To ensure the reliable functioning of the main pipeline for water transport in hydropower, which has been operational for 50 years, a detailed analysis of the pipeline’s material condition is ...necessary. The pipeline material undergoes changing exploitation and working conditions, including extreme load phases such as periodic intensive emptying and filling with water for inspection. In this paper, we analyse the material resistance of NIOVAL47 steel using the method for determining R-curves for three states: Normalised state (2 samples), aged state (1 sample) which underwent 10% cold deformation and was heated for 30 min at +250 °C, and deformed state (1 sample) which underwent 10% cold deformation. The test results indicate that analysing the material’s aged and deformed states is crucial for obtaining a reliable picture of the structural integrity of the NO2500 mm pipeline, which has been in operation for five decades. The study should demonstrate the current state and level of reliability of the pipeline in order to ensure the sustainability of the energy facility. Additionally, these tests provide a realistic picture of the necessity of introducing an online monitoring system for the pipeline.
In this paper, we will present our investigation of the quality of J55 microalloyed steel welds that were formed by a basic flux-cored wire electrodes that were of appropriate quality and alloyed ...with Ni and Mo. Based on the comparison and analysis of the obtained results related to the testing of the chemical composition, mechanical properties, toughness at test temperatures, and the microstructure of welding joints formed by a classic and specially coated rutile flux-cored electrode, we assessed the justification to switch from solid wire electrodes to flux-cored alloyed wire electrodes of appropriate quality. The research aim for the application of flux-cored wire electrodes instead of solid wire electrodes is based on the advantages pertaining to a flux-cored wire: molten metal from electrode wire is transferred in the form of fine droplets, easy welding and maximum productivity within all spatial positions related to welding, improved properties of welding joints, and increased productivity when compared to a classic solid wire. Our research encompasses the development of the experimental production at the Research and Development Center IHIS Belgrade (Development Institute for Chemical Power Sources), Serbia, of the new type of a coated electrode with improved welding properties when compared to a classic electrode intended for microalloyed steel welding.
In this paper we will describe the process of the deposition of thick layers of VPS-Ti coating, which is used as a bonding layer for the upper porous Ti coatings on implant substrates. In order to ...deposit the powder, we used HÖGANÄS Ti powder labelled as AMPERIT 154.086 -63 µm. In order to test the mechanical properties and microstructure of the VPS-Ti coating, the powder was deposited on Č.4171 (X15Cr13 EN10027) steel substrates. Mechanical tests of the microhardness of the coating were performed by the Vickers hardness test method (HV0.3) and tensile strength by measuring the force per unit area (MPa). The microhardness of the coating is 159 HV0.3, which is consistent with the microstructure. The coating was found to have a good bond strength of 68 MPa. The morphology of the powder particles was examined on a scanning electron microscope. The microstructure of the coating, both when deposited and etched, was examined with an optical microscope and a scanning electron microscope. By etching the coating layers, it was found that the structure is homogeneous and that it consists of a mixture of low-temperature and high-temperature titanium phases (α-Ti + β-Ti). Our tests have shown that the deposited layers of Ti coating can be used as a bonding layer for porous Ti coatings in the production of implants.
This paper deals with analysis and comparison of the equivalent plastic strain and temperature fields in the aluminium alloy 2024 T3 (AA2024 T3) joint, with macro/microstructure appearance and ...hardness profile. In the alloys hardened by heat treatment, grain size and particle size of the precipitate are functions of equivalent plastic strain, strain rate and temperature. By analysing the equivalent plastic strain fields and temperature fields it is possible, to some extent, to capture the effect of welding parameters and thermo-mechanical conditions on grain structure, and therefore hardness and strength in the welded joint. A coupled thermo-mechanical model is applied to study the material behaviour during the linear welding stage of friction stir welding. The 3-D finite element model has been created in ABAQUS/EXPLICIT software using the Johnson-Cook material law. The values of thermo-mechanical quantities during the welding stage are obtained from the numerical model and shown as distributions across the joint. The obtained values of these quantities are related to the microstructure of the joint zones and hardness distribution, and this relation is discussed.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The paper provides an assessment of the integrity and remaining life of the structure, i.e. an assessment of the remaining life of the pressure vessel from the aspect of exploitation conditions. The ...obtained results and analysis of the results should give a practical contribution to the assessment of the influence of exploitation conditions on the behaviour of the base material, components of the welded joint and the pressure vessel, intended for a work on higher temperatures, all with the aim of assessing the integrity and remaining life of the structure, as well as revitalization and extension service life of process equipment made of steel for working at higher temperatures.
This paper describes pipeline stress analysis, primarilybranch junctions, as a structural element in hydro-power plants. Pipelines are exposed to internal pressure,which is present under working ...conditions. Analysis of stresses in the pipeline of the hydropower plant is based on analytical, numerical, and experimental methods. In this paper, we will define the critical elements of the pipeline. After that, we will determine critical areas in the branch junction, under experimental conditions, where strain gauges should be installed. The obtained results show that a boiler formula can be efficiently applied in the stress analysis. Also, a correlation between the internal pressure and the maximum circumferential stresses in the elastic zone is given. In the final sections of the paper, the limit value of the internal pressure as a load for which stress in the zone of plasticity appears and the safety factor of the branch junction in the exploitation conditions are determined. The contribution of this work is the unification and deepening of the topic related to the problem of the testing of hydro-power structural elements. Keywords:pipeline, branch junction, hydropower plant, strength analysis, shell intersection
The influence of friction stir welding parameters on thermo-mechanical behavior of the material during welding is analyzed. An aluminum alloy is considered (Al 2024 T351), and different rotating and ...welding speeds are applied. The finite element model consists of the working plate (Al alloy), backing plate and welding tool. The influence of the welding conditions on material behavior is taken into account the application of the Johnson-Cook material model. The rotation speed of the tool affects the results. If increased, it contributes to an increase of friction-generated heat intensity. The other component of the generated heat, which stems from the plastic deformation of the material, is negligibly changed. When the welding speed, i.e. tool translation speed, is increased, the intensity of friction-generated heat decreases, while the heat generation due to plastic deforming is becoming more pronounced. Summed, this leads to rather small change of the total generation. The changes of the heat generation influence both the temperature field and reaction force. Also, the inadequate selection of welding parameters resulted in occurrence of the defects (pores) in the model.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Without the increase in welding current, activating fluxes for arc welding with a non-consumable electrode (ATIG) and for welding with a consumable electrode (AMIG) allow for the increase in depth of ...penetration 2-4 times. These two procedures are essentially different in terms of their implementation. In AMIG welding, the problems in the creation of a welding joint stem from the influence of the critical value of the metal bath surface. The critical value of the surface is achieved by using welding current of 280-300 A and, according to the experimental results, its value is 160-190 mm². By achieving the critical surface value, the positive influence of the activating fluxes on the penetration ability of the electric arc is lost. Optimum interval of welding current for AMIG is 200-500 A, which significantly exceeds the permissible threshold. In ATIG welding, the effect of the critical surface of the bath is not observed, because it requires welding current that exceeds the optimal value interval (max. 250 A), which is conditioned by the stability of the non-consumable electrode. By increasing welding current over 250-300 A, the working tip of the electrode is rapidly consumed and the stability of the welding process is disturbed.
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