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 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 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.

On the Conditions to Prevent Plastic Shakedown of Structures: Part II—The Plastic Shakedown Limit Load

1993 ◽  
Vol 60 (1) ◽  
pp. 20-25 ◽  
Author(s):  
Castrenze Polizzotto
Keyword(s):  
Mechanical Load ◽  
Plastic Material ◽  
Limit State ◽  
Limit Load ◽  
Companion Paper ◽  
Material Structure ◽  
Perfectly Plastic ◽  
Shakedown Limit ◽  
Elastic Shakedown ◽  
Plastic Shakedown

Following the results of a companion paper, the concept of plastic shakedown limit load is introduced for an elastic-perfectly plastic material structure subjected to combined cyclic (mechanical and/or kinematical) loads and steady (mechanical) load. Static and kinematic approaches are available for the computation of this load, in perfect analogy with the classic (elastic) shakedown limit load. The plastic shakedown limit state of the structure being in an impending alternating plasticity collapse is studied and a number of interesting features of it are pointed out.

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.

Determination of Shakedown Limit Load for a 90-Degree Pipe Bend Using a Simplified Technique

2006 ◽  
Vol 128 (4) ◽  
pp. 618-624 ◽  
Author(s):  
Hany F. Abdalla ◽  
Mohammad M. Megahed ◽  
Maher Y. A. Younan
Keyword(s):  
Finite Element ◽  
Cyclic Loading ◽  
Internal Pressure ◽  
Bending Moment ◽  
Limit Load ◽  
Heat Fluxes ◽  
Bench Mark ◽  
Pipe Bend ◽  
Elastic Plastic ◽  
Shakedown Limit

In this paper a simplified technique is presented to determine the shakedown limit load of a 90-degree pipe bend subjected to constant internal pressure and cyclic in-plane closing bending moment using the finite element method. The simplified technique determines the shakedown limit load without performing time consuming full elastic-plastic cyclic loading simulations or conventional iterative elastic techniques. Instead, the shakedown limit load is determined by performing two finite element analyses namely; an elastic analysis and an elastic-plastic analysis. By extracting the results of the two analyses, the shakedown limit load is determined through the calculation of the residual stresses developed in the pipe bend. In order to gain confidence in the simplified technique, the output shakedown limit moments are used to perform full elastic-plastic cyclic loading simulations to check for shakedown behavior of the pipe bend. The shakedown limit moments output by the simplified technique are used to generate the shakedown diagram of the pipe bend for a range of constant internal pressure magnitudes. The maximum moment carrying capacity (limit moment) the pipe bend can withstand and the elastic limit are also determined and imposed on the shakedown diagram of the pipe bend. In order to get acquainted with the simplified technique, it is applied beforehand to a bench mark shakedown problem namely, the Bree cylinder (Bree, J., 1967, J. Strain Anal., 3, pp. 226–238) problem. The Bree cylinder is subjected to constant internal pressure and cyclic high heat fluxes across its wall. The results of the simplified technique showed very good correlation with the analytically determined Bree diagram of the cylinder.

scholarly journals Residual stress redistribution during elastic shake down in welded plates

2018 ◽  
Vol 165 ◽  
pp. 21004
Author(s):  
Jazeel R. Chukkan ◽  
Guiyi Wu ◽  
Michael E. Fitzpatrick ◽  
Elvin Eren ◽  
Xiang Zhang ◽  
...  
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Base Material ◽  
Offshore Structures ◽  
Residual Stress Field ◽  
Mixed Hardening ◽  
Weld Residual Stress ◽  
Shakedown Limit ◽  
Elastic Shakedown ◽  
Different Levels

Residual stresses are a consequence of welding in various structures such as ships and offshore structures. Residual stresses can be relaxed or redistributed according to the load levels during operation. The elastic shakedown phenomenon can be considered as one of the reasons for this change. This paper studies the relaxation/redistribution of weld residual stress during different levels of shakedown in a butt-welded plate chosen according to ship design and welding procedures. Welding was performed on DH36, a ship structural steel. Neutron diffraction was used to measure residual stresses in these plates in the as-welded state and after different levels of shakedown. A mixed hardening model in line with the Chaboche model is determined for both weld and base material. A numerical model is developed to estimate the shakedown limit on butt-welded plate. Further, the redistribution of residual stress in a numerical weld model according to the different levels of shakedown limit is studied. Based on the shakedown limit of the butt-welded plate, a shakedown region is determined, where the structure will undergo elastic shakedown in the presence of an existing residual stress field if the maximum stress on the load section after a few initial cycles is in the shakedown region.

