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• A-HNTs incorporated composite significantly reduced the moisture absorption rate. • Before moisture absorption, composite with A-HNTs exhibited higher flexural properties. • After moisture absorption composite with A-HNTs showed better retention than without A-HNTs. • Pipes with A-HNTs had higher stiffness before and after moisture absorption and after drying. • The A3 and E2A1 structures identifies as the most advantageous for industrial applications. The carbon fiber-reinforced polymer (CFRP) pipes are extensively used in various industrial sectors and are routinely exposed to diverse environmental conditions, making it imperative to enhance their performance and durability. To address this need, our study investigates the effects of incorporating amorphous halloysite nanotubes (A-HNTs) in different layers of five distinct layer arrangements on the bending and pipe stiffness properties of interleaved CFRP flat (F) and cylindrical (C) structures under various environmental conditions. Notably, the maximum moisture absorption rate of carbon/epoxy composites (A3), encompassing all layers of epoxy modified with A-HNTs, was 190 % lower than that of carbon/epoxy (E3) composites containing unmodified epoxy resin in all layers. Furthermore, F(A3) exhibited the highest flexural strength at 3141 MPa among all composites tested. A-HNTs significantly improved pipe stiffness, with C(A3) exhibiting remarkable stiffness enhancements of 314 % after moisture absorption and 268 % after drying compared to C(E3). The composite C(E2A1), which included a bottom layer of epoxy modified with A-HNTs, also demonstrated significant stiffness enhancements of 308 % after moisture exposure and 290 % after drying, compared to C(E3). Consequently, we recommend the use of A3 and E2A1 composites for industrial applications. [ABSTRACT FROM AUTHOR]

Pipe beams are considered under the action of bending. In case of elastic material, an analytical model of a one-dimensional beam is introduced, where the internal constraint between ovalization and bending curvature is deduced from mechanical considerations. Then, the softening moment-curvature relationship, able to describe the Brazier effect, is evaluated applying equilibrium equations in the nonlinear field. The same model is extended to the case where a structural foam is present as core of the pipe. The contribution of the core is analyzed in terms of its action in preventing instability phenomena. Finally, a model of lumped ovalization is discussed. [ABSTRACT FROM AUTHOR]

The paper focuses on tight fit pipe (TFP) wrinkling in rotary-draw bending (RDB), where TFP is a double-walled pipe. To this end, a corrosion-resistant alloy liner is fitted inside an outer carbon steel pipe through a thermal-hydraulic manufacturing process. A 3D elastic–plastic finite element (FE) model (the dynamic explicit FEM code ABAQUS/Explicit) is developed in this study. This model simulates the manufacturing process in the first step of the analysis and proceeds in the rotary-draw bending analysis of the lined pipe. Then, in the third step, the springback of the two-layer pipe is analyzed. This integrated three-stage process considers geometric nonlinearities, geometric and thickness imperfections, inelastic material behavior, and contact between the two pipes. Contact pressure during the process in the presence of various imperfections is monitored by the histogram to predict wrinkling. Furthermore, the best bending angle, with minimum possibility of wrinkling in the inner pipe, is obtained by these histograms. ABAQUS scripting via the Python programming language is used to study the effect of various imperfections on RDB. Numerical results on imperfection sensitivity demonstrate the significant influence of imperfections' amplitude on liner wrinkling. The ovality and thinning of the lined pipe via bending angle were investigated. By comparing the experimental results with those of the simulation, an appropriate agreement is observed. • The bending of Tight Fit Pipe (TFP) is investigated. • In this study, a 3D elastic–plastic FEM model is developed. • This integrated three-stage consider geometric nonlinearities, geometric and thickness imperfections, inelastic. • To prediction of wrinkling, contact pressure during the process in the presence of various imperfections is monitored by the histogram. • Numerical results on imperfection sensitivity demonstrate the significant influence of amplitude of imperfections on liner wrinkling. [ABSTRACT FROM AUTHOR]

