• Title/Summary/Keyword: Wall thinning pipe

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Evaluation of Failure Behavior of a Pipe Containing Circumferential Notch-Type Wall Thinning (원주방향 노치형 감육부를 가진 배관의 손상거동 평가)

  • Kim, Jin-Weon;Park, Chi-Yong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.27 no.8
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    • pp.1295-1302
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    • 2003
  • In order to evaluate a failure behavior of pipe with notch-type wall thinning, the present study performed full-scale pipe tests using the 102mm, Schedule 80 pipe specimen simulated notch- and circular-type thinning defects. The pipe tests were conducted under the conditions of both monotonic and cyclic bending moment at a constant internal pressure of 10 MPa. From the results. of experiment the failure mode, load carrying capacity, deformation ability, and fatigue life of a notch-type wall thinned pipe were investigated, and they were compared with those of a circular-type wall thinned pipe. The failure mode of notched pipe was similar to that of circular-type thinned pipe under the monotonic bending load. Under the cyclic bending load, however, the mode was clearly distinguished with variation in the shape of wall thinning. The load carrying capacity of a pipe containing notch-type wall thinning was about the same or slightly lower than that of a pipe containing circular-type wall thinning when the thinning area was subjected to tensile stress, whereas it was higher than that of a pipe containing circular-type thinning defect when the thinning area was subjected to compressive stress. On the other hand, the deformation ability and fatigue life of a notch-type wall thinned pipe was lower than those of a circular-type wall thinned pipe.

Effect of Bend Angle on the Collapse Behavior of Locally Wall Thinned Pipe Bends (감육 곡관의 붕괴거동에 미치는 곡관 굽힘각의 영향)

  • Na Man-Gyun;Kim Jin-Weon
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.30 no.10 s.253
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    • pp.1269-1275
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    • 2006
  • The purpose of this study is to investigate the effect of bend angle on the collapse behavior of locally wall thinned pipe bends. For this purpose, the present study performed three-dimensional finite element analysis on the 30-, 60-, and 90-degree pipe bends with local wall thinning at the center of intrados, extrados, and crown, and evaluated the collapse moment for different thinning dimensions under closing- and opening-mode bending with a constant internal pressure. The results showed that, for intrados and extrados wall thinning, the reduction in the collapse moment due to local wall thinning became significant with decreasing bend angle of pipe bends. This effect of bend angle was enhanced with increasing thinning dimensions, and it was clearer fur opening-mode bending than for closing-mode bending. For crown wall thinning, however, the effect of bend angle was unclear and was less sensitive to the change of wall thinning shapes.

Geometric Characteristic of Wall-thinning Defect Causing Circumferential Crack in Pipe Elbows (원주방향 균열이 발생되는 곡관 감육부의 형상적 특성)

  • Kim, Jin Weon;Lee, Sung Ho
    • Transactions of the Korean Society of Pressure Vessels and Piping
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    • v.7 no.1
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    • pp.27-34
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    • 2011
  • The objective of this study is to classify the geometry of wall-thinning defect that causes a circumferential crack in the pipe elbows subjected to internal pressure. For this objective, first of all a criterion to determine the occurrence of circumferential cracking at wall-thinned area was developed based on finite element simulation for burst tests of pipe elbow specimens that showed axial and circumferential cracking at wall-thinned area. In addition, parametric finite element analysis including various wall-thinning geometries, locations, and pipe geometries was conducted and the wall-thinning geometries that initiate circumferential crack were determined by applying the criterion to the results of parametric analysis. It showed that the circumferential crack occurs at wall-thinning defect, which has a deep, wide, and short geometry. Also, it is indicated that the pipe elbows with larger radius to thickness ratio are more susceptible to circumferential cracking at wall-thinned area.

