In this paper, numerical investigation was systematically performed using thermal elastic-plastic analysis to study the effect of welding conditions in embedded flaw repair technique, such as weld ...heat input, crack depth and thickness of structural member, on the welding-induced residual stress at repair welds of nuclear power plants. The stress intensity factor (SIF) was also estimated based on the calculated distribution of residual stress around the remaining crack within repair parts. Meanwhile, the essential variable of welding conditions described above was theoretically derived from welding thermal conduction theory as representative of the temperature distribution along the crack to conduct the unified evaluation on the relation between the residual stress and the SIF around the remaining crack and welding conditions. As the results, it was concluded that the residual stress and the SIF at the downside crack tip region could be arranged by a unified curve associated with the essential variable derived. Besides, the residual stress becomes compressive and the SIF becomes zero when the essential variable is smaller than approximately 1.5. Further investigation was numerically performed for multi-layer and multi-pass repair welding process to study the effect of weld pass sequence on the residual stress and the SIF around the remaining crack. Then, it was clarified that the appropriate weld pass sequence condition was dependent on value of the essential variable described above. With the right selection of weld pass sequence, the residual stress and the SIF after multi-layer and multi-pass repair welding is possible to be compressive and zero respectively even when the essential variable is vastly larger than approximately 1.5 to introduce the highly tensile stress at the downside crack tip region after single-pass repair welding. Thus, the methodology to improve structural soundness for preventive maintenance at repair welds of nuclear power plants was developed on the basis of the essential variables of welding heat input and pass sequence conditions in embedded flaw repair technique.
A change in linear welding conditions, namely higher vibration frequency (150 Hz) and lower displacement (2 mm) during welding, produced a quicker rise in temperature of the weldline. This allowed a ...much shorter welding time (1.5 s). X-ray microdensitometry mapping showed a progressive
increase in broadening and average density of the weldline as the welding time lengthens. As the welding time lengthens the maximum temperature reached at the end of welding is progressively higher. This causes increasingly greater degradation. This effect was confirmed also by CP-MAS
13
C
NMR and it was found that the lower is the degree of deterioration of the weldline of the wood joint the shorter is the welding time. Monitoring of the temperature of the weldline showed that the temperature reached in wood joints during welding was inversely correlated to its water resistance.
Furthermore, the increase in weldline temperature is markedly quicker at a vibration frequency of 150 Hz than at 100 Hz. Thus, the shorter is the welding time the lower is the degree of deterioration of the weldline of the wood joint. This appears to be due to welding occuring when water vapour
is still present in the joint, hence providing a less damaging welding environment.
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BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
A change in linear welding conditions from those previously used, namely higher vibration frequency (150 Hz) and lower displacement (2 mm) during welding afforded a quicker rise in temperature of the ...weldline. This allowed a much shorter welding time (1.5 s). This resulted (a) in no
fibres being expelled from the welded interface edge and (b) the thin exposed interface seen on the joint side not being dark, indicating almost no charring of the interfacial region. The maintenance of all the fibres in the interfacial composite ensured a stronger joint and a much improved
water resistance due to the decrease and almost absence of the rather porous weldline char which would have facilitated water penetration. Such change in the set of parameters allowed resistance of the linear welded joints in water for more than 25 h.
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The effectiveness of welding with a trailing heat sink in reducing the angular distortion of a weld has been experimentally investigated with focus on the cooling position. A numerical model of ...welding with a trailing heat sink is constructed through the comparison of measured values of weld penetration, thermal cycles and angular distortion with those calculated. On the basis of this model, the effect of welding heat input conditions on the reduction in angular distortion is discussed to evaluate the versatility of welding with a trailing heat sink. The results indicate that the choice of an appropriate cooling position behind the welding heat source is essential for the effective reduction in angular distortion. The reduction in angular distortion by the heat sink at the appropriate cooling position increases with the heat input parameter Q
net
/h
2
, where Q
net
is the weld heat input and h is the thickness of the plate.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
In this paper, dominant factors influencing the weld angular distortion were discussed on the theoretical basis of the relation between weld angular distortion and distribution of inherent strain for ...the more accurate quantifying and managing the weld angular distortion. Based on the experimentally observed relation between highest temperature and inherent strain distributions, the mechanical melting zone was focused as the temperature distribution corresponding the generation area of inherent strain controlling the weld angular distortion. TIG bead-on-plate welding of high tensile strength structural steel was performed under the various welding conditions to investigate the effect of welding conditions on the weld angular distortion. And then the weld angular distortion was arranged by the conventional parameters of weld penetration and weld heat input, and the newly proposed parameter of the mechanical melting zone. As the results, it was confirmed that the weld angular distortion could be arranged more coordinately by the proposed parameter of mechanical melting zone rather than the conventional parameters of weld penetration and weld heat input. Thus, it was concluded that the mechanical melting zone should be focused as temperature distribution controlling the weld angular distortion for the more accurate quantifying and managing the weld angular distortion.
We investigate, how welding conditions affect the arc in TIG welding with a constricted nozzle by numerical simulation using an axial-symmetric two-dimensional model. When helium is used as a ...shielding gas, the effect of the constricted nozzle is more remarkable than argon. The heat flux to the centre of the anode surface increases more with a higher welding current. This feature is suitable for pulsed welding. Even if an electrode is consumed and its tip angle is changed, a stable arc plasma and heat intensity are obtained.
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This study concentrates on the effects of weld sequence and welding fixtures on distribution and magnitude of induced arc welding residual stresses built up in butt-joint of Gas Tungsten Arc Welding ...(GTAW) AA5251 plates. Aluminum plates have been welded under different welding conditions and then, longitudinal and transverse residual stresses were measured in different points of the welded plates employing hole-drilling technique. The results indicate that welding sequence significantly alters the distributions of both longitudinal and transverse residual stresses while the changing in the weld sequence leads to 44% decrease in longitudinal residual stress. Besides, both the geometry of weld pool and distribution of residual stresses are affected by the welding fixtures while implementation of fixture causes about 21 and 76% reductions in the depth of weld pool and transverse residual stress, respectively, for the material and welding conditions used in this research.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In recent years, in-process control welding for reducing weld distortion and residual stress is much more required from a view point of improving manufacturing efficiency. In-process control welding ...by additional cooling has been proposed as one of techniques for reducing weld distortion and residual stress. It has already been partially applied for thin-plate structure in industry. In order to extend the range of application of in-process control welding by additional cooling in the future, further studies are required. Firstly in this study, reduction of angular distortion by heat-sink welding is experimentally discussed. Based on the experimental results, effect of welding conditions on reduction of angular distortion by heat-sink welding is investigated by thermal elastic-plastic analysis. It is concluded that angular distortion is reduced by additional cooling with the appropriate cooling position, and the effect of welding conditions on reduction of angular distortion are clarified by associated with heat input parameter.
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