• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.1
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• pp.11-17
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• 2015

High-density polyethylene (HDPE) piping, which has recently been applied to safety class III piping in nuclear power plants, can be butt-joined through the thermal fusion process, which heats two fused surfaces and then subject to axial pressure. The thermal fusion process generates bead shapes on the butt fusion. The stress concentrations caused by the bead shapes may reduce the fatigue lifetime. Thus, investigating the effect of the thermal butt fusion beads on fatigue behavior is necessary. This study examined the fatigue behavior of thermal butt fusion via a tensile fatigue test under stress-controlled conditions using finite element elastic stress analysis. Based on the results, the presence of thermal butt fusion beads was confirmed to reduce the fatigue lifetime in the low-cycle fatigue region while having a negligible effect in the medium- and high-cycle fatigue regions.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.11 no.2
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• pp.40-44
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• 2015

The fatigue behavior of thermal butt fusion in safety class III high-density polyethylene (HDPE) buried piping for nuclear power plants was investigated using load-controlled bending fatigue on four-point bend test specimens. Based on the results, the presence of thermal butt fusion beads was confirmed to reduce the fatigue lifetime in the low- and medium-cycle fatigue regions while having a negligible effect in the high-cycle fatigue regions.

• Nuclear Engineering and Technology
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• v.51 no.4
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• pp.1142-1153
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• 2019

This paper presents the effect of fusion procedure on the fusion performance of the thermal butt fusion in the safety class III buried HDPE piping per various tests performed, including high speed tensile impact, free bend, blunt notched tensile, notched creep, and PENT tests. The suitability of fusion joints and qualification procedures was evaluated by comparing test results from the base material and buttfusion joints. From the notched tensile test result, it was found that the fused joints have much lower toughness than the base material. It was also identified that the notched tensile test is more desirable than the high speed tensile impact and free bend tests presented in the ASME Code Case N-755-3 as a fusion qualification test method. In addition, with regard to the single low-pressure fusion joint performances, the procedure given by the ISO 21307 was determined to be better that the one specified in the Code Case N-755-3.

• Journal of Welding and Joining
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• v.29 no.1
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• pp.85-89
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• 2011

Waste water is disposed to sewage disposal plant by underground PE double wall pipes. Various processes have been introduced to join PE pipes, but most of these methods have many disadvantages such as costs, lack of reliability and difficulties in joining, etc. Recently butt welding has been paid much attention to joint PE pipes as this process has many advantages such as cost, safety and reliability. In this study, newly developed heat plate, a patent-pending heat plate with a groove, was used to butt-weld PE double wall pipes with different misalignment gaps to simulate real underground conditions, and the butt welding temperature of PE pipe was determined by thermal analysis (Thermal Gravimetric Analysis, Differential Scanning Calorimetry and Dynamic Mechanical Analysis). The resulting joining characteristics of double wall pipes were compared with those from a conventional heat plate, in terms of stiffness, flattening and leakage tests. The results from the stiffness and flattening test showed that there were no big differences between the butt-welded joints made from these two plates. From the leakage test, although PE pipes welded with a conventional heat plate did leak below the required test conditions (10 min. at 0.75kgf/cm2), the pipes welded with a patent-pending grooved heat plate did not show any leakage even at a pressure 1.5 times higher than the required conditions. It was noted that by utilizing a grooved heat plate more complete fusion at the pipe joints could be obtained, which in turn induced a high quality joints.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.2
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• pp.165-173
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• 2004

Laser beam welding is increasingly being used in welding of structural steels. The laser welding process is one of the most advanced manufacturing technologies owing to its high speed and deep penetration. The thermal cycles associated with laser welding are generally much faster than those involved in conventional arc welding processes, leading to a rather small weld zone. Experiments are performed for 304 stainless steel plates changing several process parameters such as laser power, welding speed, shielding gas flow rate, presence of surface pollution, with fixed or variable gap and misalignment between the similar and dissimilar plates, etc. The following conclusions can be drawn that laser power and welding speed have a pronounced effect on size and shape of the fusion zone. Increase in welding speed resulted in an increase in weld depth/ aspect ratio and hence a decrease in the fusion zone size. The penetration depth increased with the increase in laser power.

