Reference Stress Based Approach to Predict Failure Strength of Pipes With Local Wall Thinning Under Single Loading

2004 ◽  
Vol 126 (2) ◽  
pp. 194-201 ◽  
Author(s):  
Yun-Jae Kim ◽  
Do-Jun Shim ◽  
Hwan Lim ◽  
Young-Jin Kim
Keyword(s):  
Equivalent Stress ◽  
Three Dimensional ◽  
Failure Strength ◽  
Creep Stress ◽  
Estimation Equations ◽  
Reference Stress ◽  
Wall Thinning ◽  
Approximate Estimation ◽  
Failure Loads ◽  
Local Wall Thinning

This paper proposes a new method to estimate failure strength of a pipe with local wall thinning. The method is based on the equivalent stress averaged over the minimum ligament in the locally wall thinned region. The highlight of the proposed method is to propose a simple scheme to estimate the equivalent stress in the minimum ligament. Inspired by the reference stress method for approximate creep stress analysis, approximate estimation equations are proposed for the equivalent stress in the minimum ligament, which are then calibrated using detailed elastic-plastic three-dimensional FE analysis. Remarkably the resulting estimation equations are found to be insensitive not only to pipe and defect geometries but also to material. Comparison of failure loads, predicted according to the proposed method, with published test data for corroded pipes shows excellent agreement, which provides confidence in the use of the proposed method to assess local wall thinning in pipes. Furthermore, the proposed method is conceptually simple and thus easy to be extended to more complex situations.

Reference Stress Approach for Failure Strength Estimates of a Pipe With Local Wall Thinning

2005 ◽  
Author(s):  
Yun-Jae Kim ◽  
Young-Jin Kim
Keyword(s):  
Equivalent Stress ◽  
Fe Analysis ◽  
Creep Stress ◽  
Estimation Equations ◽  
Reference Stress ◽  
Wall Thinning ◽  
Approximate Estimation ◽  
Failure Loads ◽  
Reference Stress Approach ◽  
Local Wall Thinning

This paper proposes a method based on the reference stress a approach to estimate residual strength of a pipe with local wall thinning. The method is based on the equivalent stress averaged over the minimum ligament in the locally wall thinned region. Inspired by the reference stress method for approximate creep stress analysis, approximate estimation equations for the equivalent stress in the minimum ligament are proposed, which are then calibrated using detailed elastic-plastic 3-D FE analysis. The resulting estimation equations are found to be insensitive not only to pipe and defect geometries but also to material. Comparison of failure loads, predicted according to the proposed method, with published test data for corroded pipes shows excellent agreement.

Reference Stress Based Approach to Predict Failure Strength of Pipes With Local Wall Thinning Under Combined Loading

2005 ◽  
Vol 127 (1) ◽  
pp. 76-83 ◽  
Author(s):  
Do-Jun Shim ◽  
Young-Jin Kim ◽  
Yun-Jae Kim
Keyword(s):  
Internal Pressure ◽  
Equivalent Stress ◽  
New Method ◽  
Combined Loading ◽  
Failure Strength ◽  
Creep Stress ◽  
Reference Stress ◽  
Wall Thinning ◽  
Good Agreement ◽  
Local Wall Thinning

In the previous work carried out by the authors, a new method to estimate failure strength of a pipe with local wall thinning subject to either internal pressure or global bending has been proposed. The proposed method was based on the equivalent stress averaged over the minimum ligament in the locally wall thinned region, and the simple scheme to estimate the equivalent stress in the minimum ligament was proposed, based on the reference stress concept for creep stress analysis. This paper extends the new method to combined internal pressure and global bending. The proposed method is validated against FE results for various geometries of local wall thinning under combined loading. The effect of internal pressure is also investigated in the present study. Comparison of maximum moments, predicted according to the proposed method, with published full-scale pipe test data for locally wall thinned pipes under combined internal pressure and global bending, shows good agreement.

Effect of Circumferential Location of Local Wall Thinning Defect on the Collapse Moment of Elbow

2006 ◽  
Author(s):  
Jin Weon Kim ◽  
Yeon Soo Na ◽  
Chi Yong Park
Keyword(s):  
Carbon Steel ◽  
Internal Pressure ◽  
Nuclear Power ◽  
Three Dimensional ◽  
Piping System ◽  
Main Concern ◽  
Wall Thinning ◽  
Bending Load ◽  
Local Wall Thinning ◽  
Steel Piping

Local wall-thinning due to flow-accelerated corrosion is one of the degradation mechanisms of carbon steel piping in nuclear power plant (NPP). It is a main concern in carbon steel piping systems in terms of the safety and operability of the NPP. Recently, the integrity of piping components containing local wall-thinning has become more important for maintaining the reliability of a nuclear piping system, and has been the subject of several studies. However, although wall-thinning in pipe bends and elbows has been frequently reported, its effect on the integrity of pipe bends and elbows has not yet been systematically investigated. Thus, the purpose of this study was to investigate the effect of the circumferential location of a local wall-thinning defect on the collapse behavior of an elbow. For this purpose, the present study used three-dimensional finite element analyses on a 90-degree elbow containing local wall-thinning at the crown of the bend region and evaluated the collapse moment of the wall-thinned elbow under various thinning geometries and loading conditions. The combined internal pressure and bending loads were considered as an applied load. Internal pressure of 0∼20 MPa and both closing-and opening-mode bending were applied. The results of the analyses showed that a reduction in the collapse moment of the elbow due to local wall-thinning was more significant when a defect was located at the crown than when a defect was located at the intrados and extrados. Also, the effect of the internal pressure on the collapse moment depended on the circumferential location of the thinning defect and mode of the bending load.