Limit and Shakedown Loads Determination for Locally Thinned Wall Pipe Branch Connection Subjected to Pressure and Bending Moments

2012 ◽  
Author(s):  
Youssef A. F. Hafiz ◽  
Maher Y. A. Younan ◽  
Hany F. Abdalla
Keyword(s):  
Numerical Models ◽  
Bending Moment ◽  
Limit Load ◽  
Tension Stress ◽  
Assessment Procedure ◽  
Wall Thinning ◽  
Out Of Plane ◽  
Plane Bending ◽  
Shakedown Limit ◽  
Local Wall Thinning

In this paper the shakedown limit load for unreinforced locally thinned wall pipe branch connection is determined using the Simplified Technique. Loadings were considered to be internal pressure, as a steady load, with in-plane bending or with out-of-plane bending applied on the branch, as alternating loads. Two locations of local wall thinning were taken; one was on the run pipe opposite to the branch and other on the branch at the maximum tension stress side of the bending moment applied whether in in-plane or out-of-plane situation. Two Finite Element (FE) limit load models were used to verify the modeling of the pipe branch connection with its local wall thinning. First model results were compared with experimental data taken from the literature, and the second results were compared with numerical models taken also from the literature and also compared with API 579 “Fitness For Service” (FFS), part-five, level-two assessment procedure. First and second comparisons lead to good agreement but for API 579 comparison it was found that it is slightly changing with the depth of the local wall thinning but does not reflect the expected behavior of the limit load as the FEA models showed. For the results of the shakedown limit load analysis, Bree diagrams were constructed to show elastic, shakedown and plastic collapse regions. Then, comparison was made to show the effect of the local wall thinning depth and location on previous limits. Finally, the shakedown results were verified using the elastic-plastic ratcheting analysis of API 579, level three assessment and it showed successfully the shakedown, ratcheting and reversed plasticity regions. This verifications and results can prove that the Simplified Technique can be used as a level-three ratcheting assessment in API 579.

Limit and Shakedown Analysis of 45-Degree Piping Elbows Under Internal Pressure and In-Plane Bending

2020 ◽  
Vol 142 (2) ◽  
Author(s):  
Heng Peng ◽  
Jun Shen ◽  
Yinghua Liu ◽  
Haofeng Chen
Keyword(s):  
Internal Pressure ◽  
Limit Load ◽  
Plastic Limit ◽  
Element Analysis ◽  
Shakedown Analysis ◽  
Integrity Assessment ◽  
Elastic Plastic ◽  
Computation Efficiency ◽  
Interaction Curves ◽  
Shakedown Limit

Abstract This paper carries out the limit and shakedown analysis of 45 deg piping elbows made up of elastic–perfectly plastic materials by means of the recently proposed stress compensation method (SCM). The elbows are subjected to steady internal pressure and cyclic in-plane closing, opening, and reversed bending moments. Different geometries of the piping elbows and various combinations of these applied loads are investigated to generate various plastic limit and shakedown limit load interaction curves. The plastic limit bending moment and plastic limit internal pressure calculated with the SCM are compared to those determined by the twice-elastic-slope approach. Full step-by-step (SBS) elastic–plastic incremental finite element analysis (FEA) is utilized to verify the structural cyclic responses on both sides of the curves obtained and further to confirm the correct shakedown limit loads and boundaries. It is shown that the SCM calculates the shakedown limit load accurately and possesses about 40 times the computation efficiency of the SBS elastic–plastic incremental method. The effects of the ratios of mean radius to wall thickness and bending radius to mean radius of the piping elbow as well as the loading conditions on the plastic limit and shakedown limit load interaction curves are presented. The results presented in this work give a comprehensive understanding of long-term response behaviors of the piping elbow subjected to cyclic loadings and provide some guidance for the design and integrity assessment of piping systems.

Shakedown and Limit Analysis of 45-Degree Piping Elbows Under Internal Pressure and Cyclic In-Plane Bending

2019 ◽  
Author(s):  
Heng Peng ◽  
Yinghua Liu
Keyword(s):  
Internal Pressure ◽  
Limit Analysis ◽  
Limit Load ◽  
Plastic Limit ◽  
Limit Loads ◽  
Integrity Assessment ◽  
Elastic Plastic ◽  
Plastic Limit Load ◽  
Interaction Curves ◽  
Shakedown Limit

Abstract This paper carries out the shakedown and limit analysis of 45-degree piping elbows subjected to steady internal pressure and cyclic in-plane closing, opening and reverse bending moments by means of the recently proposed stress compensation method (SCM). Different geometries of the piping elbows and various combinations of these applied loads are investigated to create various shakedown limit and plastic limit load interaction curves. The plastic limit loads for single internal pressure and single bending moment calculated with the SCM are compared to those calculated with the twice-elastic-slope method. Full step-by-step elastic-plastic incremental finite element analyses are utilized to verify the structural cyclic responses on both sides of the curves obtained and further to confirm the correct shakedown limit loads and boundaries. It is shown that the SCM calculates the shakedown limit load accurately and possess more than 40 times the computational efficiency of the step-by-step elastic-plastic incremental method. The effects of the ratios of bending radius to mean radius and mean radius to wall thickness of the piping elbow as well as loading conditions on shakedown limit and plastic limit load interaction curves are presented. The results presented in this work provide a comprehensive understanding of long term response behaviors of the piping elbow under the combined cyclic loading and offer some essential points to be concerned for the design and integrity assessment of piping systems.

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