Abstract: In the paper there are presented experimental results concerning mechanical characteristics of friction-welded joints in comparison with electron beam welded joints, made by 20VNiMoCr120 heat-resistant steel, which are part of some elements working at high pressure and temperature. The paper represents a study which suggests non-conventional welding and heat-treatment procedures for water and steam-supply pipes, large cylindrical recipients with high values of wall thickness, boiler pipes, steam turbines which compose thermo-energetic installations, in order to prevent failure appearance. The actual level of development in all activity fields proves the fact that on top of the performance and modernism, technological products and processes must assure a high reliability. All the results and experimental researches are obtained by the first author in her PhD Thesis.
Abstract: Catalytic properties of the solid component of welding aerosol (SCWA) of different origin, both in powder form and incorporated in synthetic fibrous materials, in the reaction of ozone decomposition have been studied. For powder samples, the protective time as well as the amount of the decomposed ozone decrease in the order SCWA-ANO > SCWA-UONI > SCWA-TsSL due to the decrease in the content of magnetite and manganochromite phases. Catalytic activity of the SCWAs increases after their incorporation into the fibrous materials.
Abstract: Vertical Kaplan turbines, manufactured in Russia and with nominal power of 200 MW, have been installed in 6 hydroelectric generating units at hydro power plant Djerdap 1. Hydroelectric generating sets have been designed for the service life of 40 years due to structural solutions and limited possibilities of performing periodic inspections and state analyses.During the rehabilitation of the hydroelectric generating sets, non-destructive tests were performed on all components and structures in order to complete state analysis. In this paper the damages and methodology of repair welding for damaged glasses, which are the integral part of the kinematic system of runner blades, are presented.
Abstract: The paper presents test results of a new quality of a special rutile electrode, with a core of flux-cored wire made from local raw materials, based on analyzing mechanical properties and microstructure of the weld metal in MMA welding. The base metal for experimental welding was microalloyed steel marked J55 (thickness 7.0 mm) according to API Spec 5L standards (EN 10113-3. and JUS C.B0 502) which was produced in Smederevo steelworks. For experimental welding a special electrode IHIS E 35 R-2 was used, with a medium thickness rutile coating, a core of flux-cored wire and Ni content of 2.5%. The results of the analyzes indicate that the new quality special rutile electrode with the flux-cored wire core provides good structural and mechanical properties of weld metal in microalloyed steel welded joints.
Abstract: For the examination of noxious emissions, cladding tests were performed according to EN ISO 6847. The filler materials were 1.2 mm diameter wire-electrodes, made of tin bronze, aluminium bronze, austenitic stainless steel, duplex stainless steel and nickel alloy.The low-energy metal transfer welding process, named CMT (cold metal transfer) was examined, on the welding source type Trans Puls Synergic 2700 CMT, of 270 A, produced by the company Fronius, Austria. For sampling welding smoke particles, an Apex type pump was used. For measuring the concentration of gases emitted by welding, a Triple Plus type multi-gas detector was applied.The particulate emission rate is 0.500 mg / m3 in the breathing zone, according to ISO 10882-1. For comparison, the measured emission rate is from 0.877 to 2.513 mg / m3 in the welding zone, according to ISO 15011-1. The concentration of the emitted gases is in the ranges: 0.14 to 0.16% CO2; 0.1-0.2 ppm NO2; 0-15 ppm H2; 0-5 ppm CO. These concentration levels are below the exposure limits (8 hours per day, five days a week): 5% CO2; 1.0 ppm NO2; 30 ppm CO. In conclusion, the emissions from the CMT welding process are without health risk for the welder.
Abstract: The reactions of the base material, during the welding process, consist in chemical composition, volume, structure and granulation changes. There are multiple problems which can occur by welding two steels with totally different chemical composition, i.e. carbon steel S235JR + AR and austenitic stainless X2CrNiMo17-12-2. The process used for making the heterogeneous joint was flux cored arc welding (FCAW), numerically coded 136. The paper presents the effects of welding through heat input, on the structural characterization of welded seam and heat affected zone. It also focuses on the structural characterization of the welded joint obtained using the flux cored wire T 23 12 L P C/M 1, and determining how the base materials participate at the formation of the welding joint.
