Papers by Keyword: Weld Joint

Abstract: The aim of the work was to assess the nature and causes of defects – cracks in the welds of membrane wall panel tubes (MW) of a thermal power plant boiler made of T24 steel. This steel is intended to produce MW evaporators and superheaters for power plant units operating in the area of supercritical steam conditions. Its advantage, compared to the originally used materials, is higher creep resistance. The main expected advantage of the steel was to obtain optimal properties of welded joints without subsequent post-weld heat treatment (PWHT).

Abstract: The aim of the work was to find out the causes of cracking of the A120 crane track rail. Although the track was regularly inspected by defectoscopic techniques, after five years of operation, the rail was broken at the weldment. The elemental composition of the welded joint materials was verified and the mechanical properties were determined. A fractographic description of the fracture surface was performed and the structure of the material was evaluated. Several factors contributed to the formation of crack, the combination of which led to a rail failure. Defects of the welded joint, acting as notches, from which they initiated fatigue cracks, unfavourable microstructure of the weld metal, low toughness of the base material and operating environment and conditions were dominant.

Abstract: Residual welding stresses affect significantly the strength, durability, and performance of structures. Therefore, there is an urgent need for developing and implementing techniques and equipment that allow reliably estimating stresses in experiments. This paper considers some aspects of the joint implementation of electronic speckle pattern interferometry and the spot drilling technique to determine these characteristics under the field conditions. The results of determining the distribution of residual stresses in the weld joint areas of DN 850 pipes are given for various welding modes. The study results are of independent significance and herewith, demonstrate the efficiency of the equipment developed to solve similar problems.

Abstract: The crack propagation of different weld joint samples were detected by acoustic emission (AE) technique. The samples were from the basic metal, weld seam and heat affected zone (HAZ), The results showed that the crack growth rate of basic metal was higher than weld seam and HAZ because of the transverse compressive residual stress in joint. But the coarse of grains was the reason for higher rate of weld seam than that of HAZ. And AE waveforms of crack propagation from three microstructures were different. The most compositions of AE signals were higher frequency of 300KHz for weld seam and lower one of 100KHz for basic metal and HAZ.

Abstract: The problematic of welding in terms of weld quality in dependence on service life of mechanical structures is discussed. Some examples of inadequate quality weld joints causing failure under load are described. Materials of the evaluated welds were following: S355 steel and Inconel 635 super alloy. Service conditions of homogeneous welds were different for both materials and weld quality was covered by Welding Procedure Specification. Using metallographic evaluation, the main problems were detected in a form of geometrical imperfections or insufficient penetration. These existing imperfections combined with static and dynamic load initiate the partial malfunction or failure of parts or constructions.

Abstract: Welding technology at current level provides wide range of applications such as automotive or aerospace industries. New technique, ways of approach and use of new materials (for example aluminum or composite parts of car body parts) creates necessity of optimizing of welding.The article is focused on welding of two parts using Metal Active Gas (MAG) welding. The main task is to design most suitable parameters for welding structural steel S235 J0. Samples were prepared by CNC machining center by chamfering edges 30°. Machined samples were placed against each other creating angle of total 60°. Welding machine Einhell BT-GW 170 MAG was used to create V and Y shaped welds with various technological parameters. Goal of the article is experimentally determine combination of technological parameters for V and Y shaped weld joints of steel components with thickness of 6 mm focused on hardness. Every welding machine and of course additive material has some recommended values of parameters in large scale, therefore it is necessary to determine most appropriate combination of main welding parameters. Data obtained from experiment showed most suitable combination of variables of welding process in order to achieve highest quality of weld joint.

Abstract: This paper applied the micro-arc oxidation technology to TIG weld joint based on titanium alloy. The optical microscope, SEM, XRD and polarization curve were used to analyze the joints metallographic phase, the coating morphology, the phase composition and corrosion resistance. Research results showed that the grain was grew gradually coarser from base metal to joint. The joint surface obtained a uniform morphology after micro-arc oxidation. The joint and base metal was made up of α-Ti and their coatings are mainly composed by rutile-TiO₂. The surface morphology and phase composition are similar after micro-arc oxidation. Polarization curve tests demonstrated that the corrosion potential performance of the coating was enhanced by micro-arc oxidation.

Abstract: Development of new steels with higher creep resistance must be based on detailed knowledge of strengthening and degradation processes, structural stability at high temperature exposure and their welding. This paper is concerned with the real weld joint hardness and microstructure of progressive low alloy creep resistance T24 steel. These steel is widely used in many power-plant constructions all over the Europe. Welding the T24 steels components is one of the most important technological procedures. The aim of the performed investigation is to evaluate the hardness and microstructure in the heat affected zone (HAZ) and the weld metal. Results of the secondary hardening in the real weld joints after low temperature post weld heat treatment (460°C/48h) and without post weld heat treatment at service temperature are described in this paper. Obtained results are compared to the hardness values of the weld joint post weld heat treated at recommended temperature (740°C). The microstructure of the real weld joints was analysed by transmission electron microscopy (TEM) in order to identify minority phases - MX nanoparticles and/or coarse (M₂₃C₆) particles. Secondary hardening of the not heat treated and low temperature heat treated T24 weld joint was proved.

Abstract: The use of new construction materials is increasingly on demand for the construction of new power plants, and for the modernization of existing plants that are at the end of their service life span. Steels such as type P/T92 (modified martensitic 9-12% Cr), and low-alloy steels derived from modified steel 2.5Cr1Mo (ASTM marked P/T23) are considered promising alternatives. In the construction of power units, the so-called heterogeneous joints, which most often consist of a combination of low-alloyed materials and highly-alloyed ones, preferably need to be avoided. These welded joints are often the weak links in the overall construction. Knowledge of the behaviour of creep-resistant steel welded joints is very important for the subsequent evaluation of the life span of the units. This study deals with the degradation of heterogeneous welded joints of steel T23 - T92 and 15CH1M1F - P91, using the commercially available welding materials Thermanit MTS 616 (highly-alloyed), Union I P23; ThermanitP23, Böhler P23-IG and Thermanit (FOX) P23 (low-alloyed). In the heterogeneous welds examined, slight loss of strength of the base material was observed during isothermal heat exposure and extension of the diffusion active zones (i.e., Carbon Depleted Zone (CDZ) and Carbon Enriched Zone (CEZ)). These degradation processes caused structural instability of heterogeneous welds. It was found that the use of low-alloyed welding materials showed superior structural stability than highly-alloyed welds. Additional laboratory analyses are warranted due to the extreme service conditions and the high temperature loads in power units.

Abstract: An ultrasonic method was developed to measure the residual stress in a welded joint based on the modified acoustic-elasticity theory. Phase frequency analysis method was introduced by incombination with shear wave and longitudinal wave. The acoustic-elasticity parameters of joint material was derived by ultrasonic inspection during loading experiment. Transverse and longitudinal residual stress was determined by precisely measuring of short-distance acoustic travel time. The ultrasonic measurement results was confirmed by H&K theory and XRD methods with good repeatability and reliability.