초초임계압 보일러 헤더용 P92 강 용접부의 크리프 특성 평가

백승세(Seung-Se Baek),김회현(Hoi-Hyun Kim),박정훈(Jung-Hun Park),권일현(Il-Hyun Kwon),유효선(Hyo-Sun Yu) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5

P92 steel weldment scheduled to use for next generation ultra super critical (USC) boiler header is assessed on creep characteristics. The test method to assess local structure of weldment is small-punch creep (SP-Creep) test, which is a kind of micro test proved the availability on evaluation of mechanical property for local structure. The results are compared with that of tensile creep test for same material and SP-Creep test for X20CrMoV121 (X20) steel weldment. The creep properties of P92 steel weldment are clearly superior than that of X20 steel weldment. Overall, the creep resistance of coarse grain HAZ is inferior to the other structures while fine grain HAZ is most superior in the P92 steel weldment. The power law relationships can be obtained for each weldment structure of USC boiler header.

Assessment of Creep Behavior of Inconel 617 Alloy Weldment by Small Punch Test

김범준(Bum Joon Kim) Korean Society for Precision Engineering 2023 한국정밀공학회지 Vol.40 No.3

In this research, the small punch (SP) test was applied to examine the local creep characteristics of a narrow gap weldment. To find the local creep property, an Ni-based 617 alloy and its narrow gap weldment. which is one of candidates for advanced fossil power plants, were employed. Thin square specimens were machined at three different locations: weld metal, base metal, and HAZ near the base metal from the Inconel 617 alloy narrow gap weldment. The results of the SPC test were evaluated. The microstructure of narrow gap weldment was observed by scanning electron microscopy and optical microscopy to investigate the effect of the microstructure on the creep properties of the weld zone. The creep rupture part of the weldment was observed by scanning electron microscopy. Finally, four different creep characteristics of the narrow gap weldment were obtained by the SPC test with good validity.

초초임계압 보일러 헤더용 P92 강 용접부의 고온 크리프 특성 평가

유효선 한국기계기술학회 2017 한국기계기술학회지 Vol.19 No.2

P92 steel weldment scheduled to use for next generation ultra super critical(USC) boiler header is assessed on creep characteristics. The test method to assess local structure of weldment is small-punch creep(SP-Creep) test, which is a kind of micro test proved the availability on evaluation of mechanical property for local structure. The results for P92 steel weldment are compared with that of tensile creep test for same microstructures of steel weldment. Overall, the creep resistance of coarse grain HAZ(CGHAZ) at 650℃ is inferior to the other structures while fine grain HAZ(FGHAZ) is most superior in the P92 steel weldment. The power law relationships can be obtained for each weldment structures(BM, ICHAZ, FGHAZ, CGHAZ and W.M) of USC boiler header

다층 양면 개선 맞대기 용접부의 각 변형 예측에 관한 연구

신상범,윤중근,Shin, Sang-Beom,Youn, Joong-Geun 대한용접접합학회 2007 대한용접·접합학회지 Vol.25 No.1

The purpose of this study is to establish the predictive method of angular distortion of the double-sided multi-pass butt weldment achieve it, the behavior of angular distortion in the butt weldment were investigated using comprehensive finite element analyses and experiments. The angular distortion in the multi-pass butt weldment strongly depends on the welding heat input(Q) and the effective bending rigidity of the weld throat. The effective bending rigidity of the first welding pass on the backing side was defined as the function of dimensionless parameter(k) and a bending rigidity of bead-on-plate weldment. Based on the results, the predictive equation for angular distortion of multi-pass butt weldment was proposed and verified by experiments.

