Technical Basis for Application of Collapse Moments for Locally Thinned Pipes Subjected to Torsion and Bending Proposed for ASME Section XI

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Kunio Hasegawa ◽  
Yinsheng Li ◽  
Bostjan Bezensek ◽  
Phuong H. Hoang ◽  
Howard J. Rathbun
Keyword(s):  
Power Plants ◽  
Plastic Collapse ◽  
Bending Moments ◽  
Pure Bending ◽  
Plastic Bending ◽  
Evaluation Procedures ◽  
Wall Thinning ◽  
Applicable Range ◽  
Technical Basis ◽  
Local Wall Thinning

Piping components in power plants may experience combined bending and torsion moments during operation. There is a lack of guidance for pipe evaluation for pipes with local wall-thinning flaws under the combined bending and torsion moments. ASME boiler and pressure vessel (B&PV) Code Section XI Working Group is currently developing fully plastic bending pipe evaluation procedures for pressurized piping components containing local wall thinning subjected to combined torsion and bending moments. Using elastic fully plastic finite element (FE) analyses, plastic collapse bending moments under torsions were obtained for 4 (114.3)–24 (609.6) in. (mm) diameter pipes with various local wall-thinning flaw sizes. The objective of this paper is to introduce an equivalent moment, which combines torsion and bending moments by a vector summation, and to establish the applicable range of wall-thinning lengths, angles, and depths, where the equivalent moments are equal to pure bending collapse moments.

Technical Basis for Application of Collapse Moments for Locally Thinned Pipes Subjected to Torsion and Bending Proposed for ASME Section XI

2014 ◽  
Author(s):  
Kunio Hasegawa ◽  
Yinsheng Li ◽  
Bostjan Bezensek ◽  
Phuong H. Hoang ◽  
Howard J. Rathbun
Keyword(s):  
Power Plants ◽  
Bending Moments ◽  
Finite Element Analyses ◽  
Pure Bending ◽  
Plastic Bending ◽  
Evaluation Procedures ◽  
Wall Thinning ◽  
Applicable Range ◽  
Technical Basis ◽  
Local Wall Thinning

Piping components in power plants may experience combined bending and torsion moments during operation. There is a lack of guidance for pipe evaluation for pipes with local wall thinning flaws under the combined bending and torsion moments. ASME B&PV Code Section XI Working Group is currently developing fully plastic bending pipe evaluation procedures for pressurized piping components containing local wall thinning subjected to combined torsion and bending moments. Using elastic fully plastic finite element analyses, plastic collapse bending moments under torsions were obtained for 4 (114.3) to 24 (609.6) inch (mm) diameter pipes with various local wall thinning flaw sizes. The objective of this paper is to introduce an equivalent moment, which combines torsion and bending moments by a vector summation, and to establish the applicable range of wall thinning lengths, angles and depths, where the equivalent moments are equal to pure bending moments.

Evaluation of Torsion and Bending Collapse Moments for Pipes With Local Wall Thinning

2011 ◽  
Author(s):  
Kunio Hasegawa ◽  
Yinsheng Li ◽  
Bostjan Bezensek ◽  
Phuong Hoang
Keyword(s):  
Power Plants ◽  
Bending Moment ◽  
Combined Loading ◽  
Bending Moments ◽  
Pure Bending ◽  
Evaluation Procedures ◽  
Wall Thinning ◽  
Loading Modes ◽  
Bending Fracture ◽  
Local Wall Thinning

ASME B&PV Code Section XI provides fully plastic bending fracture evaluation procedures for pressurized piping components containing flaws subjected to bending and membrane loads. The piping components in power plants may experience only bending moments but also occasionally small torsion moments, simultaneously. Currently, there is a lack of guidance in the Section XI for combined loading modes including torsion. Finite element analyses were conducted in this paper for 24-inch diameter straight pipes with local wall thinning. The pipe was subject to combined bending and torsion moments. It is shown that the effect of torsion moment on plastic collapse bending moment for the pipes depends on the local wall thinning sizes. In addition, it is found that the equivalent moments defined as the root of the sum of the squares (RSS) of the torsion and bending moments is equal to pure bending moments, when wall thinning depth is shallow.

Effect of Torsion on Collapse Bending Moment for 24-Inch Diameter Schedule 80 Pipes With Wall Thinning

2012 ◽  
Author(s):  
Kunio Hasegawa ◽  
Yinsheng Li ◽  
Bostjan Bezensek ◽  
Phuong Hoang
Keyword(s):  
Power Plants ◽  
Bending Moment ◽  
Combined Loading ◽  
Bending Moments ◽  
Compressive Stresses ◽  
Wall Thinning ◽  
Nominal Thickness ◽  
Calculation Results ◽  
Loading Modes ◽  
Local Wall Thinning

Piping items in power plants may experience combined bending and torsion moments during operation. Currently, there is a lack of guidance in the ASME B&PV Code Section XI for combined loading modes including pressure, torsion and bending. Finite element analyses were conducted for 24-inch diameter Schedule 80 pipes with local wall thinning subjected to tensile and compressive stresses. Plastic collapse bending moments were calculated under constant torsion moments. From the calculation results, it can be seen that collapse bending moment for pipes with local thinning subjected to tensile stress is smaller than that subjected to compressive stress. In addition, equivalent moment is defined as the root the sum of the squares of the torsion and bending moments. It is found that the equivalent moments can be approximated with the pure bending moments, when the wall thinning length is equal or less than 7.73R·t for the wall thinning depth of 75% of the nominal thickness, where R is the mean radius and t is the wall thickness of the pipe.

