• Journal of Welding and Joining
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• v.33 no.4
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• pp.30-36
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• 2015

Austenite stainless steel(SA213-TP347H) has widely been used for the superheater & reheater tube in USC(ultra-supercritica) coal boiler because of its high creep rupture strength and anti-oxidation. But recently, the short-term failures have happened frequently in heat affected zone for only 4,000~15,000hours of service. Many investigations have been conducted to understand the failure mechanism. The root cause of failure was comfirmed to "strain induce participation hardening crack" or "reheat cracking". This mechanism often occurred due to weld residual stress and precipitation of the Cr, Nb carbides in the stabilized stainless steel such as TP347H. This paper presents an analysis of failure tube and effect of the sample tubes that conducting stabilizing heat treatment in site after 11,380hours & 16,961hours of service. Visual inspection was performed. In addition, microscopic characteristics was identified by O.M, SEM, and hardness test was carried out to find out the heat treatment effects. Failures seem to happen because of being not conducted stabilizing heat treatment in site. And another cause is inadequate weld parameter such as pass, ampere, voltage, inter-pass temperature. Thus, this paper has the purpose to describe that how to prevent similar failures in those weld-joints.

• Journal of the Society of Naval Architects of Korea
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• v.34 no.1
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• pp.68-76
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• 1997

The welding-induced initial imperfections such as residual stresses and initial strains in plated structures of ships and offshore structures can be effectively evaluated by the thermal elasto-plastic analysis method proposed in this paper. In the analysis of heat conduction of plate structures, both the analytical method and the numerical method are used. For the thermal elasto-plastic analysis of plates, the finite element analysis is performed, based on the initial strain method. In the plastic domain during incremental process, the 2nd order terms of stress increments and yield stress increments were considered, so that time increment could be controlled for more stable solution. To measure temperature distribution and angular distortion of plates during welding, bead-on-plate experiment are perform with various heat input and plate thickness. Measured data show good agreement with the calculated results.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.4
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• pp.908-917
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• 1995

The constant .DELTA.K fatigue tests are performed in SS41 and its weldments to investigate crack opening behavior and fatigue crack propagation behavior at each parts of weldment and its boundary layer. The weldments were annealed after welding for the purpose of relieving residual stress. Every weldments has notch at weld metal zone, and fatigue crack propagates from weld metal zone to vase metal zone perpendicular to weld line. The Laser ISDG method is used in order to determine the crack opening ratio, this method is more precise than indirect measurement method, and faster and easier than other direct measurement method.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.266-272
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• 2002

This study reviews the factors controlling the weld metal cracking and shows the difference from those of HAZ cracking. It further reviews the recent progresses made in consumable design for improving the crack resistance in the high strength weld metal. Previously the controlling factors for weld metal cracking were regarded as weld metal strength, diffusible hydrogen and weld metal height. However an overall review presented in this article shows that the cold crack resistance can be improve significantly through the microstructural control and that an increase in tensile strength is not necessarily related to a decrease in the resistance to cold cracking.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.1
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• pp.47-54
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• 2013

This study investigates the crack growth behavior due to primary water stress corrosion cracking (PWSCC) in the dissimilar metal butt weld of a reactor piping using Alloy 82/182. First, detailed finite element stress analyses were performed to predict the stress distribution of the dissimilar metal butt weld in which the hydrostatic and the normal operating loads as well as the weld residual stresses were considered to evaluate the stress redistribution due to mechanical loadings. Based on the stress distributions along the wall thickness of the dissimilar metal butt weld, the crack growth behavior of the postulated axial and circumferential cracks were predicted, from which the crack growth diagram due to PWSCC was proposed. The present results can be applied to predict the crack growth rate in the dissimilar metal butt weld of reactor piping due to PWSCC.