This paper is dedicated to providing a detailed plastic collapse load analysis for un-cracked and circumferential through-wall cracked pipe bends under torsion moment by three dimensional FE methods considering geometric nonlinearity. For un-cracked pipe bends results show that radius-to-thickness is the main factors affecting the plastic collapse load. For cracked pipe bends the weakening factor decreases with increasing crack length, and the decreasing rate exhibits three typical stages which performs a similar trend with that in bending case. Although the weakening factor in plastic collapse load shows the similar variation based on geometric nonlinearity with that based on geometric linearity change, the limit load solutions based on geometric linearity fail to be used in prediction for torsion load based on geometric nonlinearity. So estimating limit load solutions by FE method are proposed, which shows a better choice compared with the past solutions. Furthermore the effect of yield strain is considered with the normalized parameter proposed to represent this weakening effect of yield strain on torsion moment. Results show that pipe parameters bend radius-to-radius and crack length have little impact on the weakening parameter, however radius-to-thickness have an obvious impact on the weakening parameter, which increases with decreasing weakening parameter. Results also show that radius-to-thickness has a great impact on the ovality deformation, while bend radius-to-radius hasn't. Therefore geometry effect is significant for a high yield strain value and a high radius-to-thickness value. [ABSTRACT FROM AUTHOR]

A comparative evaluation of limit moments based on small displacement and collapse moments based on large displacement for structurally distorted throughwall circumferentially cracked pipe bends, under in-plane closing bending were carried out using finite element analysis. The moments were obtained employing the twice-elastic-slope method. Results indicate the influence of thinning is minimal whereas the effects of ovality on both limit and collapse moments for the cases considered are significant and therefore thinning need not be considered in the analysis. Moreover determination of collapse moments is preferred when ovality is incorporated in the analysis of pipe bends with the geometries considered. [ABSTRACT FROM AUTHOR]

The pipelines for oil and gas transportation are generally laid along a straight route to avoid the complexity of pipe bending. However, changing of pipe alignment is sometimes unavoidable where a straight pipeline is mechanically bent, or two straight pipelines are connecting using a suitable pipe bend/elbow. In this study, the burst pressure of corroded and uncorroded pipe bends was investigated using finite element analysis. The study shows that the pipe bend reduces the burst pressure that depends extensively on the radius of the bend. A parametric study was conducted to identify the parameters affecting the burst pressure of the pipe bend. The parameters investigated included bend radius, bend angle, pipe dimensions, corrosion dimensions, location of corrosion, and the grade of the steel. Corrosion at the intrados of the bend was found to have the most adverse effect on the burst pressure of bend for pipes with lower bend radii. The ratio of the burst pressure of the pipe bend to the burst pressure of corresponding straight pipes depends on the bend radius and steel grade and is almost independent of the pipe and corrosion dimensions. This ratio can be used to assess the burst pressure of a pipe bend using the burst pressure of the corresponding straight pipe. However, for a bend radius greater than three times the pipe diameter, the burst pressure of pipe bend is almost the same as the burst pressure of the corresponding straight pipe. • The burst pressures of intact and corroded pipe bends were investigated using finite element analysis. • Bend radius is found to affect the burst pressure more significantly than the bend angle. • Corrosion at the intrados position has the most adverse effect on the burst pressure. • The Burst pressure ratio can be used to calculate the burst pressure of pipe bend from the burst pressure of straight pipe. • Burst pressure model specific to steel grade should be used for the fitness-for-purpose assessment. [ABSTRACT FROM AUTHOR]

A family of shell finite elements is developed for the geometrically nonlinear analysis of pipe bends. The constitutive description follows the Saint-Venant-Kirchhoff model. The first Piola–Kirchhoff stress and the conjugate gradient of the virtual displacement fields are adopted within the framework of the virtual work principle. Three C 1 continuous schemes are used to interpolate the displacement fields in the longitudinal direction while Fourier series are used for circumferential interpolation. Eigenvalue analyses are conducted to assess the ability of the elements to represent rigid body motion. Comparisons with other shell and elbow models demonstrate the accuracy and versatility of the formulation. • Finite elements are formulated for geometric nonlinear analysis of pipe bends. • Solution adopts First Piola–Kirchhoff stress within the virtual work principle. • Eigenvalue analyses assess the ability of elements to capture rigid body motion. • The formulation properly tackles the effect of follower loads (e.g., pressure). • The formulation accurately captures the nonlinear response. [ABSTRACT FROM AUTHOR]

