Shakedown Boundary and Limit Load Determination of a 90-Degree Back to Back Pipe Bend Subjected to Steady Internal Perssures and Cyclic In-Plane Bending Moments

2013 ◽  
Author(s):  
Hany F. Abdalla
Keyword(s):  
Limit Load ◽  
Bending Moments ◽  
Pipe Bend ◽  
Shakedown Analysis ◽  
Plane Bending ◽  
Piping Networks ◽  
Aero Engines ◽  
Shakedown Limit ◽  
Elastic Shakedown ◽  
Internal Pressures

Shakedown analysis of 90–degree back–to–back pipe bends is scarce within open literature. According the author’s knowledge, no shakedown analysis exists for such structure based on experimental data. Ninety degree back–to–back pipe bends are extensively utilized within piping networks of nuclear submarines and modern turbofan aero–engines where space limitation is considered a paramount concern. Additionally, on larger scales, 90–degree back–to–back pipe bend configurations are also found within piping networks of huge liquefied natural gas tankers. The structure analyzed is formed by bending a straight pipe to acquire the geometry of two 90–degree pipe bends set back–to–back each having a nominal pipe size (NPS) of 10 in. Schedule 40 Standard (STD). In the current research, the 90–degree back–to–back pipe bend setup analyzed is subjected to a spectrum of steady internal pressures and cyclic in–plane bending moments. A previously developed simplified technique for determining elastic shakedown limit loads is utilized to generate the elastic shakedown boundary of the 90–degree back–to–back pipe bend analyzed. In addition to determining the elastic shakedown boundary, elastic and post shakedown domains (Bree diagram), the maximum moment carrying capacities (limit moments) are also determined and imposed on the generated Bree diagram of the analyzed structure. The simplified technique outcomes showed excellent correlation with the results of full elastic–plastic cyclic loading finite element simulations.

Shakedown Boundary of a 90–Degree Back–to–Back Pipe Bend Subjected to Steady Internal Pressures and Cyclic Out–of–Plane Bending Moments

2014 ◽  
Author(s):  
Hany F. Abdalla
Keyword(s):  
Internal Pressure ◽  
Bending Moment ◽  
Bending Moments ◽  
Pipe Bend ◽  
Structure Comparison ◽  
Out Of Plane ◽  
Plane Bending ◽  
Shakedown Limit ◽  
Elastic Shakedown ◽  
Internal Pressures

Ninety degree back–to–back pipe bends are extensively utilized within piping networks of modern nuclear submarines and modern turbofan aero–engines where space limitation is considered a supreme concern. According the author’s knowledge, no shakedown analysis exists for such structure based on experimental data. In the current research, the pipe bend setup analyzed is subjected to a spectrum of steady internal pressures and cyclic out–of–plane bending moments. A previously developed direct non–cyclic simplified technique, for determining elastic shakedown limit loads, is utilized to generate the elastic shakedown boundary of the analyzed structure. Comparison with the elastic shakedown boundary of the same structure, but subjected to cyclic in–plane bending moments revealed a higher shakedown boundary for the out–of–plane bending loading configuration with a maximum bending moment ratio of 1.4 within the low steady internal pressure spectrum. The ratio decreases towards the medium to high internal pressure spectrum. The simplified technique outcomes showed excellent correlation with the results of full elastic–plastic cyclic loading finite element simulations.

Shakedown Limit Load Determination of a Cylindrical Vessel–Nozzle Intersection Subjected to Steady Internal Pressures and Cyclic In-Plane Bending Moments

2014 ◽  
Vol 136 (5) ◽  
Author(s):  
Hany F. Abdalla
Keyword(s):  
Limit Load ◽  
Cylindrical Vessel ◽  
Bending Moments ◽  
Limit Loads ◽  
Capacity Limit ◽  
Plane Bending ◽  
Shakedown Limit ◽  
Elastic Shakedown ◽  
Internal Pressures

In the current research, the elastic shakedown limit loads for a cylindrical vessel–nozzle intersection is determined via a direct noncyclic simplified technique. The cylindrical vessel–nozzle intersection is subjected to a spectrum of steady internal pressure magnitudes and cyclic in-plane bending moments on the nozzle end. The determined elastic shakedown limit loads are utilized to generate the elastic shakedown boundary (Bree diagram) of the cylindrical vessel–nozzle structure. Additionally, the maximum moment carrying capacity (limit moments) and the elastic limit loads are determined and imposed on the Bree diagram of the structure. The simplified technique outcomes showed excellent correlation with the results of full cyclic loading elastic–plastic finite element simulations.