Effects of Thinning Length on Failure Mode of Local Wall Thinned Pipe (감육 배관의 손상모드에 미치는 감육부 길이의 영향)

  • Kim, Jin-Weon;Park, Chi-Yong;Lee, Sung-Ho;Kang, Tai-Kyung
    • Proceedings of the KSME Conference
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    • 2001.06a
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    • pp.357-362
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    • 2001
  • The pipe fracture tests were performed on 102mm-Sch.80 carbon steel pipe with various local wall thinning shapes, in order to understand failure behavior of thinned pipe. Pipe specimens were subjected to monotonic bending moment, using 4-points loading system, under internally pressurized condition. From the results of experiment, the failure mode, load carrying capacity, and deformability of local wall thinning pipe were investigated. Failure mode of thinned pipe depended on magnitude of internal pressure and thinning length as well as loading direction and thinning depth and angle. The variation in load carrying capacity and deformability of thinned pipe with length of thinned area was determined by stress type appled to thinning region and circumferential thinning angle. Also, the effect of internal pressure on failure behavior was dependent on failure mode of thinned pipe, and it promoted crack occurrence and mitigated local buckling at thinned area.

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Effect of Local Wall Thinning on Pipe Elastic Bending Compliance (국부 감육이 배관 굽힘 컴플라이언스에 미치는 영향 )

  • Ki-Wan Seo;Jae-Min Gim;Yun-Jae Kim
    • Transactions of the Korean Society of Pressure Vessels and Piping
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    • v.17 no.2
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    • pp.83-89
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    • 2021
  • The thickness of pipe can be locally reduced during operation due to wall thinning. Due to its significance on structural integrity, many non-destructive detecting techniques and assessment methods are available. In this study, the elastic bending compliance of local wall-thinned pipe is presented in terms of the wall thinning geometry: wall thinning depth, circumferential angle and longitudinal length. Elastic finite element (FE) analysis further shows that the presented equation can be used for any wall thinning shape. The proposed solution differs from FE results by less than 6% for all cases analyzed. The bending compliance increases linearly with increasing longitudinal thinning length and non-linearly with increasing thinning angle and depth.

Evaluation of the Burst Pressure for Rectangular Wall-thinning of CANDU Feeder Pipe (사각 감육을 고려한 중수로 공급자관 파열압력 평가)

  • Kwang Soo Kim;Min Kyu Kim;Doo Ho Cho;Jae Joon Jeong
    • Transactions of the Korean Society of Pressure Vessels and Piping
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    • v.17 no.1
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    • pp.28-35
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    • 2021
  • The flow accelerated corrosion (FAC) is one of significant aging and degradation mechanism and can affect structural integrity of CANDU feeder pipes. Pipe burst can occur under normal operation pressure (min. 10 MPa) if wall-thinning of the feeder pipe due to FAC is accumulated. Previous studies considered simple shapes of feeder pipe with local wall-thinning in order to conservatively assess structural integrity of wall-thinned feeder pipe. In this paper, a new FE model is developed, having an actual shape of the feeder pipe (double bent) as well as the actual wall-thinning shape and location based on the in-service inspection result. Then, the burst pressure assessment of the wall-thinned feeder pipe is performed using lower bound limit load analysis considering elastic-perfectly plastic material. In addition, an improved formulation to predict the burst pressure of the wall-thinned feeder pipe is presented and the safety margin is compared with an existing assessment method.

Fatigue Failure Behavior of Pipe Bends with Local Wall-Thinning Under Cyclic Bending Condition (반복굽힘 조건에서 감육 곡관의 피로손상 거동)

  • Yoon, Min-Soo;Kim, Jin-Weon;Kim, Jong-Sung
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.36 no.10
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    • pp.1227-1234
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    • 2012
  • In this study, fatigue tests were carried out using real-scale pipe bend specimens with wall-thinning defects under a cyclic bending load together with a constant internal pressure of 10 MPa. The wall-thinning defect was located at the extrados and the intrados of the pipe bend specimens. A fully reversed cyclic in-plane bending displacement was applied to the specimens. For the pipe bends with wall thinning at the extrados, an axial crack occurred at the crown of the pipe bend rather than at the extrados where the defect was located. In addition, the fatigue life was longer than that of a sound pipe bend predicted from the design fatigue curve in ASME Sec.III, and it was less dependent on the axial length of the wall-thinning defect. For the pipe bends with wall thinning at the intrados, a circumferential crack occurred at the intrados. In this case, the fatigue life was much shorter than that of a sound pipe bend predicted from the design fatigue curve, and it clearly decreased with decreasing axial length of the wall-thinning defect.