Pipe elbows, also known as pipe bends, are important components of a piping system. These curved elements are very flexible when compared to their straight counterparts, and are often responsible for reducing the reaction forces and moments within the piping system. However, due to large deformations, the elbows are more likely to exceed their stress limits. The effect of in-plane bending on plastic limit loads of Functionally Graded (FG) pipe bends is presented using three-dimensional non-linear finite element analysis and a micromechanical constitutive model. The effective properties of the material are estimated by the Mori–Tanaka homogenization scheme and the TTO plasticity model. The analysis was carried out for different loading cases, geometries and volume fraction distribution. The results showed that an FG elbow has a very distinct behavior comparatively to a similar homogeneous elbow made out of metal, specially in terms of limit moments and stress distribution. Finally, an analytical model to estimate the limit moment of FG elbows is presented. • Functionally Graded pipe elbows provide wear resistance and ductility without the associated interfacial problems. • The volume fraction distribution of ceramic inclusions was found to play a major role on the overall behavior of FGM pipes. • Micromechanical Elastoplastic models can be easily employed to simulate the behavior of FGM metal-matrix pipe elements. • The volume fraction distribution of ceramic inclusions plays a major role on the overall bending behavior of FGM pipe elbows. • A predicting equation for bending of FGM pipes was developed for limit bending moments. [ABSTRACT FROM AUTHOR]

Steel wire reinforced thermoplastic pipe (PSP) is a polymer–matrix composite pipe of excellent quality, and it shows great potential in different industries. In this study, bearing capacity of PSP under combined internal pressure and bending moment at various temperatures was investigated. Tests were conducted through a specifically designed mechanical testing system, and the temperatures varied from 20 °C to 60 °C. With a pre-set internal pressure of 2.8 MPa, bending moment was applied until failure. It was found that the fracture of steel wires leads to the failure of pipe, and higher temperature has a negative effect on the pipes' bending capacity. A finite element (FE) model was subsequently established to analyze the failure process and influence factors of PSP under combined loads. • A testing system for composite pipes under complex loads was developed. • Failure modes of SRTP under combined loads at different temperatures were studied. • A experimentally verified FEA model was used to analyze key factors in SRTP failure. [ABSTRACT FROM AUTHOR]

Abstract: An alternative formulation to current meshes dealing with finite shell elements is presented to solve the problem of stress analysis of curved pipes subjected to in-plane bending forces. The solution is based on finite curved elements, where displacements are defined from a total set of trigonometric functions or a fifth-order polynomial, combined with Fourier series. Global shell displacements are achieved through the one associated with curved arch bending and the other referred to the toroidal thin-walled shell distortion. Beam-type displacement and in-plane rotation are uncoupled and separately formulated, using trigonometric shape functions, as in Timoshenko or Mindlin beam theory. To build up the solution, a simple deformation model was adopted, based on the semi-membrane concept of the doubly curved shells behaviour. Several studies are presented and compared with experimental and numerical analyses reported by other authors. [Copyright &y& Elsevier]

Abstract: An experimental investigation was conducted to compare the crush characteristics and energy absorption capacity of AA6061-T6 aluminum alloy extrusions with centrally located through-hole discontinuities. Three different types of geometrical discontinuities, namely, circular, slotted and elliptical holes were fabricated into AA6061-T6 extrusions which had a length of 200mm, nominal side width of 38.1mm and wall thickness of 3.15mm. Furthermore, three different major axis lengths (7.14, 10.72, and 14.29mm) and three different aspect ratios (1.33, 2.0, and 3.0) of the slotted and elliptical discontinuities were considered. It was found that by introducing crush initiators into the structural members, a splitting and cutting deformation mode was generated rather than global bending deformation which was observed for specimens without any discontinuities. The peak crush load was reduced by incorporating the through-hole crush initiators within a range of 5.2–18.7%, and total energy absorption was increased within a range of 26.6–74.6%. The most significant improvement was noted in the crush force efficiency, which was increased within the range of 54.5–95.8%. For specimens with discontinuities which had a major axis length of 7.14mm the peak crush load and total energy absorption was independent of initiator geometry and aspect ratio. However, for specimens which had discontinuities with a major axis length of 10.72 and 14.29mm and an aspect ratio of 3, a geometrical influence on the peak crush load and total energy absorption was apparent. [Copyright &y& Elsevier]