Shakedown Limit Loads for 90 Degree Scheduled Pipe Bends Subjected to Steady Internal Pressure and Cyclic Bending Moments

2011 ◽  
Vol 133 (3) ◽  
Author(s):  
Hany F. Abdalla ◽  
Mohammad M. Megahed ◽  
Maher Y. A. Younan
Keyword(s):  
Finite Element ◽  
Internal Pressure ◽  
Pressure Vessel ◽  
Limit Load ◽  
Small Displacement ◽  
Bending Moments ◽  
Pipe Bend ◽  
Hardening Material ◽  
Cyclic Bending ◽  
Shakedown Limit

A simplified technique for determining the shakedown limit load for a long radius 90 deg pipe bend was previously developed (Abdalla, H. F., et al., 2006, “Determination of Shakedown Limit Load for a 90 Degree Pipe Bend Using a Simplified Technique,” ASME J. Pressure Vessel Technol., 128, pp. 618–624; Abdalla, H. F., et al., 2007, “Shakedown Limits of a 90-Degree Pipe Bend Using Small and Large Displacement Formulations,” ASME J. Pressure Vessel Technol., 129, pp. 287–295). The simplified technique utilizes the finite element (FE) method and employs the small displacement formulation to determine the shakedown limit load (moment) without performing lengthy time consuming full cyclic loading finite element simulations or utilizing conventional iterative elastic techniques. The shakedown limit load is determined through the calculation of residual stresses developed within the pipe bend structure. In the current paper, a parametric study is conducted through applying the simplified technique on three scheduled pipe bends, namely, nominal pipe size (NPS) 10 in. Sch. 20, NPS 10 in. Sch. 40 STD, and NPS 10 in. Sch. 80. Two material models are assigned, namely, an elastic perfectly plastic (EPP) material and an idealized elastic-linear strain hardening material obeying Ziegler’s linear kinematic hardening (KH) rule. This type of material model is termed in the current study as the KH-material. The pipe bends are subjected to a spectrum of steady internal pressure magnitudes and cyclic bending moments. The cyclic bending includes three different loading patterns, namely, in-plane closing, in-plane opening, and out-of-plane bending moment loadings of the pipe bends. The shakedown limit moments outputted by the simplified technique are used to generate shakedown diagrams of the scheduled pipe bends for the spectrum of steady internal pressure magnitudes. A comparison between the generated shakedown diagrams for the pipe bends employing the EPP- and the KH-materials is presented. Relatively higher shakedown limit moments were recorded for the pipe bends employing the KH-material at the medium to high internal pressure magnitudes.

Shakedown Limit Load Determination for a Kinematically Hardening 90 deg Pipe Bend Subjected to Steady Internal Pressures and Cyclic Bending Moments

2011 ◽  
Vol 133 (5) ◽  
Author(s):  
Hany F. Abdalla ◽  
Maher Y. A. Younan ◽  
Mohammad M. Megahed
Keyword(s):  
Cyclic Loading ◽  
Internal Pressure ◽  
Limit Load ◽  
Material Model ◽  
Small Displacement ◽  
Bending Moments ◽  
Pipe Bend ◽  
Cyclic Bending ◽  
Fe Simulations ◽  
Shakedown Limit

