Analytical Assessment of the Remaining Strength of Corroded Pipelines and Comparison With Experimental Criteria

2016 ◽  
Vol 139 (3) ◽  
Author(s):  
Sérgio B. Cunha ◽  
Theodoro A. Netto
Keyword(s):  
Analytical Solutions ◽  
Plastic Behavior ◽  
Pipe Material ◽  
Empirical Methods ◽  
Analytical Assessment ◽  
Corrosion Defects ◽  
Geometry Parameterization ◽  
Comparative Results ◽  
Strain Hardening Behavior ◽  
Flaw Shape

Recently published analytical solutions for the remaining strength of a pipeline with narrow axial and axisymmetric volumetric flaws are described in this paper, and their experimental and numerical validation are reviewed. Next, the domains of applicability of each solution are studied, some simplifications suitable to steel pipelines are introduced, and an analytical model for the remaining strength of corroded steel pipelines is presented. This analytical solution is compared with the standards most widely used in the industry for assessment of corroded pipelines: ASME B31G, modified ASME, and DNV RP-F101. The empirical and analytical solutions are compared with respect to their most relevant parameters: critical (or flow) stress, flaw geometry parameterization, and Folias or bulging factor formulation. Finally, two common pipeline steels, API 5L grades X42 and X100, are selected to compare the different corrosion assessment methodologies. Corrosion defects of 75%, 50%, and 25% thickness reduction are evaluated. None of the experimental equations take into account the strain-hardening behavior of the pipe material, and therefore, they cannot properly model materials with very dissimilar plastic behavior. The comparison indicates that the empirical methods underestimate the remaining strength of shallow defects, which might lead to unnecessary repair recommendations. Furthermore, it was found that the use of a parameter employed by some of the empirical equations to model the assumed flaw shape leads to excessively optimistic and nonconservative results of remaining strength for long and deep flaws. Finally, the flaw width is not considered in the experimental criteria, and the comparative results suggest that the empirical solutions are somewhat imprecise to model the burst of wide flaws.

Elastoplastic Analysis of a Miniature Circular Disk Bending Specimen

2008 ◽  
Vol 130 (4) ◽  
Author(s):  
Vishnu Verma ◽  
A. K. Ghosh ◽  
G. Behera ◽  
Kamal Sharma ◽  
R. K. Singh
Keyword(s):  
Finite Element ◽  
Analytical Solutions ◽  
Material Properties ◽  
Finite Element Solution ◽  
Bending Test ◽  
Experimental Result ◽  
Strain Hardening Exponent ◽  
Plastic Behavior ◽  
Element Solution ◽  
Element Analysis

The miniature disk bending test is used to evaluate the mechanical behavior of irradiated materials and their properties (e.g., yield stress and strain hardening exponent) to determine mainly ductility loss in steel due to irradiation from the load-deflection behavior of the disk specimen. In the miniature disk bending machine the specimen is firmly held between the two horizontal jaws of punch, and an indentor with a spherical ball travels vertically. Analytical solutions for large amplitude plastic deformation become rather unwieldy. Hence, a finite element analysis has been carried out. The finite element model considers contact between the indentor and test specimen, friction between various pairs of surfaces, and elastic plastic behavior. This paper presents the load versus deflection results of a parametric study where the values of various parameters defining the material properties have been varied by ±10% around the base values. Some well-known analytical solutions to this problem have also been considered. It is seen that the deflection obtained by analytical elastic bending theory is significantly lower than that obtained by the elastoplastic finite element solution at relatively small values of load. The finite element solution has been compared with one experimental result and values are in reasonably good agreement. With these results it will be possible to determine the material properties from the experimentally obtained values of load and deflection.

Strain-Hardening Topography of Elastic-Plastic Materials

1983 ◽  
Vol 50 (4a) ◽  
pp. 795-801 ◽  
Author(s):  
J. Casey ◽  
H. H. Lin
Keyword(s):  
Strain Hardening ◽  
Type Theory ◽  
Plastic Behavior ◽  
Hardening Behavior ◽  
Perfectly Plastic ◽  
Plastic Materials ◽  
Different Types ◽  
Elastic Plastic Materials ◽  
Strain Hardening Behavior ◽  
Rate Type

In the context of a purely mechanical rate-type theory of plasticity, a special set of constitutive equations is discussed. A method [1,2] of characterizing strain-hardening behavior is utilized to examine the different types of response that may be exhibited. Loci of constant strain-hardening behavior in stress space and regions of hardening, softening, and perfectly plastic behavior are determined.