This paper presents the dynamic analysis extension of the Generalized Beam Theory (GBT) formulation developed in [1] for curved thin-walled pipes. The new proposed dynamic curved GBT element formulation goes beyond the current GBT's analysis of straight pipes, not only concerning the coupling and behavior of pipe bends or toroidal shells, but also concerning the effects of the transverse shear modes. In the preceding paper, the stresses and the deformations of a pipe bend under static conditions have been determined through the potential energy formulation for different loading and support conditions. In this paper, the formulation of the kinetic energy is presented to determine the inertia of the GBT element. The consistent element mass matrix derived from the GBT dynamic formulation involves the coupling of certain types of GBT deformation modes resembling that of the element stiffness matrix. Here, to illustrate the application and capabilities of the developed GBT formulation, numerical examples concerning undamped free vibration analysis of truncated and closed toroidal shells with different support conditions are considered involving a combination and coupling of bending, warping, torsional, axisymmetric and local deformation modes. For the purpose of validation, these examples are compared with refined shell finite element models. • Dynamic GBT formulation of toroidal shells is presented and validated. • Coupled GBT deformation modes are identified. • Numerical examples of truncated and closed toroidal shells are presented. • Modal Assurance Criterion (MAC) analysis is used to validate the mode shapes. [ABSTRACT FROM AUTHOR]

Sandwich pipe (SP), composed of two concentrically steel tubes with a strain-hardening cementitious composite (SHCC) filling core, is a new concept designed for oil and gas transportation in deep waters. Bending is a primary loading condition for the SP during the installation process. There is currently a lack of research on SPs' bending capacity, considering the actual interlayer behavior. The extreme adhesion conditions of fully bounded and unbounded layers have been commonly adopted in numerical simulations. This paper aims to study the actual interlayer behavior through push-out and self-stress tests and proposes an SP numerical model with a bond-slip layer, based on the finite element method. The results from experimental tests for bending on a rigid surface to simulate the reeling installation method are correlated with the results from the finite element model, presenting good agreement. A parametric study is then performed to investigate the influence of geometric parameters and the interlayer bond behavior on the ultimate bending strength. • Push-out and self-stress tests to study the actual interlayer behavior of sandwich pipes are presented. • A numerical model with a bond-slip layer for sandwich pipe is proposed. • Full-scale sandwich pipes bending tests are presented. • A correlation study between the experimental and numerical results is performed. • Influence of geometric parameters and initial ovality on the ultimate bending moments of sandwich pipe are analyzed. [ABSTRACT FROM AUTHOR]

In this paper, the linear Generalized Beam Theory (GBT) is formulated for stress and deformation analysis of curved thin-walled circular pipes. In comparison to the analysis of straight pipes, the analysis of pipe bends is a complex problem due to the strong coupling effect of the longitudinal bending, warping and the cross-sectional ovalization. GBT is a beam theory especially formulated for thin-walled sections with the capacity of determining the cross-sectional deformation through the combination of a set of predetermined cross-sectional deformation modes. This nature of GBT makes it suitable to precisely identify and determine possible couplings between the considered GBT deformation modes and to analyze the behavior of pipe bends with high accuracy and computational efficiency. The formulation presented in this paper is based on Kirchhoff's thin-plate assumption with consideration of additional shear deformation modes to overcome null transverse extension and shear membrane strain assumptions of classical GBT formulations. Here, to illustrate the application and capabilities of the developed GBT formulation, a set of numerical examples with in-plane, out-of-plane and pressure loading conditions involving a combination and coupling of bending, warping, torsional, axisymmetric and local deformations are presented. For the purpose of validation, these examples are compared with refined shell finite element models in both displacement and stress fields. • Linear GBT formulation of circular pipe bends is presented and validated. • Numerical examples are presented considering various loading and boundary conditions. • GBT's high accuracy and computational efficiency are demonstrated. • The effect of the Poisson ratio is investigated in circular pipe bends. • The relationship between GBT's modes and the bend curvature is presented. [ABSTRACT FROM AUTHOR]