A simplified technique for determining the lower bound shakedown limit load of a structure, employing an elastic–perfectly plastic (EPP) material model, was previously developed and successfully applied to a long radius 90 deg pipe bend (Abdalla et al., 2006, “Determination of Shakedown Limit Load for a 90 Degree Pipe Bend Using a Simplified Technique,” ASME J. Pressure Vessel Technol., 128, pp. 618–624). The pipe bend is subjected to steady internal pressure magnitudes and cyclic bending moments. The cyclic bending includes three different loading patterns, namely, in-plane closing, in-plane opening, and out-of-plane bending moment loadings. The simplified technique utilizes the finite element (FE) method and employs a small displacement formulation to determine the shakedown limit load without performing lengthy time consuming full elastic-plastic (ELPL) cyclic loading FE simulations or conventional iterative elastic techniques. In the present research, the simplified technique is further modified to handle structures employing an elastic-linear strain hardening material model following Ziegler’s linear kinematic hardening (KH) rule. The shakedown limit load is determined through the calculation of residual stresses developed within the pipe bend structure accounting for the back stresses, determined from the KH shift tensor, responsible for the rigid translation of the yield surface. The outcomes of the simplified technique showed an excellent correlation with the results of full ELPL cyclic loading FE simulations. The shakedown limit moments output by the simplified technique are utilized to generate shakedown diagrams (Bree diagrams) of the pipe bend for a spectrum of steady internal pressure magnitudes. The generated Bree diagrams are compared with the ones previously generated employing the EPP material model. These indicated relatively conservative shakedown limit moments compared with the ones employing the KH rule.

Shakedown Limit Loads for 90-Degree Scheduled Pipe Bends Subjected to Constant Internal Pressure and Cyclic Bending Moments

2008 ◽  
Author(s):  
Hany F. Abdalla ◽  
Mohammad M. Megahed ◽  
Maher Y. A. Younan
Keyword(s):  
Finite Element ◽  
Internal Pressure ◽  
Kinematic Hardening ◽  
Limit Load ◽  
Small Displacement ◽  
Bending Moments ◽  
Pipe Bend ◽  
Hardening Material ◽  
Cyclic Bending ◽  
Shakedown Limit

A simplified technique for determining the shakedown limit load for a long radius 90-degree pipe bend was previously developed [1, 2]. The simplified technique utilizes the finite element method and employs the small displacement formulation to determine the shakedown limit load (moment) without performing lengthy time consuming full cyclic loading finite element simulations or utilizing conventional iterative elastic techniques. The shakedown limit load is determined through the calculation of residual stresses developed within the pipe bend structure. In the current paper, a parametric study is conducted through applying the simplified technique on three scheduled pipe bends namely: NPS (Nominal Pipe Size) 10" Sch. No. 20, NPS 10" Sch. No. 40 STD, and NPS 10" Sch. No. 80. Two material models are assigned namely; an elastic-perfectly-plastic (EPP) material and an idealized elastic-linear strain hardening material obeying Ziegler’s linear kinematic hardening (KH) rule. This type of material model is termed in the current study as the KH-material. The pipe bends are subjected to a spectrum of constant internal pressure magnitudes and cyclic bending moments. The cyclic bending includes three different loading patterns namely: in-plane closing (IPC), in-plane opening (IPO), and out-of-plane (OP) bending moment loadings of the pipe bends. The shakedown limit moments output by the simplified technique are used to generate shakedown diagrams of the scheduled pipe bends for the spectrum of constant internal pressure magnitudes. A comparison between the generated shakedown diagrams for the pipe bends employing the EPP- and the KH-materials is presented. Relatively higher shakedown limit moments were recorded for the pipe bends employing the KH-material at the medium to high internal pressure magnitudes.

A Proposal for a Simplified Assessment Procedure to API-579 Standard

2015 ◽  
Vol 137 (3) ◽  
Author(s):  
Youssef A. F. Hafiz ◽  
Maher Y. A. Younan ◽  
Hany F. Abdalla
Keyword(s):  
Residual Stress ◽  
Parametric Study ◽  
Limit Load ◽  
Assessment Procedure ◽  
Elastic Plastic ◽  
Shakedown Limit ◽  
Elastic Shakedown ◽  
Assessment Procedures ◽  
Internal Pressures ◽  
Good Agreement

The objective of this research paper is to propose, to API 579 standard, a simplified assessment procedure for shakedown limit load determination. The proposed assessment procedure applies the Simplified Technique, replacing the existing iterative elastic–plastic API 579 assessment procedures. The technique applies only two analyses (elastic and elastic–plastic) to determine the elastic shakedown limit. The shakedown limit load is determined from the residual stress that is calculated from the scaled elastic stress and subtracted from the elastic–plastic. Finally, to determine the shakedown limit from the residual stress calculated. For the purpose of validating the new assessment procedure to be applied to locally thinned-wall components, the shakedown boundary of a locally thinned-wall pipe-branch connection subjected to a spectrum of steady internal pressures and cyclic bending moments is generated. The results of the proposed assessment procedure are successfully verified against the existing API 579 elastic and elastic–plastic assessment procedures. A parametric study is performed through changing both the depth and location of the local wall thinning within the pipe-branch connection. The results of the parametric study show good agreement in the shakedown limit boundary results with the API 579 elastic–plastic stress analysis procedure.

