Closed-Form Plastic Collapse Loads of Pipe Bends Under Combined Pressure and In-Plane Bending

2006 ◽  
Author(s):  
Chang-Sik Oh ◽  
Yun-Jae Kim
Keyword(s):  
Closed Form ◽  
Three Dimensional ◽  
Plastic Collapse ◽  
Plastic Limit ◽  
Perfectly Plastic ◽  
Plastic Materials ◽  
Bending Mode ◽  
Wide Range ◽  
Plane Bending ◽  
Elastic Perfectly Plastic

Based on three-dimensional (3-D) FE limit analyses, this paper provides plastic limit, collapse and instability load solutions for pipe bends under combined pressure and in-plane bending. The plastic limit loads are determined from FE limit analyses based on elastic-perfectly plastic materials using the small geometry change option, and the FE limit analyses using the large geometry change option provide plastic collapse loads (using the twice-elastic-slope method) and instability loads. For the bending mode, both closing bending and opening bending are considered, and a wide range of parameters related to the bend geometry is considered. Based on the FE results, closed-form approximations of plastic limit and collapse load solutions for pipe bends under combined pressure and bending are proposed.

Plastic Limit Loads for Piping Branch Junctions

2007 ◽  
Vol 345-346 ◽  
pp. 1377-1380 ◽  
Author(s):  
Yun Jae Kim ◽  
Kuk Hee Lee ◽  
Chi Yong Park
Keyword(s):  
Three Dimensional ◽  
Limit Load ◽  
Plastic Limit ◽  
Perfectly Plastic ◽  
Plastic Materials ◽  
Wide Range ◽  
Pipe Radius ◽  
Plastic Limit Load ◽  
The Mean ◽  
Elastic Perfectly Plastic

The present work presents plastic limit load solutions for branch junctions under internal pressure and in-plane bending, based on detailed three-dimensional (3-D) FE limit analyses using elastic-perfectly plastic materials. The proposed solutions are valid for a wide range of branch junction geometries; ratios of the branch-to-run pipe radius and thickness from 0.0 to 1.0, and the mean radius-to-thickness ratio of the run pipe from 5.0 to 20.0.

Limit Loads for Circumferential Cracked Pipe Bends under In-Plane Bending

2006 ◽  
Vol 321-323 ◽  
pp. 38-42
Author(s):  
Yun Jae Kim ◽  
Chang Sik Oh ◽  
Bo Kyu Park ◽  
Young Il Kim
Keyword(s):  
Three Dimensional ◽  
Surface Cracks ◽  
Plastic Limit ◽  
Limit Loads ◽  
Perfectly Plastic ◽  
Plastic Materials ◽  
Dimensional Finite Element ◽  
Plane Bending ◽  
Elastic Perfectly Plastic ◽  
Three Dimensional Finite Element

This paper presents limit loads for circumferential cracked pipe bends under in-plane bending, based on detailed three-dimensional finite element limit analyses. FE analyses are performed based on elastic-perfectly-plastic materials and the geometrically linear assumption. Both through-wall cracks and part-through surface cracks (having constant depths) are considered, together with different crack locations (extrados and intrados). Based on the FE results, closed-form approximations are proposed for plastic limit loads of pipe bends. It is found that limit loads of pipe bends are smaller than those of straight pipes, but are close for deep and long cracks.

Finite Element Limit Loads for Circumferential Through-Wall Cracked Pipe Bends Under In-Plane Bending

2006 ◽  
Author(s):  
Yun-Jae Kim ◽  
Chang-Sik Oh ◽  
Young-Il Kim ◽  
Chi-Yong Park
Keyword(s):  
Finite Element ◽  
Three Dimensional ◽  
Small Strain ◽  
Plastic Limit ◽  
Crack Location ◽  
Perfectly Plastic ◽  
Dimensional Finite Element ◽  
Plane Bending ◽  
Elastic Perfectly Plastic ◽  
Three Dimensional Finite Element

This paper proposes plastic limit and collapse loads for circumferential through-wall cracked pipe bends under in-plane bending, based on three-dimensional finite element limit analyses. The material is assumed to be elastic-perfectly-plastic, but both the geometrically linear (small strain) and the geometrically nonlinear (large geometry change) options are employed. Regarding crack location, both extrados and intrados cracks are considered. Moreover, for practical application, closed-form approximations of plastic limit and collapse loads are proposed based on the FE results, and compared with corresponding solutions for straight pipes.