• Journal of the Korean Institute of Gas
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• v.4 no.1 s.9
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• pp.55-62
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• 2000

A surface acoustic wave method for the evaluation of small fatigue crack initiated from a pit-type surface flaw is presented. In-situ ultrasonic experiments are performed for aluminum 2024-T3 alloy samples under the fatigue test. During the fatigue test, the surface acoustic wave reflection signal from the pit and crack is measured under different hold-stress levels. From the measured and predicted surface wave reflections the depths of fully and partially open cracks are determined and results are verified by comparing with SEM fractography The crack opening behavior of the fatigue crack is evaluated from the predicted effective crack depths. The method developed in this study can be applied to monitor and characterize crack initiation and propagation from pit-type surface flaws in the early stage of fatigue life.

• Journal of Ocean Engineering and Technology
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• v.19 no.6 s.67
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• pp.64-71
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• 2005

The welding methods have been applied to the most structural products used in the automobile, ship construction, and construction. The structure steel must have sufficient strength of structure; However, the mechanical properties of the welded part changes when it is welded. Therefore, the stability or life of the structure may be affected by the changed mechanical properties. The mechanical properties of the welded part must be examined in order to ensure the safety of structure. In this research, the SS400 steel and the STS304 steel were used to estimate the mechanical properties of the HAZ by weld thermal cycle simulation. In this study, the materials were used to examine the weld thermal cycle simulation characteristic, under two conditions: the drawing with diameter of $\Phi$10 and the residual stress removal treatment. To examine the mechanical properties by the weld thermal cycle simulation, the tensile test was carried out in room temperature. The crosshead speed was lmm/min.

• Corrosion Science and Technology
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• v.20 no.2
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• pp.69-76
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• 2021

In this work, we have performed a corrosion failure analysis of a leaking tube connected to an upper header of a condensate pre-heater in a heat recovery steam generator. It was revealed that the leakage position in the tube was the location where the materials were easily vulnerable due to tensile residual stresses induced by the material manufacturing process and welding process. In addition to an imbalance in the module induced by temperature difference during operation of the pre-heater, the weight of the modules and thermal fatigue provoked a type of stress of tensile-tensile fatigue on the tube. Thus, the leakage position of the pre-heater was exposed to the tensile stress on the inner surface of the tube facing the gas, which rendered the unstable oxide layer susceptible to corrosion and the formation of pits on the water side. The cracks propagated along with the degraded microstructure in a transgranular cracking mode under fatigue loading and finally resulted in water leakage.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.5
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• pp.461-466
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• 2013

This paper examines the characteristics of butt welding joint shrinkage for shipbuilding and marine structures main plate. The shrinkage strain of butt welding joint which is caused by the process of heat input and cooling, results in the difference between dimensions of the actual parent metal and the dimensions of design. This, in turn, leads to poor quality in the production of ship blocks and reworking through period of correction brings about impediment on improvement of productivity. Through experiments on butt welding joint's shrinkage strain on large structures main plate, the deformation of welding residual stress in the form of I, Y, V was obtained. In addition, the results of experiments indicate that there is limited range of shrinkage in the range of 1 ~ 2 mm in 11t ~ 21.5t thickness and the effect of heat transfer of weld appears to be limited within 1000mm based on one side of seam line so there was limited impact of weight of parent metal on the shrinkage. Finally, it has been learned that Shrinkage margin needs to be applied differently based on groove phenomenon in the design phase in order to minimize shrinkage.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.4
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• pp.263-270
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• 2017

The shipbuilding industry uses large stationary tanks to store low-pressure air, which is used to open and close large shut-off valves. However, when supplying air from the tank to a distant valve, there are problems related to the need for supplementary pipes and the pressure drop during transportation. In this study, a portable welded vessel for storing high-pressure nitrogen (11 kg, 10 L, and 50 bar) was designed to prevent air leakage and improve the convenience of workers. This pressure vessel was elliptical to reduce the number of welded parts, which are structurally weak. The thickness and ratio of the major and minor axes of the pressure vessel were calculated to verify its structure stability at the working pressure (50 bar), and that the proposed weight and capacity were satisfactory. The residual stress caused by the welding process was calculated by performing a transient thermal-structural coupled field analysis using the ANSYS parametric design language (APDL), and the fatigue life of the vessel was verified based on the Goodman criterion.