• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.4
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• pp.317-323
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• 2010

The manual ultrasonic examination for the nuclear power plant piping welds has been demonstrated by using KPD(Korean Performance Demonstration) generic procedure. For automated ultrasonic examination, there is no generic procedure and it should be qualified by using applicable automated equipment. Until now, most of qualified procedures used pulse-echo technique and there is no qualified procedure using phased array technique. In this study, data acquisition and analysis software were developed and phased-array transducer and wedge were designed to implement phased array technique for nuclear power plant in-service inspection. The developed procedure are qualified for performance demonstration for the flaw detection, length sizing and depth sizing. The qualified procedure will be applied for the field examination in the nuclear power plant piping weld inspection.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.4 no.2
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• pp.40-45
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• 2008

There exist many types of pipe and component fatigue through vibrations, thermal fatigues or shifting. In some cases of thermal stratification/thermal fatigue, pipes & components are receiving thermal stress by means of material expansion and shrinkage by continuous thermal repetitive variation. Small cracks initially occur on the inside surface by thermal stress. These cracks grow in depth the pipe wall and finally come to a rupture. Pipe parts of susceptibility to thermal stratification and thermal fatigue are now being examined by conventional UT(ultrasonic test) as volumetric examination. It is difficult to fully satisfy the code & standards requirements because 3" weldolet weldments of RCS 16" pipe to 3" branch connection lines have complex structural shape. To solve the problems of conventional UT examination, we made a realistic mock-up and UT calibration block. We performed a simulation of phased array UT utilizing CIVA as NDE(Non-Destructive Examination) simulation software. Also we designed phased array UT transducer and wedge, optimal frequency by using simulation data. We performed phased array UT experiment through mock-up including artificial flaws(notch). The phased array UT technique is finally developed to improve the reliability of ultrasonic test at RCS 16" pipe to 3" branch connection weld.

• Journal of the Earthquake Engineering Society of Korea
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• v.7 no.3
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• pp.69-77
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• 2003

This paper presents test results on eight reduced beam section(RBS) steel moment connections. The testing program addressed bolted versus welded web connection and panel zone(PZ) strength as key variables, Specimens with medium PZ strength were designed to promote energy dissipation from both PZ and RBS regions such that the requirement for expensive doublet plates could be reduced. Both strong and medium PZ specimens with a welded web connection were able to provide satisfactory connection rotation capacity for special moment-resisting frames. On the other hand, specimens with a bolted web connection performed poorly due to premature brittle fracture of the beam flange of the weld access hole. If fracture within the beam flange groove weld was avoided using quality welding, the fracture tended to move into the beam flange base metal of the weld access hole. Plausible explanation of a higher incidence of base metal fracture in bolted web specimens was presented. The measured strain data confirmed that the classical beam theory dose not provide reliable shear transfer prediction in the connection. The practice of providing web bolts uniformly along the beam depth was brought into question. Criteria for a balanced PZ strength improves the plastic rotation capacity while reduces the amount of beam distortion ore also proposed.

• Journal of the Korean Institute of Gas
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• v.5 no.3 s.15
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• pp.45-50
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• 2001

Open rack vaporizer (ORV) has been used in liquefied natural gas (LNG) receiving terminal in order to vaporize LNG into natural gas (NG) by heat exchange with seawater The U-type ORV which had been operated with seawater for 14 years is one of the important utilities of the gas production and the weld part of tube connected with header_ pipe had experienced many corrosion problems. To elucidate the cause of corrosion at weld part of vaporizer tube, corrosion potentials were compared by parts. This study concerns on the measurement of corrosion pit depth using non-destructive method and the evaluation of stress distribution in an aspect of safety with finite element analysis. In order to confirm the reliability of galvanic corrosion between weld parts and base metal, the measurement of corrosion potential by parts was conducted for 20 minutes in 3.5$\%$(wt.) NaCl solution. Many non-destructive methods were tried to measure the remaining thickness of vaporizer tube at fields. For general corrosion, tangential radiography test was confirmed as an effective method. In case of a fine corrosion pit, the shape of corrosion pit was reproduced using surface replication method. From collected data, stress distributions were quantitatively evaluated with 2-dimensional finite element method and the diagnostic evaluation on internal pressure of the U-type vaporizer could be made.

• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.4
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• pp.288-294
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• 2016

This paper aims to compare the ability to detect notch defects existing in the plate and welded area using a flexible ECA (eddy current array) probe with OmniScan MX and MS-5800E. The characteristics of signals with various frequencies and lift-offs were also compared. As a result, when signals of frequencies 500, 1000, and 1500 kHz were used, the amplitude of the signal increased, as the depth of the notch increased, but reduced linearly in accordance with the lift-off variation. In addition, the detection sensitivity of the weld defect was found to be closely related to the contact surface of the probe and specimen. In this paper, it was demonstrated that the detection sensitivity was excellent when the contact surface of the probe and the specimen was sufficient, but it was poor when the contact surface was insufficient.

