• Journal of Welding and Joining
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• v.21 no.3
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• pp.85-91
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• 2003

Narrow gap welding has many advantages over conventional V-grooved butt welding such as high productivity, small deformation and improved mechanical property of joints. With narrower groove gap, less arc heat input is expected will all the other advantages of narrow gap welding. The main defects of narrow gap welding include the lack of root fusion, convex bead surface and irregular surface, all of which have negative effects on the next welding pass. This paper suggests an up-and-down torch oscillation for ultra narrow gap welding with gap size of 5mm and investigates the proper welding conditions to fulfill the reliable and high welding quality. First, GMA welding model was suggested for ultra narrow gap welding system with Halmoy's model referenced for wire melting modeling. And the arc length in ultra narrow gap was defined. Secondly, based on the experimental results of up-and-down torch oscillation welding, phase shift of current and wire extension length were simulated for varying oscillation frequency to show that weld the bead shape in ultra narrow gap welding can be predicted. As the result, it was confirmed that reliable weld quality in ultra narrow gap welding can be achieved with up-and-down torch oscillation above 15Hz due to its ability to provide uniform heat input along the sidewall of gap.

• Journal of Welding and Joining
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• v.34 no.1
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• pp.68-74
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• 2016

Adoption of narrow gap welding shall be increased for the butt joint of thick plate, because the deformation and welding cost is reduced by decrease of cross-sectional area. However, sometimes narrow gap causes defects such as lack of fusion since it has small groove angle and narrow groove width. Therefore, GMAW, GTAW and SAW process shall be adopted to narrow gap welding with small bead hight and low deposition rate. In this study, Super-TIG welding using C-type strip was applied to semi-narrow gap butt joint in order to increase the welding productivity. High deposition rate 10kg/hr was obtained by high current 600A without undercut, humping bead and other welding defects. Measuring the mean and standard deviation of the melting depth to evaluate the developed processes, the fusion line type was determined by measuring the difference between maximum and minium melting depth. Furthermore, a model on arch fusion line and linear fusion line was suggested in order to prevent LF on groove wall in narrow gap butt welding.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.670-677
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• 2003

Although Gas Tungsten Arc Welding (GTAW or TIG welding) is considered as high quality and precision welding process, it also has demerit of low melting rate. Narrow-gap TIG welding which has narrow joint width reduces the groove volume remarkably, so it could be shorten the welding time and decrease the overall shrinkage in heavy wall pipe welding. Generally Narrow-gap TIG welding is used as orbital welding process, it is important to select the optimum conditions for the automatic control welding This paper looks at the application and metallurgical properties on Narrow-gap TIG welding joint of heavy wall large austenitic stainless steel pipe to determine the deposition efficiency, the resultant shrinkage and fracture toughness. The fracture toughness depends slightly on the welding heat input.

• International Journal of Korean Welding Society
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• v.2 no.1
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• pp.45-51
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• 2002

In the multi-pass welding of pressure vessels or ships, the mechanical touch sensor system is generally used together with a manipulator to measure the gap and depth of the narrow gap to perform seam tracking. Unfortunately, such mechanical touch sensors may commit measuring errors caused by the deterioration of the measuring device. An automation system of narrow gap multi-pass welding using a laser vision system which can track the seam line of narrow gap and which can control welding power has been developed. The joint profile of the narrow gap, with 250mm depth and 28mm width, can be captured by laser vision camera. The image is then processed for defining tracking positions of the torch during welding. Then, the real-time correction of lateral and vertical position of the torch can be done by the laser vision system. The adaptive control of welding conditions like welding currents and welding speeds, can also be performed by the laser vision system, which cannot be done by conventional mechanical touch systems. The developed automation system will be adopted to reduce the idle time of welders, which happens frequently in conventional long welding processes, and to improve the reliability of the weld quality as well.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.706-713
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• 2002

In the multi-pass welding of pressure vessels or ships, the mechanical touch sensor system is generally used together with a manipulator to measure the gap and depth of the narrow gap to perform seam tracking. Unfortunately, such mechanical touch sensors may commit measuring errors caused by the eterioration of the measuring device. An automation system of narrow gap multi-pass welding using a laser vision system which can track the seam line of narrow gap and which can control welding power has been developed. The joint profile of the narrow gap, with 250mm depth and 28mm width, can be captured by laser vision camera. The image is then processed for defining tracking positions of the torch during welding. Then, the real-time correction of lateral and vertical position of the torch can be done by the laser vision system. The adaptive control of welding conditions like welding Currents and welding speeds, can also be performed by the laser vision system, which cannot be done by conventional mechanical touch systems. The developed automation system will be adopted to reduce the idle time of welders, which happens frequently in conventional long welding processes, and to improve the reliability of the weld quality as well.

