• Journal of the Korean Institute of Gas
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• v.10 no.2 s.31
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• pp.61-67
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• 2006

We developed the ultrasonic phased array technique for obtaining ultrasonic images of electrofusion joints of polyethylene piping. And we inspected 4 cases at fields with this technique. First case is for the 300 mm diameter polyethylene electrofusion joint by using 3.5 MHz phased array sensor, second is for the 350 mm diameter saddle electrofusion joint, third is for the 400 mm diameter electrofusion joints and the last one is for the 400 mm diameter piping joints which will be used at 300 kPa suppling pressure.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.9 no.1
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• pp.8-14
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• 2013

Steam turbine blades and discs of nuclear power plants are one of the most highly stressed areas of turbine rotor, and periodic inspection of the blade roots is essential for monitoring integrity and preventing turbine failure. Ultrasonic technique is applied for volumetric inspection of blade root. However, the complexity of blade root geometry imposes challenges to inspection of blades and discs. Recently, phased array ultrasonic inspection technology is being applied to numerous power generation inspection applications including turbine rotor. The phased array ultrasonic technique requires customized inspection wedges which are generally necessary to generate effectively higher incident angle. But the usage of this wedge can cause access limitation for the lower stage blades of turbine because of the wedge front length. Therefore, the shear wave phased array probe which can generate high inspection angle without wedge is essentially necessary. In this study, feasibility study is conducted for the shear wave phased array ultrasonic probe application to blade and disc inspection. As results, the experimental results show that the shear wave phased array probe can detect the flaw and measure its size with reliable accuracy. Therefore if this shear wave phased array probe is applied to field inspection of blade and disc, more reliable inspection is expected for turbine having access limitation.

• 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.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.6 no.1
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• pp.78-82
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• 2010

The feeder pipe of Main Primary Heat Transfer System in Wolsong Nuclear Power Plant was inspected by the Ultrasonic Phase Array technique in 2010. It is the first time to apply this method to the construction at Nuclear Power Plant in Korea. The time required for UT technique is less than RT method. The UT method doesn't need to evacuate personnel who works nearby inspecting area and doesn't need to wait developing of film. For these reasons, the UT method is the fastest method among the volumetric inspections. As a result of the examination, it became clear that main defect of the feeder pipe is the Lack of fusion in the welded area. Moreover, the rate of defect was reduced gradually as improvement of welder's skill. If welding machine has problem, the defect has tended to same pattern(occurred same position in the welding area) but these defects were founded without specific rules. For these reasons, the creation of defect is dependent on the skill of worker not on the automatic welding machine. This evaluation of defect signal and collecting data would be useful to further examination in ISI.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.4
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• pp.368-375
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• 2013

Failure of small bore piping welds is a recurring problem at nuclear power plants. And the socket weld cracking in small bore piping has caused unplanned plant shutdowns for repair and high economic impact on the plants. Consequently, early crack detection, including the detection of manufacturing defects, is of the utmost importance. Until now, the surface inspection methods has been applied according to ASME Section XI requirements. But the ultrasonic inspection as a volumetric method is also applying to enforce the inspection requirement. However, the conventional manual ultrasonic inspection techniques are used to detect service induced fatigue cracks. And there was uncertainty on manual ultrasonic inspection because of limited access to the welds and difficulties with contact between the ultrasonic probe and the OD(outer diameter) surface of small bore piping. In this study, phased array ultrasonic inspection technique is applied to increase inspection speed and reliability. To achieve this object, the 3.5 MHz phased array ultrasonic transducer are designed and fabricated. The manually encoded scanner was also developed to enhance contact conditions and maintain constant signal quality. Additionally inspection system is configured and inspection procedure is developed.

• Journal of the Korean Society for Nondestructive Testing
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• v.35 no.4
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• pp.268-274
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• 2015

Weld overlay was first used in power plants in the US in the early 1980s as an interim method of repairing the welds of flawed piping joints. Weld overlaid piping joints in nuclear power plants must be examined periodically using ultrasonic examination technology. Portable phased array ultrasonic technology has recently become available. Currently, the application of preemptive weld overlays as a mitigation technique and/as a method to improve the examination surface condition for more complex configurations is becoming more common. These complex geometries may require several focused conventional transducers for adequate inspection of the overlay, the original weld, and the base material. Alternatively, Phased array ultrasonic probes can be used to generate several inspection angles simultaneously at various focal depths to provide better and faster coverage than that possible by conventional methods. Thus, this technology can increase the speed of examinations, save costs, and reduce radiation exposure. In this paper, we explain the general sequence of the inspection of weld overlay and the results of signal analysis for some PAUT (phased array ultrasonic testing) signals detected in on-site inspections.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.8 no.2
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• pp.7-13
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• 2012

A spacer grid which is one of the most important structural components in a pressurized water reactor fuel is an interconnected array of slotted grid straps, welded at the intersections to form an egg-crate structure. The spacer grid is required to not only protect fuel rods stably but also have sufficient lateral crush strength for the sake of enabling shut-down of the nuclear reactor during abnormal operating environments. Then, the lateral crush strength of the spacer grid is closely related with welding quality of the spacer grid. Previous research on the crush strength analysis of the spacer grid had been performed using only parent material properties. In this study, to investigate the effect on the crush strength of the spacer grid when used mechanical properties in weld zone instead of parent material properties, crush strength analysis considering mechanical properties in weld zone obtained from the instrumented indentation technique was performed and compared the results with the previous research.

• Journal of the Korean Institute of Gas
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• v.8 no.3 s.24
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• pp.31-36
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• 2004

Electrofusion(EF) joints have been widely used as they are easy to fuse and suitable for high-quality joints for polyethylene(PE) pipes. This paper studies the cause of defects and classifies 5 types of defects. The defect detection technique for electrofusion joints of polyethylene piping is utilized by the ultrasonic phased array technique to obtain ultrasonic images of electrofusion joints. Test sample joints have been designed and fabricated using artificial defects which were made using paper. Finally, we studied the condition of electrofusion in the field and analyzed the main causes of defects. And we classified the defect types as local lack of fusion, sand inclusion, voids or air inclusion, short stab, excess penetration or excess bead.