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.

Plastic Limit Loads for Through-Wall Cracked Pipes Using Finite Element Limit Analysis

2006 ◽  
Vol 321-323 ◽  
pp. 724-728
Author(s):  
Nam Su Huh ◽  
Yoon Suk Chang ◽  
Young Jin Kim
Keyword(s):  
Finite Element ◽  
Limit Analysis ◽  
Structural Integrity ◽  
Three Dimensional ◽  
Limit Load ◽  
Plastic Behavior ◽  
Plastic Limit ◽  
Integrity Assessment ◽  
Perfectly Plastic ◽  
Elastic Perfectly Plastic

The present paper provides plastic limit load solutions for axial and circumferential through-wall cracked pipes based on detailed three-dimensional (3-D) finite element (FE) limit analysis using elastic-perfectly plastic behavior. As a loading condition, both single and combined loadings are considered. Being based on detailed 3-D FE limit analysis, the present solutions are believed to be valuable information for structural integrity assessment of cracked pipes.

Use of API 579-1/ASME FFS-1 Limit-Load Criteria for Establishing Load Limits for Pressure Vessel Internals

2010 ◽  
Author(s):  
Brian R. Macejko
Keyword(s):  
Closed Form ◽  
Pressure Vessel ◽  
Limit Load ◽  
Process Equipment ◽  
Maximum Pressure ◽  
Plastic Collapse ◽  
Closed Form Solutions ◽  
Perfectly Plastic ◽  
Section Viii ◽  
Elastic Perfectly Plastic

The 2007 edition of ASME Boiler & Pressure Vessel Code Section VIII Division 2 and the 2007 edition of Fitness-For-Service API 579-1/ASME FFS-1 provide the option to use the limit-load method to assess protection against plastic collapse for components of pressurized process equipment. Per the methodology presented therein, the allowable load on a component is established by applying design factors to the elastic-perfectly plastic limit-load such that the onset of gross plastic deformation (plastic collapse) will not occur. Typically, the design limitations of pressure vessel internal components have been assessed through closed form solutions with conservative assumptions. It has been found that the maximum pressure delta across vessel internals established through closed form solutions can become limiting in determination of time between equipment shutdowns. This paper will outline a practical example of industry applied use of the limit-load method to qualify extended limits on mechanical loads applied to pressure vessel internals.

Closed-Form Collapse Moment Equations of Throughwall Circumferentially Cracked Elbows Subjected to In-Plane Bending Moment

2004 ◽  
Vol 126 (3) ◽  
pp. 307-317 ◽  
Author(s):  
J. Chattopadhyay ◽  
A. K. S. Tomar ◽  
B. K. Dutta ◽  
H. S. Kushwaha
Keyword(s):  
Closed Form ◽  
Bending Moment ◽  
Moment Equations ◽  
Element Analysis ◽  
Perfectly Plastic ◽  
Circumferential Crack ◽  
Opening Mode ◽  
Plane Bending ◽  
Elastic Perfectly Plastic ◽  
Bending Modes

A large throughwall circumferential crack in an elbow subjected to in-plane bending moment can significantly reduce its collapse load. Therefore, it is very important to know the collapse moment of an elbow in the presence of a throughwall circumferential crack. The existing closed-form collapse moment equations of throughwall circumferentially cracked elbows are either too conservative or inadequate to correctly quantify the weakening effect due to the presence of the crack, especially for opening mode of bending moment. Therefore, the present study has been carried out to investigate through elastic-plastic finite element analysis the effect of a throughwall circumferential crack on the collapse moment of an elbow under in-plane bending moment. A total of 72 cases of elbows with various sizes of circumferential cracks (2θ=0–150 deg), different wall thickness (R/t=5–20), different elbow bend radii Rb/R=2,3 and two different bending modes, namely closing and opening have been considered in the analysis. Elastic-perfectly plastic stress-strain response of material has been assumed. Collapse moments have been evaluated from moment-end rotation curves by twice-elastic slope method. From these results, closed-form expressions have been proposed to evaluate collapse moments of elbows under closing and opening mode of bending moment. The predictions of these proposed equations have been compared with 8 published elbow test data and are found to be within ±11% variation except for one case.