An Evaluation of Failure Behavior of Pipe with Local Wall Thinning by Pipe Experiment (배관실험을 통한 국부감육 배관의 손상거동 평가)

  • Kim, Jin-Won;Park, Chi-Yong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.26 no.4
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    • pp.731-738
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    • 2002
  • To understand failure behavior of pipe thinned by flow accelerated corrosion, in this study, the pipe failure tests were performed on 102mm-Sch.80 carbon steel pipe with various local wall thinning shapes, and the failure mode, load carrying capacity, and deformability were investigated. The tests were conducted under loading conditions of 4-points bending and internal pressure. The experimental results showed that the failure mode of thinned pipe depended on magnitude of internal pressure and thinning length as well as loading direction and thinning depth and angle. The variation in load carrying capacity and deformability of thinned pipe with thinning length was determined by stress type appled to the thinning area and circumferential thinning angle. Also, the effect of internal pressure on failure behavior was dependent on failure mode of thinned pipe, and it promoted crack occurrence and mitigated local buckling at thinned area.

Analysis of Pipe Wall-thinning Caused by Water Chemistry Change in Secondary System of Nuclear Power Plant (원전 2차계통의 수화학 변화가 배관감육에 미치는 영향 분석)

  • Yun, Hun;Hwang, Kyeongmo;Moon, Seung-Jae
    • Corrosion Science and Technology
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    • v.14 no.6
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    • pp.325-330
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    • 2015
  • Pipe wall-thinning by flow-accelerated corrosion (FAC) is a significant and costly damage of secondary system piping in nuclear power plants (NPPs). All NPPs have their management programs to ensure pipe integrity from wall-thinning. This study analyzed the pipe wall-thinning caused by changing the amine, which is used for adjusting the water chemistry in the secondary system of NPPs. The pH change was analyzed according to the addition of amine. Then, the wear rate calculated in two different amines was compared at the steam cycle in NPPs. As a result, increasing the pH at operating temperature (Hot pH) can reduce the rate of FAC damage significantly. Wall-thinning is affected by amine characteristics depending on temperature and quality of water.

Cause Analysis of Flow Accelerated Corrosion and Erosion-Corrosion Cases in Korea Nuclear Power Plants

  • Lee, Y.S.;Lee, S.H.;Hwang, K.M.
    • Corrosion Science and Technology
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    • v.15 no.4
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    • pp.182-188
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    • 2016
  • Significant piping wall thinning caused by Flow-Accelerated Corrosion (FAC) and Erosion-Corrosion (EC) continues to occur, even after the Mihama Power Station unit 3 secondary pipe rupture in 2004, in which workers were seriously injured or died. Nuclear power plants in many countries have experienced FAC and EC-related cases in steam cycle piping systems. Korea has also experienced piping wall thinning cases including thinning in the downstream straight pipe of a check valve in a feedwater pump line, the downstream elbow of a control valve in a feedwater flow control line, and failure of the straight pipe downstream of an orifice in an auxiliary steam return line. Cause analyses were performed by reviewing thickness data using Ultrasonic Techniques (UT) and, Scanning Electron Microscope (SEM) images for the failed pipe, and numerical simulation results for FAC and EC cases in Korea Nuclear Power Plants. It was concluded that the main cause of wall thinning for the downstream pipe of a check valve is FAC caused by water vortex flow due to the internal flow shape of a check valve, the main cause of wall thinning for the downstream elbow of a control valve is FAC caused by a thickness difference with the upstream pipe, and the main cause of wall thinning for the downstream pipe of an orifice is FAC and EC caused by liquid droplets and vortex flow. In order to investigate more cases, additional analyses were performed with the review of a lot of thickness data for inspected pipes. The results showed that pipe wall thinning was also affected by the operating condition of upstream equipment. Management of FAC and EC based on these cases will focus on the downstream piping of abnormal or unusual operated equipment.