• Journal of Welding and Joining
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• v.31 no.1
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• pp.51-57
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• 2013

Residual stress caused in the weldments with high restraint force are often observed during welding in the weldments of Inner and outdoor materials or radial tanks. The reason is that quantitative analysis about thermal stresses during laser welding is lacking for this weldments. To verify Finite Elements Method (FEM) theory, the temperature was measured with thermocouple in a real time in this paper. Also analysis of the thermal stress for welding condition is performed by Comsol program package on various welding condition in SCP1-S butt welding. The principal stress in laser welding process is seen through the width direction. Also, it was confirmed that a change in base metal by thermal expansion made the stress in width direction stronger. Base metal close to the weld bead as the process progresses to the tensile stress in the compressive stress was varied. It was shown that the change of stress was quantitative from the bead at a certain distance.

• Proceedings of the KWS Conference
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• 1994.05a
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• pp.222-225
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• 1994

The weldability of aluminum is excel lent but weld metal is subject to include weld defects such as porosities, crack, incomplete penetration and incomplete fusion because of improper welding parameters. Especially, the porosities are main weld defects because the difference of hydrogen solubility change in melt ins and solidification state with temperature changing. Deformation of aluminum is larger than mi Id steel due to higher thermal conductivity. It is reported that porosities in deposited metal affect tensile strength and elongation. Therefore, the effect of groove angle on porosities and mechanical properties of weld metal were researched in this report where Al-5083 plate was used with 5356 filler metal that are excellent anti corrosion and strength.

• Proceedings of the KWS Conference
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• 2010.05a
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• pp.59-59
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• 2010

Friction stir welding has become a viable and important manufacturing alternative or fabrication component, especially in aerospace and automobile applications involving aluminium alloys. In recent years, there is an increasing interest for FSW of dissimilar metals and alloys, particularly systems which are difficult to weld by conventional, thermal (or fusion) welding. In this study we tried to analyse the complex heat distribution occurring in TIG assisted FSW of dissimilar butt joint (STS304 and Al6061). For this, an analytical model for heat generation by FSW based on contact conditions has been developed. The heat input was calculated considering the coefficient of friction and slip factor between each work piece material with the tool material. The thermal model is used to generate the temperature characteristics curve, which successfully predicts the maximum welding temperature in each alloys. The analysis was carried out using the in-house solver.

• Journal of Power System Engineering
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• v.18 no.4
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• pp.85-90
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• 2014

In this paper, the transient thermal and residual stress analysis of the welding of 9% Ni steel plates using the FEA software ABAQUS are presented. The 9% Ni steel plates are welded manually with welding consumables of 70% Ni based Inconel type super-alloys (YAWATA WELD B (M)), producing a multi-pass/multi-layer butt weld. For these materials, temperature dependant mechanical and thermal material properties are used in the analysis. The back gouging is considered in welding process simulation. The FE thermal results are validated by comparing the real fusion profile and heat affected zone (HAZ). In addition, the continuous indentation test was conducted to measure the strength of base metal, HAZ and weld metal.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1560-1565
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• 2005

Laser beam welding is increasingly being used in welding of structural steels. The laser welding process is one of the most advanced manufacturing technologies owing to its high speed and deep penetration. The thermal cycles associated with laser welding are generally much faster than those involved in conventional arc welding processes, leading to a rather small weld zone. Experiments are performed for 304 stainless steel plates changing several process parameters such as laser power, welding speed, shielding gas flow rate, presence of surface pollution, with fixed or variable gap and misalignment between the similar and dissimilar plates, etc. The following conclusions can be drawn that laser power and welding speed have a pronounced effect on size and shape of the fusion zone. Increase in welding speed resulted in an increase in weld depth/ aspect ratio and hence a decrease in the fusion zone size. The penetration depth increased with the increase in laser power.