Shakedown Analysis of a Cylindrical Vessel-Nozzle Intersection Subjected to Steady Internal Pressures and Cyclic Out-of-Plane Bending Moments

2012 ◽  
Author(s):  
Hany F. Abdalla ◽  
Maher Y. A. Younan ◽  
Mohammad M. Megahed
Keyword(s):  
Elastic Limit ◽  
Cylindrical Vessel ◽  
Bending Moments ◽  
Excellent Correlation ◽  
Limit Loads ◽  
Capacity Limit ◽  
Out Of Plane ◽  
Plane Bending ◽  
Shakedown Limit ◽  
Internal Pressures

In the current research, the shakedown limit loads of a cylindrical vessel–nozzle intersection are determined via a simplified technique. The cylindrical vessel–nozzle intersection is subjected to a spectrum of steady internal pressure magnitudes and cyclic out–of–plane bending moments on the nozzle. The determined shakedown limit loads, forming the shakedown boundary, are utilized to generate the Bree diagram of the cylindrical vessel–nozzle intersection. In addition to the determined shakedown boundary, the Bree diagram includes the maximum moment carrying capacity (limit moments) and the elastic limit loads. The currently generated Bree diagram is compared with previously generated Bree diagram of the same structure, but subjected to in–plane bending. Noticeable differences regarding the magnitudes of the generated shakedown boundaries are observed. Moreover, only failure due to reversed plasticity response occurs upon exceeding the generated shakedown boundary unlike cyclic in–plane bending where the structure experienced both reversed plasticity and ratchetting failure responses. The simplified technique outcomes showed excellent correlation with the results of full elastic–plastic cyclic loading finite element simulations.

Shakedown Limit Load Determination for a Kinematically Hardening 90-Degree Pipe Bend Subjected to Constant Internal Pressure and Cyclic Bending

2007 ◽  
Author(s):  
Hany F. Abdalla ◽  
Mohammad M. Megahed ◽  
Maher Y. A. Younan
Keyword(s):  
Finite Element ◽  
Internal Pressure ◽  
Plastic Material ◽  
Kinematic Hardening ◽  
Limit Load ◽  
Material Behavior ◽  
Pipe Bend ◽  
Cyclic Bending ◽  
Perfectly Plastic ◽  
Shakedown Limit

A simplified technique for determining the shakedown limit load of a structure employing an elastic-perfectly-plastic material behavior was previously developed and successfully applied to a long radius 90-degree pipe bend. The pipe bend is subjected to constant internal pressure and cyclic bending. The cyclic bending includes three different loading patterns namely; in-plane closing, in-plane opening, and out-of-plane bending moment loadings. The simplified technique utilizes the finite element method and employs small displacement formulation to determine the shakedown limit load without performing lengthy time consuming full cyclic loading finite element simulations or conventional iterative elastic techniques. In the present paper, the simplified technique is further modified to handle structures employing elastic-plastic material behavior following the kinematic hardening rule. The shakedown limit load is determined through the calculation of residual stresses developed within the pipe bend structure accounting for the back stresses, determined from the kinematic hardening shift tensor, responsible for the translation of the yield surface. The outcomes of the simplified technique showed very good correlation with the results of full elastic-plastic cyclic loading finite element simulations. The shakedown limit moments output by the simplified technique are used to generate shakedown diagrams of the pipe bend for a spectrum of constant internal pressure magnitudes. The generated shakedown diagrams are compared with the ones previously generated employing an elastic-perfectly-plastic material behavior. These indicated conservative shakedown limit moments compared to the ones employing the kinematic hardening rule.

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