• Journal of Welding and Joining
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• v.32 no.5
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• pp.7-12
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• 2014

In this study, API-X100 steel pipes were welded with various kinds of welding wires in the laser-arc hybrid welding process. 10kW fiber laser source was combined to MIG arc welding process. API X-100 steel of base metal was of 16.9mm thickness, and butt welding applied. After welding, full penetration weld was acquired by 1-pass welding. A root porosity and the lack of fusion was observed in some welding conditions. By the mixing the melted wire, acicular ferrite, polygonal ferrite, pro-eutectoid, aligned side plate, and bainite structures were observed at the weld metal. From the observation of hybrid weld, unmixed zone had more Ni and Cr. The unmixed zone was a 1/3 area of the weld metal. As the mechanical test of the hybrid welding, tensile test and impact test applied. From the tensile test, all of the welding except SM70S was fractured at the base metal. The result of the impact test at -30 degree C led 60J~320J of the absorbed energy. The result of the low-absorbed energy might be from the coarse equiaxed structures of the weld metal.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.390-395
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• 2002

The experimental and numerical study has been conducted on the sleeve repair welding of API 5L X65 pipeline. SMA W and GTAW were applied to weld the sleeve. The macrostructure and hardness of repair welds have been examined. The [mite element analysis of the multi-pass sleeve-fillet welding has been conducted to validate the experiment and investigate the effects of in-service welding conditions. The effect of gas flow rate on the hydrogen cracking was investigated. The effect of internal pressure on residual stresses and plastic strain was investigated. The allowable heat input was predicted considering the maximum temperature of inner surface of pipe and cooling rate at CGHAZ.

• Journal of Welding and Joining
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• v.19 no.3
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• pp.292-297
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• 2001

One of the major characteristics that affects the life of welded steel water pipes is the stress distribution caused by welding and external forces. Some studios have bean carried out on the residual stress of steel water pipes. But the results on the stress distributions by welding and complex external forces are rare, because real water pipes operate under the ground and many kinds of external forces act simultaneously on the joints. To understand the complex stress distributions of welded joints, therefore predictions by numerical or analytic methods are required. In this study, temperature and stress distributions in steel water pipes produced by welding are predicted by a three-dimensional finite element method(FEM). Based on these results, stress distributions by welding and complex external forces are evaluated by adopting the same numerical method. The influence of some post weld heat treatments on residual stress distributions is also investigated.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.6
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• pp.938-945
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• 2012

This research proposes FEM analysis for Tandem welding process used in wind tower and predicts optimal welding process to improve the stability of welded structures. Three dimensional elasto-plastic analyses are employed to evaluate thermo-mechanical behavior of residual stress and deformation during Tandem welding for different distance between two touches. To confirm the thermal distribution, Goldak's ellipse heat source model and the real size wind tower pipe model are utilized. Four different analyses are being performed, where in each case the distance between two electrode torches is being changed and residual stress and welding deformation are predicted. Depending on base material state, each case is divided into: Liquid (100mm), Austenite+Liquid (200mm), Austenite+Cementite (400mm), Pearlite+Cementite (800mm).

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.19 no.2
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• pp.75-83
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• 2023

For three-dimensional finite element welding residual stress simulation, several methods are available. Two widely used methods are the moving heat source model using heat flux and the temperature boundary condition model using the temperature profile of the welded beads. However, each model has pros and cons in terms of calculation times and difficulties in determining welding parameters. In this paper, a new method using the moving temperature profile model is proposed to perform efficiently 3-D FE welding residual stress analysis for large structures. Comparison with existing experimental residual stress measurement data of two-pass welding pipe and SNL(Sandia National Laboratories) mock-up canister shows the accuracy and efficiency of the proposed method.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.8
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• pp.877-885
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• 2013