The Conservatism of Leak Before Break Analysis in Terms of the Applied Moment at Cracked Section

2016 ◽  
Author(s):  
Yeji Kim ◽  
Young-Jin Oh ◽  
Heung-Bae Park
Keyword(s):  
Time History ◽  
Time History Analysis ◽  
Elastic Behavior ◽  
Plastic Behavior ◽  
Pipe Material ◽  
Linear Elastic ◽  
Pipe Model ◽  
History Analysis ◽  
Comparison Results ◽  
Leak Before Break

In leak before break (LBB) analysis, applied moment at the position of a postulated crack is a key parameter. The current procedures of LBB analysis use the value of design basis loads that are calculated with the assumption that the pipe does not contain a crack and follows the linear elastic behavior. Therefore, this can lead to conservative results of LBB evaluation compared with the case that considers the effect of plastic behavior of cracked pipe on the calculation of the applied moment at the cracked section [2]. This paper aims to quantitatively investigate the conservatism of the existing LBB analysis in terms of the applied moment at the cracked section. The calculation results using the current procedures with linear elastic pipe model without a crack were compared with the results from the cracked pipe analysis. To consider nonlinearity of crack behavior and pipe material, the time history analysis methods that were verified using the simulated seismic pipe system experiment in the IPIRG-2 program were employed. The comparison results indicated that the applied moment at the cracked section decreases when the effect of crack and nonlinear behavior are considered in the analysis. Therefore, the current procedures of LBB analysis are significantly conservative compared with the elastic-plastic time history analysis. Base on this detailed analysis, the additional safety margin can be secured in the LBB analysis.

Experimental Investigation Into the Fracture Toughness of Polyethylene Pipe Material

2004 ◽  
Author(s):  
Ihab Mamdouh Graice ◽  
Maher Y. A. Younan ◽  
Soheir Ahmed Radwan Naga
Keyword(s):  
Fracture Toughness ◽  
Crack Opening ◽  
Experimental Tests ◽  
Compact Tension ◽  
Test Method ◽  
Elastic Behavior ◽  
Plastic Behavior ◽  
Specimen Thickness ◽  
Pipe Material ◽  
Opening Displacement

The mechanical behavior of the recently produced gas pipes material PE100 is investigated and compared to the commonly used material PE80 to determine their relative advantages. The two materials show plastic behavior at room temperature. The fracture toughness of the two materials is experimentally determined using the two common elastic plastic fracture mechanics methods: the ASTM multiple specimen test method for determining the J-R curve of the materials, and the crack opening displacement (COD) method. The investigation of the fracture behavior of the two materials includes the effect of the specimen thickness as well as specimen configuration. The experimental tests were carried on the compact tension (CT) specimens and the single edge notch bending (SENB) specimens. At −70°C, the materials show elastic behavior, the ASTM test method for determining fracture toughness is applied to SENB specimens to determine KIC of both materials. PE80 shows greater resistance to fracture than PE100.

Simulation of nonlinear circuits with alternating current in MatLab system

2020 ◽  
pp. 80-89
Author(s):  
A.V. Kupova ◽  
◽  
E.V. Lanovenko ◽  
E.B. Solovyeva ◽  
◽  
...  
Keyword(s):  
Information Technology ◽  
Numerical Modeling ◽  
Analytical Solutions ◽  
Analytical Modeling ◽  
Nonlinear Circuits ◽  
Electrical Circuits ◽  
Nonlinear Inductance ◽  
Comparative Results ◽  
Task Conditions ◽  
Theoretical Foundations

Information technology optimizes the process of studying the theoretical foundations of electrical engineering. Analytical solutions are often accompanied by complex mathematical transformations. In this case, the simulation (numerical modeling) reduces the calculation time and enables to take into consideration of changing the task conditions, evaluating the distinction of results, etc. The simulation of electrical circuits with a nonlinear inductance and a transformer is carried out in the MatLab system using the Simscape library. The comparative results analysis of analytical modeling and simulation of these circuits is represented.