• Proceedings of the KWS Conference
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• v.43
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• pp.76-78
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• 2004

The phenomenon of weld shrinkage mainly occurs owing to residual stress by heating, which largely effects on welding quality, Actually as the shrinkage rate depends on the weld deposit amount, so it is desired that the sectional area of weld joint shall be reduced. In this respect the Electron beam welding has more profitable position compare to Narrow-gap TIG welding which is even superior to other arc welding processes. In case of thick austenitic stainless steel the shrinkage rate of Electron beam welding has about $10\%$ of Narrow-gap TIG welding's, which means that residual stress is a lot less than that of Narrow-gap TIG welding. And heat input and welded section area also indicate large difference between two processes.

• Journal of Welding and Joining
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• v.2 no.1
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• pp.58-65
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• 1984

NGW(Narrow Gap Welding)는 개선폭이 약 9mm로서 연강 및 저탄소강을 용접할 경우 두께가 300mm까지 1층으로 용접이 가능하다. 따라서 두께가 두꺼운 발전설비, 원자력 설비, 화학 설비 등의 압력용기의 용접에 적합한 용접법이다. 그러나 실제적인 NGW의 적용은 제작자의 친근 감의 결여, 기술 부족 및 복잡성 등의 이유로 아직도 비교적 널리 활용되지 않고 있다. 새로운 type의 GMAW-NG process가 발전되어 오고 잇다. 위와 같은 장점과 단점을 비교해 볼 때 낮은 operating 경비, 높은 joint filling rate, 변형과 잔류 응력의 감소 등으로 세계적인 용접 전 문가들의 계속적인 관심도가 높아지고 사용도도 증가하고 있다. narrow gap welding의 장단점을 요약하면 아래와 같다. 장 점 1) 생산성이 높다. 2) 고품질을 얻을 수 있다. 3) 잔류 응력과 변형을 적게 한다. 4) 전자세 용접이 가능하다. 단 점 1) 용접기의 가격이 비싸다. 2) 용접 품질에 큰 영향을 주는 아아크가 작업 조건에 따라 민감하게 변한다. 3) repair procedure는 다른 용접 방법을 요구한다. 4) 과도한 복잡성 때문에 장비의 신뢰성이 낮다.

• Journal of Welding and Joining
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• v.4 no.1
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• pp.40-46
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• 1986

This investigation studied the toughness variations in the narrow gap weldment with the notch location. Specimens with the notch at the center of the weld metal showed the lowest toughness. As the location of notchmoves to fusion line, the impact properties improve reaching a maximum at the fusion boundaries. This improvement in toughness can be explained by the microstructural feature showing in the narrow gap weldment. "one pass/layer" technique performed in narrow gap welding results in the increased proportion of refined structure as approaching to fusion boundary from weld center and thus leave 100% refined structure along the fusion boundary. HAZ also shows 100% refined structure with respect to base metal structure accompanied with the significant suppression of ductile-brittle transition temperature.mperature.

• Proceedings of the KWS Conference
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• 2005.06a
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• pp.82-84
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• 2005

Among the advanced welding processes which are superior to conventional process, Electron beam welding and Narrow-gap TIG welding are most prospective in being applicable for the heavy industry field. With STS316LN, which is high strengthened austenitic stainless steel, the characteristic evaluation for these welding processes was carried out through the mechnical tests and property analyses. For the tensile strength EBW is better while in reverse for the yield strength. In Narrow-gap TIG the distribution of hardness values has some deviation according to the thickness direction while EBW has a tendency of a litter high hardness values in weld metal. After EB welding brings the reduction of nitrogen content, in TIG welding weld metal depends on the contents of welding material. Both processes have almost austenitic structure, but weld metal of EBW is also shown terrific structure

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.342-348
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• 2002

The welding technology for production of power plant facility as for other industries has been progressing forward automation and mechanization for cost reduction and shortening of cycle time. The welding for boiler tube is automated or mechanized as the parts and subassemblies of tubes are conveyed automatically in the shop. The temperature of boiler stearn is being progressively increased for higher plant efficiency. The welding of nuclear component is characterized by heavy thickness and narrow gap Submerged Arc Welding. Narrow gap Gas Metal Arc Welding and Electron Beam Welding is applied to turbine diaphragm. To improve the resistance of solid particle erosion of turbine blade and nozzle partition, HVOF spray technology and boriding process has been applied.