A seawater pipe of the engine room in the ships is being surrounded with severely corrosive environments caused by fast flowing of the seawater, containing aggressive chloride ion and high conductivity etc.. Therefore, the leakage of the seawater from its pipe have been often occurred due to its local corrosion by aggressive chloride ions. Subsequently, its leakage area is usually welded by AC shielded metal arc welding with various electrodes. In this study, when the sea water pipe is welded with several types of electrodes such as E4301, E4311, E4313 and E4316, a difference of the corrosion resistance on the welding metal zones was investigated using an electrochemical method, observing microstructure, measuring polarization behaviors and hardness. The weld metal zone welded with E4313 electrode exhibited the lowest value of hardness compared to other weld metal zones. In addition, its zone indicated also the best corrosion resistance than those of other weld metal zones. Furthermore, all of the weld metal zones revealed a relatively better corrosion resistance than those of the base metal zones. and also showed higher hardness than the base metal zones.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.2
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• pp.97-104
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• 2007

An investigation has been made on the relationship between characteristics of Acoustic Emission (AE) signal in welding flaw and the stress corrosion defect in-service for the high pressure pipe steel. In order to tackle the problem of welding flaw in high pressure pipe, specimens were made by the aid of the application of both corrosion liquid usage and a quenching method after local heating. The amplitude of signal was $60{\sim}75\;dB$ in the territory which is suspected for defect, and the specimens which only have welding flaw showed gradients of 0.034, 0.034, 0.035. Moreover, there is a certain increase in gradient even though the differences are very slight. That is, corrosion specimens showed new gradients of 0.040, 0.039, 0.041 which put welding flaw and corrosion mechanism together. After pressurizing 3 minutes, AE signal has been detected from welding flaw easily in each part of the section. It is possible to predict the occurrence and also prevent the damage of stress corrosion crack which has characteristics of cleavage fracture.

• Korean Journal of Materials Research
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• v.21 no.1
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• pp.50-55
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• 2011

Energy resistance welding (ERW) is a pipe-producing process that has high productivity and low manufacturing cost. However, the high heat input of ERW degrades the mechanical property of the pipe. This study investigates the effect of heat input and alloying elements on microstructure and mechanical properties of ERW pipes. As the heat input increased, the ferrite amount increased. The ferrite amount in the weld centerline was larger than t at in the weld boundary. Medium carbon steels (S45C and K55) having 0.3~0.4wt.% carbon yielded a significant difference of ferrite amount in the weld centerline and weld boundary. High alloyed steels (DP780 and K55) having 1.5~1.6wt.% Mn showed a ferrite rich zone in the weld centerline. These phenomena are probably due to decarburization and demanganisation in the weld centerline. As the ferrite fraction increased, the hardness decreased a little for the S45C steels. In addition, DP780 steels and K55 steels showed that the hardness drops when those steels have a ferrite rich zone. But we demonstrated the good tensile property of the DP780 steels and K55 steels in which Mn is included.

• 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.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.5 no.4
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• pp.7-12
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• 2006

Galvanized steel pipe, copper pipe and stainless steel pipe, which is being used in waterworks piping materials. In case of galvanized steel pipe, the precipitation of a product is being generated due to the pollution of the tap water, a white water phenomenon, and various corrosion reaction because a zinc ion is melted by tap water. And in case of a cupper pipe, many problems which is harm in sanitation appeared because of a inflow of harmfulness substance by a frequent accident of a water leakage. So, to prevent these problems, it is substituted for stainless steel pipe. However, those problems is still occurring because of badness of welding, a problem of a water leakage in connection part, and a increment of construction expenses. Therefore, this research has examined the laying period according to each piping thickness and a corrosion shape according to each laying depth after laying in various soils(sandy loam, loamy, clay loam, clay) using galvanized steel pipe, copper pipe, and stainless steel pipe. That is, we has studied the data which is necessary for a rational method of preserving the quality of water by examining the corrosion properties of piping materials in the soil environment which waterworks piping materials is being used.