Abstract: Nuclear experimental instrumentation frequently includes the usage of thin-walled (metallic sheathed) thermocouples passing through the boundaries of pressure vessels. This is accomplished by sealing the thermocouples by brazing through special design fittings (passages) which are later sealed / welded to the body of the vessel.Two are the challenges to face : (a) the manufacture of the instrumented passage (b) its mandatory qualification, according to relevant standards. Even the brazing qualification standards are more flexible than for welding, the peculiar situation of nuclear instrumentation still needs special consideration and it is not properly covered by the regular standards.The paper describes the experience of the authors in manufacture of the instrumented passages with steel or Inconel sheathed thermocouples, along with some other known projects, in conjunction with applicability of relevant standards: ASME code, AWS standards, national standards. Since it is about pressure vessels, ASME prescriptions are mandatory in Romania; other standards may serve as valuable sources for the “engineering judgment” allowed and recommended by ASME code.The main problem in such specialty brazing qualification is that for some combinations of base metals and filler (imposed by application), one cannot avoid the significant fragilization due to a tremendous increase of hardness in the brazing area. Base material erosion is added and the effect is catastrophic : sectioning the thermocouples at the slightest movement. For example, brazing Inconel thin-walled tubes with BNi-7 is very hard to control – experimental data and images are included in the paper to illustrate this.Therefore, special means must be applied both in fabrication and in qualification, in order to ensure the product is functional and safe, even being fragile. This approach can be found in French design of irradiation devices, being also considered in the French code for design and construction of experimental reactors and irradiation devices. Being known that French experience in this field is vast, their approach makes us confident that our brazing technique is not wrong but the problem is to be solved through ‘smart’ design and specific procedures. Consequently a tentative set of domestic rules for work and qualification is proposed for discussion and further improvement.
Abstract: In this paper spot-welding technology of sheets made of Dual-Phase (DP) steel, which is one of the most important materials in the automotive industry, has been analyzed using finite element modelling and experimental research. The traditional, continuous energy input and the symmetric double pulse as non-continuous energy input were compared for resistance spot welding focusing on the advantages of pulsed energy input. For numerical analysis an axisymmetric coupled finite element model was developed to study the effect of welding time and current intensity on nugget size and thermal history in resistance spot welding process using MSC.Marc software package. The cross-section macrostructures of the welded specimens were examined and compared to the predicted size of the weld nugget and heat affected zone.
Abstract: Welding as a modern, highly efficient production technology found its position in almost all industries. At the same time the demands on the quality of the welded joints have been constantly growing in all production areas. Great demand on the quality of the welded joints consequently causes more experimental or prototype – so called – validation joints that take place before the welding of final construction. These experiments, prototypes aim at – for instance – defining the appropriate welding technology, material, pre-heating, welding parameters, clamping condition and optimizing the welding process. Naturally, these experiments and prototypes make production more expensive. Numerical simulations of welding – in the area of production preparation as well as of production proper – have been frequently used recently. Numerical simulations supported by experimental measurements can simulate the actual welding process very close to reality. The new material models for hardness and mechanical properties prediction based on numerical simulation solution will be introduced.The paper covers some typical welding cases from energy industrial sector. The homogenous and heterogeneous weld joints from modern energy Cr-Mo-Ni-V steels (including modern austenitic steels) were done as prototype welding. The numerical simulation of these weld joints including post weld heat treatment process were done and welding technologies were optimised based on the numerical simulation results. The calculated hardness was compared with real measurements. During project the complete material properties which are needed for numerical simulation were measured. Simplify numerical lifetime prediction of weld joints including results from numerical welding analyse (as residual stresses and plastic deformation) were done.