-stress, low-cycle fatigue induced by severe impact loads during counter-jet entry. This phenomenon led to the fracture of the bucket segment. This work emphasizes the importance of considering the synergistic interaction of accumulated fatigue, pre-existing discontinuities, and changes in the loading regime in the design and maintenance of Pelton turbines, to prevent premature failures and ensure the structural integrity of these critical components.

Abstract: The main objects of the EES, the service life of which exceeded the standard value, are increasingly beginning to determine the efficiency of work every year. This manifested in an increase in the number of automatic emergency shutdowns, the number and complexity of emergency-hazardous defects. Organization of operation, maintenance and repair of these facilities recommended carried out according to their technical condition. And since the technical condition determines the reliability and safety of the object, it is therefore recommended to take these properties into account more fully. These recommendations in the EES carried out at a high quality level, intuitively, according to operating experience.In this article, as distributed objects of continuous operation, overhead power transmission lines (OPTL) with a voltage of 110 kV and higher, the service life of which exceeds the standard value, are considered. The issues of quantifying the degree of significance of the aging problem for a set OPTL, their classification and methodology for assessing the difference in the degree of aging when classifying them according to given types of characteristics are considered. The methodology and algorithm of methodological support for the management of the EES and network enterprises during the organization of operation, maintenance and repair, been developed.

Abstract: The present research aimed to evaluate the effect of nickel-based electrochemical metallization (EMNi) on the quality and performance of electric motor components, compared to high-velocity oxy-fuel (HVOF) thermal spray coating, the most widely used coating in the mining industry. The experiment was conducted using motor components comprised of 4340 VCN steel, 4140 VCL steel, 1045 steel, and stainless steel, which underwent both treatments. The surface temperature of the components was monitored during the processing stage, followed by evaluations of their Rockwell hardness (HRC) and surface characteristics (taper, ovality, parallelism, finish, wear) at the onset (day 0) and after 2 years of use the results indicate that EMNi delivers electric motor components with superior finishes and extended warranty and service life in comparison to HVOF.

Abstract: The paper considers the issue of the influence of ambient temperature and service life on the endurance of pipe steels of underground pipelines. The results of numerous experimental studies allowed us to draw the following conclusions. An analysis of the experimental data indicates that for all the studied steels, the endurance decreases with decreasing air temperature, mainly down to-20... -30 °C. This can be explained by the embrittlement of the metal, i.e. a decrease in the plastic properties of the pipeline metal structure. In addition, it can be seen from the given data that low-alloy steels 48KhN, 09G2S, 10GS have the highest endurance. Weak endurance is mainly typical of grade 20 carbon steel. Experimental studies show that with an increase in the service life of pipes, their endurance decreases, and this tendency is inherent in all the studied steels. Studies of the endurance of pipe steels under complex stress states show that static torsional stresses close to the yield strength, when tested in the air, do not reduce fatigue life. Although the corrosive environment significantly reduces the cyclic strength of steel under shear stresses up to τ_cr=05τ_Y, the conditional limit of corrosion fatigue is not lower than when tested for corrosion fatigue under the action of only alternating stresses in a symmetrical cycle. It could be considered that the torsional stress in the pipeline system does not exceed 10 MPa. In that case, their influence on practical calculations on the endurance of pipes of underground pipeline systems can be neglected.

Abstract: The paper presents the results of research focused on the analysis of mold wear for high-pressure casting of aluminum alloys. The functional parts of the molds were taken out of operation. Molded parts for aluminum alloy casting molds and cores are made of tool chrome and chromium-molybdenum steels. In the die-casting process, the mold parts and cores are exposed to intense thermal, mechanical, and chemical loads. High melt flow rates of aluminum alloys (up to 120 m.s^-1), high pressures (up to 120 MPa) and high maximum surface temperatures of mold parts (up to 550 °C) lead to erosion, abrasion, corrosion, and thermal fatigue of molds. The thermal load of the foundry cores is even higher (up to 600 °C) because they are not connected to the mold cooling system. Thermal cyclic loading from 80 °C to 550 °C leads to high tensile stresses on the surface of the molded parts / cores and consequently to the formation and propagation of thermal cracks. Frequent contact of the surface of the mold part with the melt causes the formation of growths (die soldering) due to corrosion caused by molten metals and consequently shortens the life of the mold parts and cores. Light and electron microscopy was used for mold analysis. Every degrading change in the shape of molds and cores will also affect the quality and dimensions of the castings.

Abstract: The paper presents proposals for technical solutions based on the interest shown by transport companies in the country to reduce the cost of maintenance of means of transport by increasing the service life of metal components that, in traffic, are subject to a severe process of wear degradation. Specifically, the paper proposes solutions to solve these problems in the case of urban public transport by rail (tram). The results obtained by ISIM Timisoara (implemented at public transport companies in the country) in the field of reintroduction into operation of used metal components from trams are presented. It also presents new, innovative and efficient technical ideas and solutions, from the point of view of the cost / performance ratio and in compliance with the conditions for guaranteeing traffic safety. It is proposed to design and implement a flexible, complex and high-performance automated system for the reconditioning of tram wear components.The implementation of the proposed automated solutions will ensure: significantly increasing the service life of parts subject to wear, reducing the costs of loading with functional layers by increasing productivity, improving part quality due to automation of the loading process, use of constant process parameters, established, controllable during process. Innovative solutions are also proposed for: mobile automated inspection system for determining the degree of wear of tram wheel bandages; method of real-time monitoring of the welding loading process; technical solution to protect the rubber damping elements against overheating and degradation (the solution allows the tires to be reconditioned without removing them from the wheels).Accurate and efficient uses of automated systems, process programming units are specific approaches to the development and modernization of welding and reconditioning technologies by welding.