Failure Behavior of Carbon Steel Pipe Having Local Wall Thinning Near Tee Joint

2006 ◽  
Author(s):  
Kotoji Ando ◽  
Koji Takahashi ◽  
Masakazu Hisatsune ◽  
Kunio Hasegawa
Keyword(s):  
Finite Element Method ◽  
Three Dimensional ◽  
Metal Loss ◽  
Failure Behavior ◽  
Fracture Type ◽  
Bending Tests ◽  
Four Point Bending ◽  
Wall Thinning ◽  
Erosion Corrosion ◽  
Local Wall Thinning

Monotonic four-point bending tests were conducted using tee pipe specimens having local wall thinning. The effects of local wall thinning on the failure behaviors of tee pipes were investigated. Local wall thinning was machined on the inside of pipes in order to simulate erosion/corrosion metal loss. The configurations of the eroded area were l = 100 mm in eroded axial length, d/t = 0.5 and 0.8 in eroded ratio, and 2θ = 90° and 180° in eroded angle. The area undergoing local wall thinning was subjected to tensile stress. It was found that fracture type could be classified into ovalization or crack initiation, depending on eroded ratio. Three-dimensional elasto-plastic analyses were also carried out using finite element method to discuss the effects of position and geometries of wall thinning in both tee pipes and straight pipes.

Fracture and Deformation Behaviors of Tee Pipe With Local Wall Thinning Under Monotonic Bending

2004 ◽  
Author(s):  
Koji Takahashi ◽  
Kotoji Ando ◽  
Masakazu Hisatsune ◽  
Kunio Hasegawa
Keyword(s):  
Three Dimensional ◽  
Local Buckling ◽  
Metal Loss ◽  
The Finite Element Method ◽  
Bending Tests ◽  
Four Point Bending ◽  
Wall Thinning ◽  
Fracture Behaviors ◽  
Deformation Behaviors ◽  
Local Wall Thinning

Monotonic four-point bending tests were conducted using tee pipe specimens having local wall thinning. The effects of local wall thinning on the fracture behaviors of tee pipes were investigated. Local wall thinning was machined on the inside of pipes in order to simulate erosion/corrosion metal loss. The configurations of the eroded area were l = 100 mm in eroded axial length, d/t = 0.5 and 0.8 in eroded ratio, and 2θ = 90° in eroded angle. The area undergoing local wall thinning was subjected to either tensile or compressive stress. Fracture behaviors of the tee pipes were compared with those of straight pipes. It was found that fracture type could be classified into ovalization, local buckling, and crack initiation, depending on pipe shape, eroded ratio, and stress at the eroded area. Three-dimensional elasto-plastic analyses were also carried out using the finite element method, which is able to accurately simulate fracture behaviors.

Creep Stress Analyses Affected by Defect Geometries on P91 Pipe With Local Wall Thinning Under High Temperature

2010 ◽  
Author(s):  
Jilin Xue ◽  
Changyu Zhou ◽  
Jian Peng
Keyword(s):  
High Temperature ◽  
Creep Strain ◽  
Power Plants ◽  
Creep Condition ◽  
Service Condition ◽  
Stress And Strain ◽  
Steel Pipes ◽  
Creep Stress ◽  
Wall Thinning ◽  
Local Wall Thinning

P91 heat-resistant steel pipes are widely used at high temperature in power plants and nuclear power plants. The service condition and manufacturing process may produce defects of local wall thinning, which may result in stress redistribution of the pipes during the service process at elevated temperature. For the purpose of understanding the creep stress and strain accumulation affected by local wall thinning geometries under creep condition, three groups of models were calculated, using three-dimensional models based on finite element analyses (FEA) codes ABAQUS. In this study, monotonic internal pressure was conducted on P91 full-scale steel pipes at 625°C, with local wall thinning located at the inner surface. Then, the creep strain and stress of pipes after 100,000h could be obtained corresponding to different models. Based on the analysis, the figures of creep stress and strain varying with defect geometries were plotted. Then, the stress and strain of pipes with local wall thinning affected by defect geometries, including different defect depths, different defect axial lengths and different defect hoop angles, were discussed. The results indicate that creep stress and creep strain increase with defect geometries. The variation laws have been summarized. The research results can provide the possibility on safety assessment and structure integrity analysis of the pipe with local wall thinning at high temperature effectively.

