• Proceedings of the KWS Conference
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• 1997.05a
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• pp.125-128
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• 1997

• Proceedings of the KWS Conference
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• 1999.10a
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• pp.51-54
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• 1999

• Proceedings of the KWS Conference
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• 1995.10a
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• pp.242-247
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• 1995

• Proceedings of the KSR Conference
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• 2003.10c
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• pp.73-78
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• 2003

The residual stresses and. distortions of structures by welding exert negative effect on the safety of railroad structures. This investigation performs a thermal elasto-plastic analysis using finite element techniques to evaluate residual stresses in butted-welded joint. Considering this initial residual stresses, local stress and strain at the critical location (weld toe) during the loading were analyzed by elastic plastic finite element analysis. Fatigue crack initiation life and fatigue crack propagation life of butt-welded specimen were predicted by local strain approach and Neuber's role and Paris law. It is demonstrated that fatigue life estimates by local strain approach closely approximate the experimental results.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.146-156
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• 2020

Two High Tensile Strength Steel (EH47) plates with thickness of 70 mm were butt-welded together by multi-pass Submerged Arc Welding (SAW), also the hardness and welding residual stress were investigated experimentally. Based on Thermal-Elastic-Plastic Finite Element (TEP FE) computation, the thermal cycles during entire welding process were obtained, and the HAZ hardness of multi-pass butt welded joint was computed by the hardenability algorithm with considering microstructure evolution. Good agreement of HAZ hardness between the measurement and computational result is observed. The evolution of each phase was drawn to clarify the influence mechanism of thermal cycle on HAZ hardness. Welding residual stress was predicted with considering mechanical response, which was dominantly determined by last cap welds through analyzing its formation process.

• Nuclear Engineering and Technology
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• v.56 no.10
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• pp.4184-4194
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• 2024

New technologies in polymer synthesis and pipe extrusion equipment have led to the commercialization of high-performance, large-diameter, thick-wall high density polyethylene (HDPE) pipes. They have been used in the field of seawater transport and cooling to replace metal pipes, due to their advantages of high corrosion resistance and extensibility. Connection of HDPE pipe is important as it determines the safety of the entire piping system. Butt fusion welding is commonly used for HDPE pipe connection but may cause the formation of weak points in the welded joints, interfering the reliability of the pipeline system in the application of nuclear power plants. At present, there is a lack of research on evaluating the performance of welded joint for large-diameter thick-wall HDPE pipes made by butt fusion-welding. The purpose of this study is to investigate the influence of three different butt fusion-welding processes, i.e., single low pressure (SLP), single high pressure (SHP) and dual low pressure (DLP), by evaluating the performance of their welded joints, including characterizing tensile strength, extensibility, crystallinity and hardness. In specific, a thick-wall HDPE pipe with OD of 812.8 mm and wall thickness of 74 mm which is certified for nuclear safety class was used for study. Representative specimen from the outer, middle and inner part across the wall of the main pipe body and welded joints were taken for testing. Different test methods and specimens were designed to assess the feasibility of evaluating the welding performance from different welding process. The results showed that the mechanical properties of different locations of the welded joints were different, and the tensile strength and fracture energy of the middle part of the joint were lower than that of the inner and outer parts, which could be caused by the difference in the crystallinity and thickness of the melting zone influenced by welding processes, as can be seen from the analysis of DSC test and morphology observation. Hardness testing was conducted on the section of the welded joints, and it revealed that the micromechanical properties of the welded joints in the region of the heat-affected zone were enhanced significantly, which may be due to the annealing effect caused by welding process. In summary, The DLP process resulted in the best extensibility of the welded joints among three processes, suggesting that the joining pressure from welding process plays an important role in affecting the extensibility of the welded joints.