Abstract: Welding tools are a determining factor in obtaining welded joints with desired characteristics. The international community pays great attention to research aimed at establishing the optimal characteristics of friction stir welding (FSW) tools. With the development of the FSW welding process with its own contributions, ISIM Timisoara has developed complex research resulting in the conception and design of (innovative) FSW welding tool solutions. A very important factor especially when welding high hardness materials is the durability / lifespan of FSW welding tools. The paper presents general considerations regarding the qualities that FSW welding tools must meet in general, but also ISIM achievements in the field of design and operation of welding tools. Studies regarding operating behavior of welding tools made of sintered tungsten carbide P20S, in terms of service life (wear), both in the case of applying the classical FSW welding process and the method of friction stir welding in inert gas environment (FSW-IG), when joining steels with wide industrial use (304L stainless steel, respectively DD13 steel), are also presented. Concrete data is presented with values of the degree of wear of the tools in the unit of time, in their critical areas: tools made of X38CrMoV5 steel alloy used for welding aluminum alloys with different characteristics, respectively tools made of sintered tungsten carbide P20S used for welding S 235 JR + N steel and 304L stainless steels.

Abstract: Erosion of the metal of mining and metallurgical equipment due to the impact of solid particles is one of the forms of wear that can significantly limit the service life of a working machine or technological equipment, for example, a pipeline conveyor, loading and unloading bodies of mine workings and metallurgical machines. At present, this problem has been little studied and there is not enough information in the literature to form a systematic picture of impact erosion of equipment elements of mining and processing plants. The purpose of the research was to study the fatigue strength and corrosion-mechanical crack resistance of some structural elements of mining and metallurgical equipment with a long service life in chemically aggressive environments. Experimental tests for corrosion fatigue (long-term strength) were performed under bending load. The tests were performed on a bend with zero average voltage and a cycle frequency of 30 Hz. The tests were performed in salt solutions with a concentration of NaCl 5%. To compare the results, tests were sometimes performed in the air. The given data analysis shows that the long-term fatigue of the metal of mining and metallurgical equipment is significantly reduced when reaching 20 years of operation, especially in an aggressive environment containing chlorine ions, which causes severe corrosion damage to steel equipment. In addition, samples cut from metal with a long service life in mining and metallurgical conditions (more than 20 years) are characterized by low long-term strength. It has been found that fatigue resistance decreases with an increase in the number of cycles. Steel samples tested based on N = 10⁶ and especially on the basis of N = 10⁷ cycles have low resistance, which inevitably leads to breakdown with the subsequent destruction of equipment. It has been established that with an increase in the service life of the experimental mining and metallurgical equipment, the fracture toughness of the metal decreases significantly, which causes further failure and destruction of technological equipment.

Abstract: Prevention of rebar corrosion is achieved in the design and construction phases, by means of suitable mix design, casting and curing, and adequate cover depth; this approach have been introduced in international standards (EN 206) and design codes (Eurocode 2). Additional protection methods (cathodic protection, stainless steel or galvanised rebars, corrosion inhibitors, concrete coatings) can be used in very aggressive environment, especially in presence of chlorides, or when increased service life is required. In this work a simplified performance-based approach, based on Monte Carlo simulation, has been used to evaluate the service life (initiation time of corrosion) in chloride containing environments. The results confirmed that cathodic prevention and stainless steels are the most effective protection methods to guarantee a safe working condition in a severe environment. The use of pozzolanic or slag cement is confirmed as an effective way to slow chloride transport and by this way to increase the service life.

Abstract: When erecting monolithic reinforced concrete structures, the structure of concrete can differ significantly from the laboratory standard due to the complexity of providing favorable conditions for hardening, and therefore the compressive strength and especially the frost resistance of concrete may not meet the design requirements, which can negatively affect the reinforced concrete structure durability and require amplification, especially in earthquake-prone areas [1, 2]. Increasing the durability of reinforced concrete structures is possible by creating a rational stress field, for example, by prestressing, incl. variable along the length of the structure [3,4], but this technique is difficult to implement for monolithic reinforced concrete structures. It is possible to use effective materials or methods of manufacturing structures [5, 6]. But this is also mainly problematic for use in the construction of monolithic reinforced concrete structures. Generally accepted methods of calculating the reinforced concrete structures durability subjected to cyclic freezing-thawing during operation, incl. in a water-saturated state, do not exist. At the design stage, ensuring the durability of such reinforced concrete structures is mainly reduced to the reasonable assignment of requirements for concrete quality indicators, depending on the operating conditions, which is the focus of BC 28.13330.2017 (EN 206) and GOST 31384-2017 from the premise of ensuring durability of at least 50 years. In the above-mentioned norms of the Russian Federation, in fact, two approaches are presented to ensure the durability of reinforced concrete structures during cyclic freezing-thawing, incl. in a water-saturated state, namely: designing a concrete structure capable of working under such conditions by standardizing the values of cement consumption, W/C ratio, class of concrete in terms of compressive strength, amount of entrained air, or rationing of concrete grades in terms of frost resistance F₁ (first base method GOST 10060-2012 provides for freezing in air, saturation and thawing in water) or F₂ (second base method GOST 10060-2012 provides for freezing in air, saturation and thawing in 5% sodium chloride solution). The purpose of this work is to compare various approaches to ensuring the durability of reinforced concrete structures operated during cyclic freezing-thawing and to analyze the provision of durability with standardized indicators when designing the structure of concrete.