Finite Element Based Plastic Loads for Elbows With Local Wall Thinning

2007 ◽  
Author(s):  
Jong-Hyun Kim ◽  
Chang-Sik Oh ◽  
Joon-Hyuk Ahn ◽  
Yun-Jae Kim ◽  
Chi-Yong Park ◽  
...  
Keyword(s):  
Finite Element ◽  
Large Strain ◽  
Three Dimensional ◽  
Geometry Effect ◽  
Perfectly Plastic ◽  
Wall Thinning ◽  
Plastic Materials ◽  
Wide Range ◽  
Elastic Perfectly Plastic ◽  
Local Wall Thinning

Based on systematic three-dimensional (3-D), large strain FE limit analyses using elastic-perfectly plastic materials, this paper quantifies the effect of local wall thinning on plastic behaviors and TES (twice-elastic-slope) plastic loads for 90° elbows under in-plane bending. The thinning geometry is assumed to be rectangular rather than circular, but the nonlinear geometry effect is fully considered. Results from systematic analyses lead to simple approximations for TES plastic loads, covering a wide range of elbow and thinning geometries.

Creep Stress Analyses Affected by Load Properties on P91 Pipe with Local Wall Thinning under High Temperature

2011 ◽  
Vol 704-705 ◽  
pp. 1304-1309
Author(s):  
Ji Lin Xue ◽  
Chang Yu Zhou ◽  
Jian Peng
Keyword(s):  
High Temperature ◽  
Internal Pressure ◽  
Creep Strain ◽  
Power Plants ◽  
Creep Condition ◽  
Stress Redistribution ◽  
Stress And Strain ◽  
Creep Stress ◽  
Wall Thinning ◽  
Local Wall Thinning

The local wall thinning defect is very normal on pipes in power plants, which may result in stress redistribution of the pipes during the service process at elevated temperature. For the purpose of understanding the stress redistribution and strain accumulation of pipes with local wall thinning affected by load properties under creep condition, three groups of models were calculated, using three-dimensional elastic-plastic finite element analyses (FEA) based on FEA codes ABAQUS. In this study, the pipes has an identical defect of local wall thinning, the load properties and values are changed. Three groups of load properties, considering here, were monotonic internal pressure, monotonic moment and both internal pressure and moment, respectively. The numerical simulation conducted on P91 full-scale steel pipes at 625°C, with local wall thinning located at the inner surface. Then, von Mises stress and creep strain of pipes after 100,000h could be obtained corresponding to different models. Based on the analysis, the figures of creep stress and strain varying with load properties were plotted. Then, the stress and strain of pipes with local wall thinning affected by load properties were discussed. The results indicate that creep stress and creep strain increase with load properties. The variation laws have been summarized. The research results can provide the possibility on safety assessment and structure integrity analysis of the pipe with local wall thinning at high temperature effectively.

Failure Behavior of Pipe Having Local Wall Thinning in Downstream Region of Orifice

2005 ◽  
Author(s):  
Koji Takahashi ◽  
Kotoji Ando ◽  
Masakazu Hisatsune ◽  
Kunio Hasegawa
Keyword(s):  
Crack Initiation ◽  
Three Dimensional ◽  
Local Buckling ◽  
Metal Loss ◽  
Failure Behavior ◽  
Initiation Point ◽  
Four Point Bending ◽  
Wall Thinning ◽  
Fracture Behaviors ◽  
Local Wall Thinning

Monotonic four-point bending tests were conducted using pipe specimens having orifice undergoing local wall thinning. The effects of local wall thinning on the fracture behaviors of pipe were investigated. Local wall thinning was machined on the inside of pipes in order to simulate erosion/corrosion metal loss. The configurations of the eroded area were l = 100 mm in eroded axial length, d/t = 0.5 and 0.8 in eroded ratio, and 2θ = 180° in eroded angle. The area undergoing local wall thinning was subjected to either tensile or compressive stress. Failure type could be classified into ovalization, local buckling, and crack initiation, depending on eroded ratio, and stress at the eroded area. Three-dimensional elasto-plastic analyses were also carried out using the finite element method, which is able to accurately simulate fracture behaviors. The crack initiation point could be successfully predicted by the criterion proposed by Miyazaki et al..

Effect of Local Wall Thinning on Maximum Load Carrying Capacities of Elbows under Bending

2007 ◽  
Vol 345-346 ◽  
pp. 517-520
Author(s):  
Jong Hyun Kim ◽  
Joong Hyuk Ahn ◽  
Seok Pyo Hong ◽  
Yun Jae Kim ◽  
Chi Yong Park
Keyword(s):  
Three Dimensional ◽  
Limit Load ◽  
Maximum Load ◽  
Small Strain ◽  
Perfectly Plastic ◽  
Wall Thinning ◽  
Plastic Materials ◽  
Load Carrying ◽  
Elastic Perfectly Plastic ◽  
Local Wall Thinning

This paper provides closed-form plastic limit load solutions for elbows with local wall thinning under in-plane bending, via three-dimensional (3-D), small strain FE limit analyses using elastic-perfectly plastic materials. Wide ranges of elbow and thinning geometries are considered.

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