The applicability of analytical elasto-plastic solutions and issues of the formation of shear bands zones

2020 ◽  
Author(s):  
Elena Grishko ◽  
Artyom Myasnikov ◽  
Denis Sabitov ◽  
Yuri Podladchikov ◽  
Aboozar Garavand
Keyword(s):  
Plastic Deformation ◽  
Finite Element ◽  
Analytical Solutions ◽  
Applied Mathematics ◽  
Shear Bands ◽  
Wellbore Stability ◽  
Plastic Behavior ◽  
Frictional Material ◽  
Support Of Research ◽  
Element Technique

<p><strong>Key Words:</strong> numerical modelling, elasto-plastic analytical solutions, shear bands, geomechanics.</p><p>The correct analysis of wellbore stability in unconventional reservoirs receives much interest from the industry as shale rock and tar sands demonstrate perceptible plastic behavior which influences the estimation of rock failure. To tackle this problem the 3D finite element code has been developed for computing the stress-strain state in the elastoplastic medium near a borehole. The accuracy of the results, obtained due to the application of the finite element technique, can be affected by various numerical effects. Since the theory of plasticity assumes infinitesimal load increments, errors associated with finite increments are almost inevitable. The accuracy of the numerical solution can be verified by comparing the numerical results with the analytical solutions. Elasto-plastic analytical solutions [1], [2] stand out among others because they are the only ones among many others, mentioned in the cited monographs, that consider analytical solutions under conditions of non-hydrostatic loading.</p><p>In this study, the numerical and analytical solutions were verified and relative errors were calculated for different loading paths. It turned out, for example, that Galin’s analytical solution works well not only in the field of its applicability, but also outside of it, despite different errors. This work discusses questions related to the influence of the increment of the applied load on the structure of a stationary elasto-plastic solution, including in the case of the formation of zones of localized plastic deformation. The issue of the appearance of shear bands zones is also considered: these bands develop directly around the hole under certain boundary conditions or gradually grow out of the zones of elliptical plastic deformation.</p><p>The first, third and fifth authors acknowledge support of research by Geosteering technologies company within the scope of Geonaft project sponsored by Skolkovo foundation, Russia.</p><p>The second and fourth authors acknowledge support of research by Government of Russian Federation under grant 2019-220-07-9139.</p><p><strong>REFERENCES</strong></p><p>[1] Detournay, E. (1986). An approximate statical solution of the elastoplastic interface for the problem of Galin with a cohesive-frictional material. International Journal of Solids and Structures, 22(12), 1435–1454.</p><p>[2] Galin, L.A. (1946). Plane elastoplastic problem. Applied Mathematics and Mechanics, 10 (3), 365–386.</p>

Remaining Collapse Capacity of Corroded Pipelines

2011 ◽  
Author(s):  
Qishi Chen ◽  
Mark Marley ◽  
Joe Zhou
Keyword(s):  
Experimental Data ◽  
Finite Element ◽  
Wall Thickness ◽  
Numerical Models ◽  
Substantial Reduction ◽  
Assessment Method ◽  
Full Scale ◽  
Finite Element Models ◽  
Pipe Material ◽  
Corrosion Defects

It is known that, for given pipe material and diameter, collapse capacity of a plain pipe subjected to external pressure is proportional to the second or third power of wall thickness. In lieu of sophisticated numerical models and experimental data, conservative approaches such as those in which thickness losses at corrosion defects are extended to the entire circumference have been adopted in practices to assess the collapse resistance of corroded pipes. This reduced wall thickness is then used in the design equation of plain pipe to predict remaining collapse capacity. Such conservative assumptions result in substantial reduction of collapse capacity for pipelines with localized corrosion defects. During the course of a multiple-year PRCI research project, results of full-scale collapse tests and three-dimensional finite element analysis demonstrated that the reduction of collapse capacity was less than 10% for defects with a depth of 50% wall thickness, an axial length of one diameter and a circumferential width of half a diameter. These findings illustrated that the actual collapse capacity of corroded pipes is significantly higher than that estimated according to the conservative assumptions. This paper presents the development of a reliability-based, practical assessment method that allows remaining collapse capacity of corroded pipelines be determined based on defect size data obtained from in-line inspections. Work involved included characterization of corrosion defects, full-scale collapse tests, validation of finite element models using experimental data, analysis of parametric cases using finite element models, development of empirical equation based on experimental and numerical results, and calibration of partial safety factors which addressed the uncertainties associated with model error, load variation, and sizing inaccuracy of corrosion defects. Practical implications of the proposed assessment method were evaluated based on selected examples.