• Journal of the Korean Society for Nondestructive Testing
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• v.15 no.2
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• pp.378-385
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• 1995

The ultrasonic non-destructive testing uses the directivity of the ultrasonic pulse wave which propagates in one direction. The directivity is expressed as the relationship between the propagate direction and its sound pressure. The directivity of ultrasonic wave is closely related to determination of probe arrangement, testing sensitivity, scanning pitch and defect location and characterization. The paper measured the directivity of shear wave, which reflected from artificial defect located in weld metal zone in butt welded joint similar model made of pyrex glass by using visualization method. 2 MHz and 4 MHz angle probes were used to measure the directivity of reflection wave at the artificial defect. The directivity of shear waves reflected from the defect was different according to the probe position and the shape of butt welded joint. The difference of directivity of reflection wave was existed between 2 MHz and 4 MHz angle probes. The angle of reflection wave became equal to angle of incidence as increase of the height of excess metal.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.8
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• pp.1061-1068
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• 2012

These days, world wide interest about global warming and environmental pollution and exhausting fossil fuel which have been main energy source in all around the world. So many country have tried to find out the solution by investing new & renewable and clean energy. Therefore LNG have been widely used as a substitution of fossil fuel and clean energy that emits less pollutant like SOx, NOx. Therefore LNG consumption has been quickly raised and LNG carriers have been getting larger for decades. In this study, high power fiber laser was used for welding of stainless steel for LNG carrier to increase its productivity. Used material was STS316L which has low carbon less than 0.03% and its thickness was 8 mm. We carried out bead, lap and butt welding by using the fiber laser which has maximum power up to 5kW. As a result, we could find out that lap and butt joint was possible at welding speed of 2.0m/min and 3.0m/min respectively.

• Journal of Welding and Joining
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• v.26 no.5
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• pp.29-35
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• 2008

In this paper concentrate on the comparison of the thermal and mechanical characteristics in Butt joint of ship structure AH32 steel by using hybrid welding and conventional SAW. For this purpose, fundamental welding phenomena of hybrid process using $CO_2$ Laser and MIG is investigated by the experiments and characteristics of thermal and welding residual stress distribution of welded joint in SAW and hybrid welding are understood from the result of FE numerical simulation and experimental values. From the result of this study, it is understood that Laser-MIG hybrid welding have high potential, make substantial saving of time and manufacturing cost and may proves its self robust in the butt joining of thick AH32 steel ship structural plate in the near future.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.127-132
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• 2002

Recent deepwater offshore structures in Gulf of Mexico utilize butt welded tubular joints. Application of welded tubular joint includes tendons, production risers, and steel catenary risers. Fatigue life assessment of these joints becomes more critical because the structures to which they are attached are allowed to undergo cyclic and sometimes large displacements around an anchored position. Estimating the fatigue behavior of these tubular members in the design stage is generally conducted by using S-N curves specified in the codes and standards. Applying the stress concentration factor of the welded structure to S-N approach often results in very conservative assessment because the stress field acting on the tubular has a non-uniform distribution through the thickness. Fracture mechanics and fitness for service (FFS) technology have been applied in the design of the catenary risers. This technology enables the engineer to establish proper requirements on weld quality and inspection acceptance criteria to assure satisfactory structural integrity during its design life. It also provides guidance on proper design curves to be used and a methodology for accounting for the effects of non-uniform stress distribution through the wall thickness. An attempt was made to develop set of S-N curves based on fracture mechanics approach by considering non-uniform stress distribution and a threshold stress intensity factor. Series of S-N curves generated from this approach were compared to the existing S-N curves. For flat plate butt joint, the S-N curve generated from fracture mechanics matches with the IIW class 100 curve when initial crack depth was 0.5 mm (0.02"). Similar comparison with API X′ was made for tubular joint.. These initial crack depths are larger than the limits of inspection by current Non-destructive examination (NDE) means, such as Automatic Ultrasonic Inspection (AUT). Thus a safe approach can be taken by specifying acceptance criteria that are close to limits of sizing capability of the selected NDE method. The comparison illustrates conservatism built into the S-N design curve.