The ratcheting behavior of pressurized corroded straight pipe subjected to cyclic bending is investigated using Chaboche model in the paper. The effects of defect length, depth and width and internal pressure on ratcheting strain are studied. The results show that the ratcheting strain increases with the increase of defect length L / D , depth H / T , circumferential length and internal pressure. Moreover, in order to analyze the effect of defect size on ratcheting strain of corroded straight pipe, calculation schemas are established according to orthogonal design method (ODM). Finally, dimensionless relations of both circumferential and longitudinal ratcheting strains to defect length, depth, width and internal pressure are established based on the multiple regression method. • Ratcheting behavior is studied on pressurized corroded pipe under bending load. • Ratcheting strain of pipe with different defect sizes is simulated by Chaboche model. • Dimensionless relations of ratcheting strain and defect sizes were obtained. [ABSTRACT FROM AUTHOR]

The fabrication of pipe bends using rotary pipe bending (RPB) process results in geometrical imperfections as described by cross-sectional ovality and wall thickness variations which affect the pipe bends performance during service. Previous studies whether ignores these imperfections (Ideal pipe bend (IB)) or assume these imperfections in their analysis (Assumed shape bend (AS)). The objective of the present work is to investigate, using non-linear finite element analysis, the effect of the residual stresses and the presence of the inherited geometrical imperfections (low ovality) obtained from RPB process of 90° pipe bends on their load carrying capacities as compared with the IB and AS models. RPB process with basic tooling configuration is first simulated to obtain the as-fabricated 90° pipe bend. The results of this step were verified against published experimental results and analytical solutions, and compensated for springback. The pipe bend was then subjected to different combinations of loads (in-plane moment and internal pressure) to construct a comparative limit load diagram. Within the scope of our study, results have shown that the presence of the residual stresses remarkably reduces the pipe bend load-carrying capacity. IB model results in non-conservative results as geometrical imperfections lower the load carrying capacity of the pipe bend, while the AS model has been found to be invalid for cases where a mandrel is used in RPB process. • Limit loads for as-fabricated, annealed, ideal, and idealized pipe bends are compared. • Geometrical imperfections lower the limit loads of the As-Fabricated pipe bend with low ovality. • Ideal pipe bend model provides non-conservative results for limit loads. • High residual stresses in pipe bends made with mandrels limit their load carrying capacity. [ABSTRACT FROM AUTHOR]

Damage caused by corrosion is one of the main factors that diminish the performance of thin-walled structures such as pipelines. Using experimental and numerical methods, this study investigated the effects of corrosion depth and corrosion shape on the performance of corroded thin-walled steel pipes when subject to combined internal pressure and 4-point bending load. The effect of corrosion depth was studied using three API 5 L X52 grade pipe specimens with a nominal diameter of 8-inches (203 mm), and the effect of corrosion shape was investigated by testing five API 5 L X46 specimens with a nominal diameter of 6-inches (152 mm), containing different corrosion shapes. It was found that increasing the corrosion depth drastically decreases the bending capacity of the corroded specimens. Also, it was observed that the specimens with circular and square corrosion shapes exhibited the same bending behaviour, and extending the corrosion along the circumferential direction of the pipe wall caused the most negative effect on the bending behaviour of the specimen. • This study examined the effect of corrosion depth and shape on the performance of pipes under bending and internal pressure. • Increasing the corrosion depth drastically decreases the bending capacity of pressurized, thin-walled steel pipes. • Internal pressure of up to 0.6p y did not significantly impact the ultimate load-carrying capacity of the corroded pipes. • uThe square and circular corrosion shapes had the same influence on the load-displacement behaviour of the corroded specimens. • Corrosion defect was more harmful when extended in the circumferential direction as compared to the longitudinal direction. [ABSTRACT FROM AUTHOR]