GTAW 방법으로 용접된 316LN 스테인리스강의 고온 연속 저주파피로 수명에 영향을 주는 인자들에 대한 연구

김찬용,남수우,김대환,유우석 대한금속재료학회 2003 대한금속·재료학회지 Vol.41 No.4

The influence of weld defect on the continuous low cycle fatigue property for Type 316LN stainless steel base metal and weldment was investigated with a strain rate of 4×10_3/sec in air atmosphere. Low cycle fatigue test were conducted at temperature of 823K and 873K. Total strain amplitude was controlled to be 0.4-0.6%. The 308L stainless steel was used as the welding rod. The welding was done by the GtAW process with the welding direction perpendicular to the rolling direction of the base metal. The microstructures of the base metal and weldment are Υ phase and Υ/δ duplex-ferrite, respectively. The fatigue lives of the base metal had twice higher than those of weldment having no visible defect. From the tensile result, the uniform elongation of the base metal had twice higher than that of the weldment. For the base metal and HAZ, the fatigue lives at the same condition were reliable. But some results of the fatigue lives in the weldment had the lowest fatigue life at the same condition. From the observation of the fracture surface after fatigue tests, there were porosities and welding defects. For weldments having the many porosities and welding defects, the fatigue lives decreased 50% and 60-70%, respectively. From the observation of the microstructure near the internal crack, the internal weld defects was existed at the interface among the dendrites grown along the different direction.

저사이클 피로 영역에서의 Alloy 617 모재와 용접재의 파괴시험편에 대한 거시적 및 미시적 관찰

김선진(Seon Jin Kim),랜도 디와(Rando Tungga Dewa),김영식(Yeong Sik Kim),김우곤(Woo Gon Kim),김응선(Eung Seon Kim) 대한기계학회 2015 대한기계학회 춘추학술대회 Vol.2015 No.11

This paper presents the macro and microscopic fractography performed on fracture specimens from low cycle fatigue testings through Alloy 617 base metal and weldments. The weldment specimens were taken from GTAW pad of Alloy 617. The aims of the present study are to investigate the macro and microscopic aspects of low cycle fatigue fracture mode and mechanism of Alloy 617 base metal and the GTAWed weldment specimens. Fully axial total strain controlled tests had conducted at room temperature with total strain ranges of 0.6, 0.9, 1.2 and 1.5%. Macroscopic fracture surfaces of Alloy 617 base metal specimens showed a flat type normal to fatigue loading direction, whereas the GTAWed weldment specimens showed relatively shear/star type. The fracture surfaces of both the base metal and weldment specimens revealed the obvious fatigue striations at crack propagation regime. In addition, the fatigue crack initiation mechanism of the base metal showed a transgranular normal to fatigue loading direction, however, the GTAWed weldment specimens showed a transgranular about 45 degrees to fatigue loading direction.

저사이클 피로 영역에서의 Alloy 617 모재와 용접재의 파괴 시험편에 대한 거시적 및 미시적 관찰

김선진(Seon Jin Kim),랜도 디와(Rando Tungga Dewa),김우곤(Woo Gon Kim),김응선(Eung Seon Kim) 대한기계학회 2016 大韓機械學會論文集A Vol.40 No.6

본 논문은 Alloy 617 모재와 용접재에 대한 저사이클 피로 시험 후의 파괴 시험편에 대한 거시적 및 미시적 파면해석을 나타낸다. 용접재 시험편은 Alloy 617의 가스텅그스텐아크 용접 패드로부터 채취, 제작하였다. 본 연구의 목적은 Alloy 617의 모재와 용접재 시험편의 저사이클 파괴 모드 및 기구의 거시적 및 미시적 양상을 고찰하는 것이다. 전변형률 제어 피로시험이 상온에서 0.6, 0.9, 1.2 및 1.5%에 대하여 수행되었다. Alloy 617 모재의 거시적 파면은 피로하중 축에 수직인 평평한 형태의 양상을 보였으나, 용접재 시험편의 경우는 상대적으로 전단/별모양의 양상의 파괴를 나타내었다. 두 시험편 모두 피로균열전파 영역에서는 명확한 스트라이에이션이 관찰되었다. 한편, 모재의 피로균열은 피로 하중 축에 수직인 방향으로 결정입내를 따라 전파하였으나, 용접재 시험편의 경우 하중 축에 거의 45°의 경사진 형태의 결정입내로 나타났다. This paper investigates macro- and microscopic fractography performed on fracture specimens from low cycle fatigue (LCF) testings through an Alloy 617 base metal and weldments. The weldment specimens were taken from gas tungsten arc welding (GTAW) pad of Alloy 617. The aim of the present study is to investigate the macro- and microscopic aspects of the low cycle fatigue fracture mode and mechanism of Alloy 617 base metal and GTAWed weldment specimens. Fully axial total strain controlled fatigue tests were conducted at room temperature with total strain ranges of 0.6, 0.9, 1.2 and 1.5%. Macroscopic fracture surfaces of Alloy 617 base metal specimens showed a flat type normal to the fatigue loading direction, whereas the GTAWed weldment specimens were of a shear/star type. The fracture surfaces of both the base metal and weldment specimens revealed obvious fatigue striations at the crack propagation regime. In addition, the fatigue crack mechanism of the base metal showed a transgranular normal to fatigue loading direction; however, the GTAWed weldment specimens showed a transgranular at approximately 45° to the fatigue loading direction.