Reference Stress Solutions for Idealized Branch Junctions

2007 ◽  
Author(s):  
Yun-Jae Kim ◽  
Kuk-Hee Lee
Keyword(s):  
Three Dimensional ◽  
Limit Load ◽  
Perfectly Plastic ◽  
Reference Stress ◽  
Plastic Materials ◽  
Pipe Radius ◽  
Plastic Limit Load ◽  
The Mean ◽  
Elastic Perfectly Plastic ◽  
Good Agreement

The present work presents plastic limit load solutions for thin-walled branch junctions under internal pressure and in-plane bending, based on detailed three-dimensional (3-D) FE limit analyses using elastic-perfectly plastic materials. The proposed solutions are valid to ratios of the branch-to-run pipe radius and thickness from 0.0 to 1.0, and the mean radius-to-thickness ratio of the run pipe from 5.0 to 20.0. Comparison with FE results shows good agreement.

Limit loads for thin‐walled piping branch junctions under combined pressure and in‐plane bending

2008 ◽  
Vol 43 (2) ◽  
pp. 87-108 ◽  
Author(s):  
Y‐J Kim ◽  
K‐H Lee ◽  
C‐Y Park
Keyword(s):  
Branch Pipe ◽  
Three Dimensional ◽  
Limit Load ◽  
Small Strain ◽  
Limit Loads ◽  
Perfectly Plastic ◽  
Dimensional Finite Element ◽  
Plane Bending ◽  
Elastic Perfectly Plastic ◽  
Three Dimensional Finite Element

Closed‐form yield loci are proposed for branch junctions under combined pressure and in‐plane bending, via small‐strain three‐dimensional finite element (FE) limit load analyses using elastic—perfectly plastic materials. Two types of bending loading are considered: bending on the branch pipe and that on the run pipe. For bending on the run pipe, the effect of the bending direction is further considered. Comparison with extensive FE results shows that predicted limit loads using the proposed solutions are overall conservative and close to FE results. The proposed solutions are believed to be valid for the branch‐to‐run pipe ratios of radius and of thickness from 0.0 to 1.0, and the mean radius‐to‐thickness ratio of the run pipe from 5.0 to 20.0.

On Plastic Collapse of Media With Random Yield Strength

2001 ◽  
Vol 68 (5) ◽  
pp. 715-724 ◽  
Author(s):  
A. P.-D. Ku ◽  
R. P. Nordgren
Keyword(s):  
Yield Strength ◽  
Plane Problem ◽  
Gaussian Random Field ◽  
Three Dimensional ◽  
Upper And Lower Bounds ◽  
Plastic Collapse ◽  
Variable Yield ◽  
Perfectly Plastic ◽  
Fixed Load ◽  
Elastic Perfectly Plastic

This paper concerns the plastic collapse of an elastic/perfectly plastic medium with randomly variable yield strength under a fixed load. The yield strength is represented by a Gaussian random field of known statistical properties. Using the theorems of limit analysis and the methods of reliability theory, algorithms are developed for the computation of upper and lower bounds on the probability of plastic collapse. By varying the magnitude of the fixed load, bounds on the probability distribution function for the collapse load can be computed. Results are given for uniform pressure applied to a rectangular region of the surface of an elastic/plastic half-space. For the corresponding plane problem, results for the classical Hill and Prandtl failure mechanisms are compared. Three-dimensional results are found to differ significantly from those of the plane problem. Comparison is made with results of a previous approximate method for three-dimensional problems.

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