Inclusion of Torsion With Bending and Pressure Loads for Pipes With Thin-Wall Regions

2011 ◽  
Author(s):  
Bostjan Bezensek ◽  
Yinsheng Li ◽  
Kunio Hasegawa ◽  
Phuong H. Hoang
Keyword(s):  
Pipe Wall ◽  
Plastic Collapse ◽  
Thin Wall ◽  
Finite Element Analyses ◽  
Pure Bending ◽  
Pipe Wall Thickness ◽  
Wall Thinning ◽  
Equivalent Load ◽  
Bending Loading ◽  
Local Wall Thinning

Piping installations may experience local wall thinning under predominant pressure and bending loading with a small amount of torsion loading. Assessment of the remaining pipe integrity must account for all loads and can benefit from resolving the multiaxial loads into an equivalent load. This paper presents results of the finite element analyses of straight pipes containing non-planar flaws (i.e. local wall thinning areas) subject to combination of pressure, bending and torsion. The pressure is 8 MPa and the torsion stresses are limited to 20% of the material’s flow stress. Flaws are introduced into a 4 inch OD pipe with an R/t of 6.64 and 9.36. The incipient plastic collapse moment at a given torsion moment is determined and compared with the plastic collapse moment of the pure bending case. The results show that for flaws with a depth less than 60% of the nominal pipe wall thickness the bending and torsion moments can be combined into an equivalent moment by vector summation (the Root of the Sum of Squares approach). For deeper flaws the effect of pipe and flaw geometry is observed.

Application of Laser-Generated Ultrasound for Evaluation of Thickness Reduction in Carbon Steel Pipes

2006 ◽  
Vol 321-323 ◽  
pp. 743-746 ◽  
Author(s):  
Jong Ho Park ◽  
Joon Hyun Lee ◽  
Gyeong Chul Seo ◽  
Sang Woo Choi
Keyword(s):  
Carbon Steel ◽  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Power Plants ◽  
Guided Wave ◽  
Thickness Reduction ◽  
Steel Pipes ◽  
Time Frequency ◽  
Wall Thinning ◽  
Local Wall Thinning

In carbon steel pipes of nuclear power plants, local wall thinning may result from erosion-corrosion or flow-accelerated corrosion(FAC) damage. Local wall thinning is one of the major causes for the structural fracture of these pipes. Therefore, assessment of local wall thinning due to corrosion is an important issue in nondestructive evaluation for the integrity of nuclear power plants. In this study, laser-generated ultrasound technique was employed to evaluate local wall thinning due to corrosion. Guided waves were generated in the thermoelastic regime using a Q-switched pulsed Nd:YAG laser with a linear slit array. . In this paper, time-frequency analysis of ultrasonic waveforms using wavelet transform allowed the identification of generated guided wave modes by comparison with the theoretical dispersion curves. Modes conversion and group velocity were employed to detect thickness reduction.

Development of Engineering Formulae for Stress Concentration Factors of Local Wall Thinning in CANDU Feeder Pipe Under Pressure

2011 ◽  
Author(s):  
Jong Sung Kim ◽  
Jae Seok Seo
Keyword(s):  
Stress Concentration ◽  
Power Plants ◽  
Degradation Mechanism ◽  
Peak Stress ◽  
Design Stage ◽  
Fatigue Assessment ◽  
Wall Thinning ◽  
Concentration Factors ◽  
Stress Concentration Factors ◽  
Local Wall Thinning

Feeder pipes that connect the inlet and outlet headers with the in-reactor fuel channels in CANDU nuclear power plants are considered as safety Class 1 piping items. Therefore, fatigue of the feeder pipes should be assessed at design stage in order to verify structural integrity during design lifetime. In accordance with the fatigue assessment result, cumulative usage factors of some feeder pipes have significant values. An active degradation mechanism for the outlet feeder piping made of SA-106 Grade B carbon steel is local wall thinning due to flow-accelerated corrosion. This local wall thinning can cause increase of peak stress due to stress concentration by notch effect. The increase of peak stress results in increase of the cumulative usage factor. However, present fatigue assessment doesn’t consider the stress concentration due to the local wall thinning. Therefore, it is necessary to assess the effect of local wall thinning on the stress concentration. This study developed the engineering formulae for stress concentration factors of the local wall thinning in the CANDU feeder pipe under internal pressure by using the engineering procedure of Kinectrics Co.. Finally, the developed formulae were applied to the elbow feeder pipes and compared with the finite element analysis results. As a result of comparison, it is identified that the engineering formulae is valid.

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.

Assessment of Piping Field Failures and Burst Tests on Carbon Steel Pipes With Local Wall Thinning Using ASME Section XI Code Case N-597-2

2009 ◽  
Author(s):  
Kunio Hasegawa ◽  
Toshiyuki Meshii ◽  
Douglas A. Scarth
Keyword(s):  
Carbon Steel ◽  
Accelerated Corrosion ◽  
Steel Pipes ◽  
Pipe Burst ◽  
Evaluation Procedures ◽  
Wall Thinning ◽  
American Society ◽  
Corrosion Mechanisms ◽  
Flow Accelerated Corrosion ◽  
Local Wall Thinning

One of the more common modes of degradation in power plant piping has been wall thinning due to erosion-corrosion or flow-accelerated corrosion. Extensive work has been performed to understand flow-accelerated corrosion mechanisms and develop fracture criteria of locally thinned pipes, since the tragic events at Surry Unit 2 and Mihama Unit 3. A large number of tests have been performed on carbon steel pipes, elbows and tees with local wall thinning. In addition, the American Society of Mechanical Engineers Boiler and Pressure Vessel Code provides procedures in Code Case N-597-2 for evaluation of wall thinning in pipes. This paper provides validation of the evaluation procedures in Code Case N-597-2 by comparing with the field rupture data and pipe burst test data. The allowable wall thinning from the Code Case N-597-2 procedures is shown to maintain adequate margins against rupture.

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.

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