Crack in Corrosion Defect Assessment in Transmission Pipelines

2013 ◽  
Vol 135 (2) ◽  
Author(s):  
A. Hosseini ◽  
D. Cronin ◽  
A. Plumtree
Keyword(s):  
Crack Depth ◽  
Evaluation Criteria ◽  
Average Error ◽  
Failure Behavior ◽  
Pipe Material ◽  
Line Pipe ◽  
Collapse Pressure ◽  
Defect Assessment ◽  
Level 3 ◽  
Corrosion Defects

Cracks may occur coincident with corrosion representing a new hybrid defect in gas and oil pipelines known as crack in corrosion (CIC) that is not directly addressed in the current codes or assessment methods. Hence, there is a need to provide an assessment of CIC and evaluate the line integrity, as well as identify the requirements for defect repair or line hydrotest. An experimental investigation was undertaken to evaluate the collapse pressures of lines containing corrosion, cracks, or (CIC) defects in a typical line pipe (API 5L Grade X52, 508 mm diameter, 5.7 mm wall thickness). The mechanical properties of the pipe were measured using tensile, Charpy, and J-testing for use in applying evaluation criteria. Rupture tests were undertaken on end-capped sections containing uniform depth, finite length corrosion, cracks, or CIC defects. Failure occurred by plastic collapse and ductile tearing for the corrosion defects, cracks, and CIC geometries tested. For the corrosion defects, the corroded pipe strength (CPS) method provided the most accurate results (13% conservative on average). The API 579 (level 3 failure assessment diagram (FAD), method D) provided the least conservative collapse pressure predictions for the cracks with an average error of 20%. The CIC collapse pressures were bounded by those of a long corrosion groove (upper bound) and a long crack (lower bound), with collapse dominated by the crack when the crack depth was significant. Application of API 579 to the CIC provided collapse pressure predictions that were 18% conservative. Sixteen rupture tests were successfully completed investigating the failure behavior of longitudinally oriented corrosion, crack, and CIC. The pipe material was characterized and these properties were used to predict the collapse pressure of the defects using current methods. Existing methods for corrosion (CPS) and cracks (API 579, level 3, method D) gave conservative collapse pressure predictions. The collapse pressures for the CIC were bounded by those of a long corrosion groove and a long crack, with collapse dominated by the crack when the crack depth was significant. CIC failure behavior was determined by the crack to corrosion depth ratio, total defect depth and its profile. The results showed that the failure pressures for CIC were reduced when their equivalent depths were similar to those of corrosion and using crack evaluation techniques provided an approximate collapse pressure.

Probabilistic Approach for Reliability Estimation of Corroded Pipelines

2006 ◽  
Vol 306-308 ◽  
pp. 411-416
Author(s):  
Ouk Sub Lee ◽  
Dong Hyeok Kim ◽  
No Hoon Myoung ◽  
Si Won Hwang
Keyword(s):  
Failure Probability ◽  
Good Condition ◽  
Probabilistic Approach ◽  
Reliability Estimation ◽  
Operating Pressure ◽  
Pipe Material ◽  
Buried Pipelines ◽  
Safety Level ◽  
Reliability Method ◽  
Corrosion Defects

Pipelines widely used for the transportation of varying fluids from one place to another should be maintained in good condition to avoid, if possible, the occurrence of corrosion in pipelines to keep its reliability in terms of fracture and damage. The reliability of buried pipelines with corrosion defects is estimated using the failure probability. The FORM (first order reliability method) is utilized to estimate the failure probability of buried pipeline with various formulas for external stress in pipe and three different corrosion models. In this paper, it is recognized that the failure probability increases not only with increasing exposure time, operating pressure and diameter of pipe but also with decreasing wall thickness and yield stress of pipe material in three different corrosion models. And the effects of the scattering of random variables regarding reliability of pipelines on failure probability are investigated, systematically. Furthermore, the target safety level is used to determine the level of safe of corroded pipeline and the effects of varying boundary conditions on target safety level are also estimated.

On the Characterization of Strain-Hardening in Plasticity

1981 ◽  
Vol 48 (2) ◽  
pp. 285-296 ◽  
Author(s):  
J. Casey ◽  
P. M. Naghdi
Keyword(s):  
Strain Hardening ◽  
Plastic Behavior ◽  
Hardening Behavior ◽  
Perfectly Plastic ◽  
Plastic Materials ◽  
Space Formulation ◽  
Elastic Plastic Materials ◽  
Strain Hardening Behavior ◽  
Strain Space

In the context of a purely mechanical, rate-type theory of elastic-plastic materials and utilizing a strain space formulation introduced in [1], this paper is concerned mainly with developments pertaining to strain-hardening behavior consisting of three distinct types of material response, namely, hardening, softening, and perfectly plastic behavior. It is shown that such strain-hardening behavior may be characterized by a rate-independent quotient of quantities occurring in the loading criteria of strain space and the corresponding loading conditions of stress space. With the use of special constitutive equations, the predictive capability of the results obtained are illustrated for strain-hardening response and saturation hardening in a uniaxial tension test.

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