소켓 용접부 결함 검사용 초음파 자동 검사 장비 개발

이정기,박문호,박기성,이재호,임성진 한국비파괴검사학회 2004 한국비파괴검사학회지 Vol.24 No.3

대구경 배관에서 소구경 배관으로 연결하는 부위 및 배관의 방향 전환을 위해 사용하는 소켓용접부는 용입불량 및 사용기간이 경과되면서 내부로부터 진전될 수 있는 균열 등의 결함을 가질 수 있다. 그러나 지금까지 적용하고 있는 비파괴검사법인 액체침투탐상과 방사선투과검사로는 내부에 존재하는 균열성 결함의 검출이 어렵다. 본 연구에서는 소켓용접부 내부의 균열성 결함 검출을 위한 초음파 검사 기법을 확립하였고, 검사를 수행할 수 있는 초음파 탐촉자를 설계 제작하였으며, 자동으로 검사할 수 있는 검사 장비와 제어용 운영 프로그램을 개발하였다. 개발된 장비는 컴퓨터를 기반으로 하고 있으며, pulser/receiver를 내장하고 100㎒ 고속 A/D board를 사용하여 초음파 탐상기 역할을 프로그램으로 구현하였으며, ISA interface type으로 4축 제어용 motion controller를 개발하여 자동 검사를 수행하는 scanner를 제어하도록 하였으며, 검사 결과는 소켓용접부 단면을 실시간 영상으로 나타내도록 되어 있다. 인공결함 ㅅ험편의 결함을 평가한 결과 결함의 깊이가 1㎜인 결함의 평가 길이는 실제 크기보다 작게 나타내고 있으며, 결함의 깊이가 증가할수록 결함의 길이가 더 크게 평가되었다. 본 연구로 개발한 장비는 원자력 발전소나 화학플랜트에 많이 널려 있는 소켓용접부 내의 용입불량, 피로 균열 등을 검출하여 객관적인 검사 결과를 제시할 수 있으므로 설비 안전 관리 및 보수 부위 결정에 기여할 수 있을 것으로 기대된다. Socket weldment used to change the flow direction of fluid may have flaws such as lack of fusion and cracks. Liquid penetrant testing or Radiography testing have been applied as NDT methods for flaw detection of the socket weldment. But it is difficult to detect the flaw inside of the socket weldment with these methods. In order to inspect the flaws inside the socket weldment, a ultrasonic testing method is established and a ultrasonic transducer and automated ultrasonic testing system are developed for the inspection. The automated ultrasonic testing system is based on the portable personal computer and operated by the program based Windows 98 or 2000. The system has a pulser/receiver, 100 ㎒ high speed A/D board, and basic functions of ultrasonic flaw detector using the program. For the automated testing, motion controller board of ISA interface type is developed to control the 4-axis scanner and a real time iC-scan image of the automated testing is displayed on the monitor. A flaws with the size of less than 1 ㎜ in depth are evaluated smaller than its actual size in the testing, but the flaws larger than 1 ㎜ appear larger than its actual size on the contrary. This tendency is shown to be increasing as the flaw size increases. A reliable and objective testing results are obtained with the developed system, so that it is expected that it can contribute to safety management and detection of repair position of pipe lines of nuclear power plants and chemical plants.

