Plastic Collapse Stresses for Pipes With Inner and Outer Circumferential Cracks

2019 ◽  
Vol 141 (2) ◽  
Author(s):  
Vratislav Mares ◽  
Kunio Hasegawa ◽  
Yinsheng Li ◽  
Valery Lacroix
Keyword(s):  
Outer Surface ◽  
Bending Moment ◽  
Thick Wall ◽  
Plastic Collapse ◽  
Surface Cracks ◽  
Bending Stress ◽  
Moment Equations ◽  
Bending Stresses ◽  
Crack Angle ◽  
Uncracked Ligament

Bending stresses at incipient plastic collapse for pipes with circumferential surface cracks are predicted by net-section stress approach. Appendix C-5320 of ASME B&PV Code Section XI provides an equation of bending stress at the plastic collapse, where the equation is applicable for both inner and outer surface cracks. That is, the collapse stresses for pipes with inner and outer surface cracks are the same, because of the pipe mean radius at the cracked section being entirely the same. Authors considered the separated pipe mean radii at the cracked ligament and at the uncracked ligament. Based on the balances of axial force and bending moment, equations of plastic collapse stresses for both inner and outer cracked pipes were developed. It is found that, when the crack angle and depth are the same, the collapse stress for inner cracked pipe is slightly higher than that calculated by the Appendix C equation, and the collapse stress for outer cracked pipe is slightly lower than that by the Appendix C equation, as can be expected. The collapse stresses derived from the three equations are almost the same in most instances. However, for less common case where the crack angle and depth are very large for thick wall pipes, the differences among the three collapse stresses become large. Code users pay attention to the margins of plastic collapse stresses for outer cracked pipes, when using Appendix C equation.

Prediction for Plastic Collapse Stresses for Pipes With Inner and Outer Circumferential Flaws

2018 ◽  
Author(s):  
Kunio Hasegawa ◽  
Yinsheng Li ◽  
Vratislav Mares ◽  
Valery Lacroix
Keyword(s):  
Axial Force ◽  
Outer Surface ◽  
Bending Moment ◽  
Thick Wall ◽  
Plastic Collapse ◽  
Bending Stress ◽  
Surface Flaws ◽  
Bending Stresses

Bending stresses at incipient plastic collapse for pipes with circumferential surface flaws are predicted by net-section stress approach. Appendix C-5320 of ASME B&PV Code Section XI provides a formula of bending stress at the plastic collapse, where the formula is applicable for both inner and outer surface flaws. That is, the collapse stresses for pipes with inner and outer surface flaws are the same, because of the pipe mean radius at the flawed section being entirely the same. Authors considered the separated pipe mean radii at the flawed ligament and at the un-flawed ligament. Based on the balances of axial force and bending moment, formulas of plastic collapse stresses for each inner and outer flawed pipe were obtained. It is found that, when the flaw angle and depth are the same, the collapse stress for inner flawed pipe is slightly higher than that calculated by Appendix C-5320 formula, and the collapse stress for outer flawed pipe is slightly lower than that by Appendix C-5320 formula, as can be expected. The collapse stresses derived from the three formulas are almost the same in most instances. For less common case where the flaw angle and depth are very large for thick wall pipes, the differences amongst the three collapse stresses become large.

Fuzzy Heuristic Gradient Projection for Frame Topology Optimization

2005 ◽  
Author(s):  
Mohamed S. Senousy ◽  
Hesham A. Hegazi ◽  
Sayed M. Metwalli
Keyword(s):  
Fuzzy Logic ◽  
Fuzzy Logic Controller ◽  
Axial Stress ◽  
Equivalent Stress ◽  
Optimal Solution ◽  
Bending Moment ◽  
Gradient Projection ◽  
Bending Stress ◽  
Allowable Stress ◽  
Bending Stresses

In this paper, a new methodology to obtain an optimal structure size considering geometries nonlinearity is presented. This method makes use of Heuristic Gradient Projection method in addition to Fuzzy Logic. The Heuristic Gradient Projection (HGP) method, a previously developed method for 3D-frame design and optimization, utilizes mainly bending stress relations in order to simplify the process of iterations. HGP is based on comparing the resulting equivalent stress with the allowable stress value. The proposed Fuzzy Heuristic Gradient Projection (FHGP) approach incorporates both bending stress and axial stress when processing with the allowable stress value. The weighting factors of both axial and bending stresses are found using a Fuzzy Logic controller. Fuzzy logic is incorporated to reach an optimal solution with lesser number of function evaluations. A simple cantilever example, subjected to axial force and bending moment, is presented to illustrate this approach in addition to a 10-member planar frame that is used to prove the efficacy of the new method. FHGP approach generally results in faster convergence.