• Journal of Welding and Joining
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• v.34 no.1
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• pp.75-81
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• 2016

This study applied laser surface melting process using CW(Continuous wave) Yb:YAG laser and cold-work die steel SM45C and investigated microstructure and hardness. Laser beam speed, power and beam interval are fixed at 70 mm/sec, 2.8 kW and $800{\mu}m$ respectively. Depth of Hardening layer(Melting zone) was a minimum of 0.8 mm and a maximum of 1.0 mm that exceeds the limit of minimum depth 0.5 mm applying trimming die. In all weld zone, macrostructure was dendrite structure. At the dendrite boundary, Mn, Al, S and O was segregated and MnS and Al oxide existed. However, this inclusion didn't observe in the heat-affected zone (HAZ). As a result of interpreting phase transformation of binary diagram, MnS crystallizes from liquid. Also, it estimated that Al oxide forms by reacting with oxygen in the atmosphere. The hardness of the melting zone was from 650 Hv to 660 Hv regardless of the location that higher 60 Hv than the hardness of the HAZ that had maximum 600 Hv. In comparison with the size of microstructure using electron backscatter diffraction(EBSD), the size of microstructure in the melting zone was smaller than HAZ. Because it estimated that cooling rate of laser surface melting process is faster than water quenching.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.1
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• pp.67-75
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• 2010

Submarine and deep sea diving structures are generally designed based on their ultimate strength. Fatigue strength at welded joint must be also taken into account because working stress is increased due to the increasing of diving depth and using high yield steel. The pressure hulls of submarine are subjected to fluctuating compressive loading. But in addition to the calculated stresses, high residual tensile stresses at welded part have to be considered. The state of stress level of pressure hull is tensile at surface and compressive at deep diving depth. This paper presents the results of an experimental investigation on the crack initiation and growth at the weld toe of T welded joints of HY-100 steel plate under constant amplitude loading. It is also investigated the phenomenon of the fatigue failure and test methods. Fatigue tests have been using real scaled local structural models of full penetration T-welded joint, which is a part of the cylindrical shell structures reinforced by ring stiffeners. Several load ratios under constant amplitude loading are considered in the tests. Crack initiation and growth characteristics are examined based on the beach marks of the cracked section of the test specimens. A design stress-life curve including the design formula is suggested according to tested data.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.8
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• pp.17-25
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• 1998

Aluminum alloys have low density, relatively high strength and yield strength, good plasticity, good machinability, and high corrosion and acid resistance. Therefore, they are suitable for large containers for the food, chemical and other industries. Large containers are often bodies of revolution consisting of shell courses, stiffening rings, heads and other elements joined by annular welds. Larger containers have longer welds and require greater leak-tightness and higher weld mechanical properties. The LNG tank consists of aluminum plates with various sizes, so its construction should by divided by several sections. Moreover, each section has its own sub-section consisted of several aluminum plates. To guarantee the quality of huge LNG tank, therefore, the precise control of plate dimension should by urgently needed in conjunction with the appropriate selection of process parameters such as cutting speed, depth of cut, rotational speed and so on. In this paper, a manufacturing system was developed to implement automatic circular tracking in height direction and automatic circular interpolation in depth of cut direction. Also, the neural network based on the backpropagation algorithm was used to predict the cutting quality and motor load related with the life time of the developed system. It was revealed that the manufacturing system and the neural network could be effectively applied to the bevelling process and to predict the quality of machined area and the motor load.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.10
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• pp.98-104
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• 2020

Recently, friction stir welding of dissimilar materials has become one of the biggest issues in lightweight and eco-friendly bonding technology. In this study, a lightweight torsion beam axle, which is an automobile chassis component, was used in the welding to cast aluminum material. The friction stir welding process of A357 cast aluminum and FB590 high-strength steel as well as the effects of the process parameters were investigated and optimized using a novel definitive screening design (DSD). ANOVA was used to predict the importance of the process parameters with 13 degradation experiments using the proposed DSD. Also, FSWed experiments were conducted using an optical microscope analysis to investigate the tensile strength behavior in the weld area. In addition to determining the interaction between the tool's rotational speed and the plunge speed, results indicate that the influence of the plunge depth was the most significant.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.3A
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• pp.375-381
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• 2008

This paper deals with the shear capacity of corrugated rib as the shear connector in composite structures. Corrugated rib is modified as perfobond rib shear connector type to evaluate the shear capacity. A total 12 push-out specimens with stud, perfobond rib, and corrugated rib connector were fabricated. Then, the influences of hole-crossing bars, concrete dowel, depth of corrugated panel and height of rib on the shear capacity were evaluated experimentally. As the results of these tests, the failure mechanisms of corrugated rib and perfobond rib specimens were associated with the bearing failure of the concrete slabs, but the failure of weld zone did not occur. The shear capacity of corrugated rib specimens improved as high to 96% compared to the perfobond rib shear connectors. Also, the hole-crossing bars were effective on the improvement of concrete dowel action, and consequently, shear capacity increased by 48%. It was also proven that the increment of the depth of corrugated panel and the height of rib increased the concrete bearing resistance, therefore increasing the shear capacity.