인장하중법에 따른 STS 304 다층 맞대기 용접부의 변형 제어 특성에 관한 연구

김하근,이동주,신상범,Kim, Ha-Geun,Lee, Dong-Ju,Shin, Sang-Beom 대한용접접합학회 2010 대한용접·접합학회지 Vol.28 No.3

The purpose of this study is to develop the control technology of the welding distortion caused by Auto NG-GTA(Narrow Gap-GTA) welding process at the STS 304 multi-pass butt weldment. Heat input model for Auto NG-GTA welding process was established and verified by measuring temperature change and molten pool shape at the bead-on-plate weldment. With the heat input model developed, the effect of tension load on the welding distortion at the STS 304 multi-pass butt weldment was evaluated using the thermo-elasto-plastic FE analysis. In accordance with FEA results, the angular distortion and transverse shrinkage sharply decreased with an increase in tension load. This result indicated that tensioning method was an effective countermeasure against the welding distortion of the STS 304 multi-pass butt weldment.

CNN 기반 철도차량 차체-대차 연결부의 결함 평가기법 연구

권석진,김민수 한국산학기술학회 2020 한국산학기술학회논문지 Vol.21 No.11

The bogies of railway vehicles are one of the most critical components for service. Fatigue defects in the bogie can be initiated for various reasons, such as material imperfection, welding defects, and unpredictable and excessive overloads during operation. To prevent the derailment of a railway vehicle, it is necessary to evaluate and detect the defect of a connection weldment between the car body and bogie accurately. The safety of the bogie weldment was checked using an ultrasonic test, and it is necessary to determine the occurrence of defects using a learning method. Recently, studies on deep learning have been performed to identify defects with a high recognition rate with respect to a fine and similar defect. In this paper, the databases of weldment specimens with artificial defects were constructed to detect the defect of a bogie weldment. The ultrasonic inspection using the wedge angle was performed to understand the detection ability of fatigue cracks. In addition, the convolutional neural network was applied to minimize human error during the inspection. The results showed that the defects of connection weldment between the car body and bogie could be classified with more than 99.98% accuracy using CNN, and the effectiveness can be verified in the case of an inspection. 철도차량의 대차는 열차 주행을 위한 핵심적인 장치이다. 철도차량의 대차에서 피로결함은 운행 중 기대되지 않거나 과도한 하중, 용접결함, 재료 결함 등의 다양한 요인에 의해 발생할 수 있다. 철도차량의 사고를 방지하기 위해서 차체-대차연결부의 손상을 검출하고 발생 결함에 대한 정확한 평가가 요구된다. 이러한 철도차량의 차체-대차 연결부는 초음파 비파괴 검사를 통하여 건전성을 확보하고 있으나 결함 발생에 대한 학습기법을 이용한 판정방법이 필요하다.최근 미세한 결함이나 유사한 결함을 높은 인식율로 검출하기 위하여 딥러닝 기법에 관한 여러 연구가 진행되고 있다. 본 연구에서는 철도차량의 차체-대차 연결부의 결함 검출능력을 위하여 용접부의 인공결함 시편에 대하여 데이터베이스 구축하였으며. 웨지형 초음파 센서를 이용하여 차체-대차 연결부에 대한 비파괴 검사를 수행하였다. 부가적으로 인적 오류를 최소화하기 위하여 결함판단 학습기법인 합성곱 신경망기법(Convolutional Neural Network)을 적용하였다. 그 결과 합성곱 신경망기법 기법을 이용하여 철도차량의 차체-대차 연결 용접부의 균열을 99.98%이상 균열성 결함으로 판별할 수 있었으며 철도차량 차체-대차 연결부의 비파괴검사시 본 연구의 기술이 적용 가능함을 확인할 수 있었다.