An Investigation of Drawbead Models for Springback Prediction

2006 ◽  
Author(s):  
F. Ren ◽  
Z. C. Xia
Keyword(s):  
Computational Efficiency ◽  
Force Control ◽  
Bending Moment ◽  
Bending Stress ◽  
Displacement Control ◽  
The Real ◽  
Part Geometry ◽  
Significant Challenge ◽  
Bending Stresses ◽  
Springback Prediction

Accurate prediction of springback for rail-type structures remains a significant challenge for automotive stamping. A major characteristic of forming such parts is that metals go through drawbeads and die-entry radii and often end up within part geometry (i.e., inside trimline). The bending-unbending stresses generated by drawbeads contribute significantly to the eventual springback. In production springback simulation, line drawbead models are generally used to represent the restraining forces provided by the real drawbeads for computational efficiency. While such models can be well correlated to match overall deformation of the part, the bending stresses could not be accurately captured. In the present study, a model of an aluminum U-channel is used to evaluate springback predictability of line drawbead model, which is then compared against simulations that employ detailed drawbead geometry. The results show that the line drawbead model largely under-predicts the springback and the bending moment. The accuracy of the prediction cannot be improved through different binder simulation strategies such as displacement-control or force-control. The study suggests that either real drawbeads be modeled, or the bending stress be incorporated into the line model to improve springback prediction.

Improvement and Assessment of the Plastic Collapse Bending Moment Equations in Circumferentially Cracked Pipe

2021 ◽  
Author(s):  
Cécilia Desclaux ◽  
Valéry Lacroix ◽  
Kunio Hasegawa
Keyword(s):  
Bending Moment ◽  
Moment Equation ◽  
Neutral Axis ◽  
Plastic Collapse ◽  
Moment Equations ◽  
Equilibrium Equations ◽  
Extended Finite Element ◽  
Pipe Section ◽  
Axis Position ◽  
Method Analysis

Abstract The plastic collapse bending moment in a pipe cross-section with a circumferential crack is defined in ASME B&PV Code Section XI, Appendix C using simplified equilibrium equations by approximating the pipe mean radius Rm and the neutral axis angle β. In previous papers it was demonstrated by the authors that, for externally cracked pipes, those simplified equilibrium equations are not conservative and hence improved equations were developed and proposed which account for the cracked pipe ligament mean radius Rmc. In this paper, it is demonstrated that the accuracy of the collapse bending moment equation can be refined by taking into account the neutral axis position Yna of the cracked pipe section. This leads to exact collapse bending moment equations without any approximation on the pipe mean radius Rm nor on the neutral axis angle β. In this framework, it is shown that, for externally cracked pipes, the Appendix C equations could lead to more than 20% less conservative collapse bending moment than with the exact equations. An extended finite element method analysis completes this study to assess the relevance of the model used to determine the plastic collapse bending moment.

Plastic collapse moment equations of throughwall axially cracked elbows subjected to in-plane bending moment

2008 ◽  
Vol 75 (8) ◽  
pp. 2260-2275 ◽  
Author(s):  
J. Chattopadhyay ◽  
W. Venkatramana ◽  
B.K. Dutta ◽  
H.S. Kushwaha
Keyword(s):  
Bending Moment ◽  
Plastic Collapse ◽  
Moment Equations ◽  
Plane Bending

The Limit Load Calculations for Pipe Bend With Axial Part-Through Defect

2010 ◽  
Author(s):  
I. V. Orynyak ◽  
I. V. Lokhman ◽  
S. O. Okhrimchuk
Keyword(s):  
Bending Moment ◽  
Limit Load ◽  
Strength Reduction ◽  
Simultaneous Action ◽  
Bending Stress ◽  
Pipe Bend ◽  
Inner Pressure ◽  
Axial Part ◽  
Load Calculation ◽  
Bending Stresses

Pipe bend is very complicated element for the structural integrity assessment. Up to day there is no conventionally adopted technique for limit load calculation of pipe bend even without any defect. The problem is that at application of outer bending moment the pipe bend cross section ovalizes and the process of deformation can be described only with accounting for the geometrical nonlinearity. The paper deal with limit load calculation for pipe bend with axial part-through defect for particular case when circumferential stresses originated both from inner pressure and outer bending moment dominate over axial stresses from the moment and axial force. Two extreme cases are considered at start. First one is the action of the inner pressure only. The “Institute for Problems of Strength limit load model” (IPS model) can be applied here without any restrictions. The second case is consideration of circumferential bending stresses which have appeared due to ovalization from the outer bending moment. The model of the transmission of stresses from the defected region to the undamaged regions is suggested and the resulting formula for the stress concentration (or strength reduction) coefficient is obtained. At last the simultaneous action of both loadings is considered. As result the analytical formula for the reference stress calculation which is similar in appearance to that of API 579 for accounting for membrane stress as well as bending stress is suggested. The only difference is that strength reduction coefficients are considered for both the membrane stresses from inner pressure and bending stress from ovalization. This differs from API 579 approach where the influence of the defects length on the bending stresses is not taken into account.

Plastic Collapse Stresses for Thick Wall Pipes With External Cracks

2019 ◽  
Author(s):  
Kunio Hasegawa ◽  
Yinsheng Li ◽  
Valery Lacroix ◽  
Vratislav Mares
Keyword(s):  
Pipe Wall ◽  
Internal Surface ◽  
Limit Load ◽  
Thick Wall ◽  
Plastic Collapse ◽  
Surface Cracks ◽  
Pipe Wall Thickness ◽  
Asme Code ◽  
Bending Capacity ◽  
New Equation

Abstract Bending stress at plastic collapse for a circumferentially cracked pipe is predicted by limit load equation provided by the Appendix C of the ASME Code Section XI. The equation of the Appendix C is applicable for pipes with both external and internal surface cracks. On the other hand, the authors have developed an equation taking into account the pipe mean radii at non-cracked area and at cracked ligament area. From the comparison of Appendix C equation and the new equation, the plastic collapse stress estimated by the Appendix C equation gives 20 to 30% less conservative bending capacity prediction for external cracked pipes with small Rm/t, where Rm is the pipe mean radius and t is the pipe wall thickness. This paper discusses the limitation of the use of Rm/t for the Appendix C equation.

Development of the mathematical model for assessing the optimal measurement step when surveying the depth of the underground pipeline from the ground

2020 ◽  
Vol 10 (4) ◽  
pp. 364-371
Author(s):  
Ruslan V. Aginey ◽  
◽  
Rustem R. Islamov ◽  
Alexey A. Firstov ◽  
Elmira A. Mamedova ◽  
...  
Keyword(s):  
Mathematical Models ◽  
Survey Data ◽  
Ground Surface ◽  
Maximum Error ◽  
Large Error ◽  
Bending Stress ◽  
Buried Pipeline ◽  
Optimal Measurement ◽  
Pipeline Section ◽  
Bending Stresses

Existing methods for estimating the bending stresses of buried pipeline section based on the survey data for the depth of the axis of the pipeline from the ground surface are characterized by a large error between the real values of the bending stress and the values of the bending stress obtained from the calculation results based on the survey data. The purpose of this study is to improve the methodology for calculating the bending stresses of buried pipeline section based on the results of determining the depth of the axis of the pipeline from the ground surface, taking into account the design features of the pipeline and the used search equipment. Mathematical models are proposed that allow for the set value of the maximum error in determining bending stresses for a particular pipeline to choose the optimal measurement step before the survey, which will allow to reduce the error. Explanations are given on the choice of the maximum step of the study based on the strength characteristics of the pipeline. A calculation is provided that confirms the adequacy of the developed mathematical models and the possibility of their application in practice.

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