An Analytical Treatment of Buckling and Instability of Tensile Armors in Flexible Pipes

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Svein Sævik ◽  
Mats J. Thorsen
Keyword(s):  
Differential Equation ◽  
Test Data ◽  
Local Buckling ◽  
Analytical Models ◽  
Ultimate Capacity ◽  
Analytical Treatment ◽  
Alternative Models ◽  
Outer Sheath ◽  
Flexible Pipes ◽  
Transverse Stability

The present paper addresses aspects related to local buckling and instability of tensile armors in flexible pipes. Analytical models for evaluating the tensile armor buckling capacity in both transverse (radial and lateral) directions are presented based on formulating the linearized differential equation describing transverse stability of the thin curved wire assuming no friction. Then analytical models for the ultimate capacity of the outer sheath and antibuckling tape are formulated and a combined criterion for radial instability is proposed based on considering radial buckling of the tensile armor, wire yield failure, and the ultimate capacity of the outer sheath and tape. Thereafter, a study is performed comparing the proposed models with test data and alternative models available in the literature.

scholarly journals Interactive Buckling of Q420 Welded Circular Tubes under Axial Compression

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Bin Huang ◽  
Zhou Che Hong
Keyword(s):  
Residual Stresses ◽  
Axial Compression ◽  
Test Data ◽  
Local Buckling ◽  
Ultimate Capacity ◽  
Geometric Imperfection ◽  
Circular Tubes ◽  
Limit Value ◽  
Buckling Resistance ◽  
Interactive Buckling

Finite element models (FE models) of high-strength steel Q420 (yield strength 420 MPa) circular tubes considering residual stresses and local and overall geometric imperfections were established and verified against existing test data. Based on parameter analysis, it was derived that the reduction of ultimate capacity resulting from residual stresses was up to 11.8%. When slenderness ratio was larger than 25, the effect of overall geometric imperfection played a major role compared with that of local geometric imperfection, which resulted in the reduction of the ultimate capacity of about 11.5%. Through tracking the failure process, it was found that, in the initial stage of loading, the deformation of columns mainly presents overall bending. When the load increased near the ultimate load, local buckling occurred and the bearing capacity decreased rapidly. The D/t limit value 27 was determined for preventing the local buckling, and the overall slenderness λl limit value 40 was proposed to distinguish whether local buckling occurs. Based on the FEM result and test data, the applicability of ASCE48-05 and AS4100 for local buckling resistance was evaluated. Continuing the result of stub columns, curve a in GB50017-2017 and in Eurocode 3 of the overall buckling factor φ was proposed to be used in EWM and DSM for estimating the interactive buckling resistance of circular tubes of Q420 under axial compression.

Differential Equation for Evaluating Transverse Buckling Behavior of Tensile Armour Wires

2014 ◽  
Author(s):  
Svein Sævik ◽  
Guomin Ji
Keyword(s):  
Differential Equation ◽  
Numerical Study ◽  
Failure Criteria ◽  
Fe Analysis ◽  
Design Criteria ◽  
Transverse Tensile ◽  
Flexible Pipes ◽  
Buckling Behavior ◽  
Transverse Stability ◽  
Bending Behaviour

The present paper addresses aspects related to transverse tensile armour buckling in flexible pipes. An analytical model for evaluating the tensile armour buckling capacity is presented based on formulating the linearised differential equation describing the transverse stability of the thin curved wire assuming no friction. This is followed by a numerical study based on FE analysis to evaluate the extra capacity from friction during cyclic bending behaviour and where the yield stress is used as the failure criteria. The results is then compared to test data and a design criteria for transverse tensile armour buckling proposed.

scholarly journals Experimental Study on the Effect of Heel Plate Length on the Structural Integrity of Cold-formed Steel Roof Trusses

2018 ◽  
Vol 65 ◽  
pp. 08010
Author(s):  
Je Chenn Gan ◽  
Jee Hock Lim ◽  
Siong Kang Lim ◽  
Horng Sheng Lin
Keyword(s):  
Ultimate Load ◽  
Structural Integrity ◽  
Load Capacity ◽  
Local Buckling ◽  
Ultimate Capacity ◽  
Ultimate Load Capacity ◽  
Plate Length ◽  
Roof Truss ◽  
Cold Formed Steel ◽  
Structural Failures

Applications of Cold-Formed Steel (CFS) are widely used in buildings, machinery and etc. Many researchers began the research of CFS as a roof truss system. It is required to increase the knowledge of the configurations of CFS roof trusses due to the uncertainty of the structural failures regarding the materials and rigidity of joints. The objective of this research is to investigate the effect of heel plate length to the ultimate load capacity of CFS roof truss system. Three different lengths of heel plate specimens were fabricated and subjected to concentrated loads until failure. The highest ultimate capacity for the experiment was 30 kN. The results showed that the increment of the length of the heel plate had slightly increased the ultimate capacity and strain. The increment of the length of the heel plate had increased the deflection of the bottom chords but decreased the deflection of the top chords. Local buckling of top chords adjacent to the heel plate was the primary failure mode for all the heel plate specimens.

Prediction and Qualification of Radial Birdcage and Lateral Buckling of Flexible Pipes in Deepwater Applications

2015 ◽  
Author(s):  
Linfa Zhu ◽  
Zhimin Tan ◽  
Victor Pinheiro Pupo Nogueira ◽  
Jian Liu ◽  
Judimar Clevelario
Keyword(s):  
Failure Modes ◽  
Local Buckling ◽  
External Pressure ◽  
Design Guidelines ◽  
Prediction Theory ◽  
Flexible Pipe ◽  
Lateral Buckling ◽  
Operation Conditions ◽  
Flexible Pipes ◽  
Compressive Loads

Increasing oil exploitation in deepwater regions is driving the R&D of flexible pipes which are subjected to high external pressure loads from the hydrostatic head during their installation and operation. One of the challenges of flexible pipe design for such applications is to overcome the local buckling failure modes of tensile armor layers due to the combination of high external pressure, compressive loads and pipe curvature. This paper presents the latest progress in local buckling behavior prediction theory and the qualification process of flexible pipes. First, the mechanisms of two types of buckling behaviors, radial birdcage buckling and lateral buckling, are described. For each failure mode, the analytical buckling prediction theory is presented and the driving parameters are discussed. As part of the qualification process, the ability to resist radial birdcage and lateral buckling must be demonstrated. Suitable test protocols are required to represent the installation and operation conditions for the intended applications by deep immersion performance (DIP) tests. Several flexible pipes were designed based on radial birdcage and lateral buckling prediction theory, and pipe samples were manufactured using industrial production facilities for DIP tests. The results clearly show that flexible pipes following current design guidelines are suitable for deepwater applications. An alternative in-air rig was developed to simulate the DIP tests in a controlled laboratory environment to further validate the model prediction as a continuous development.

Polyamide 11: A High Tenacity Thermoplastic, Its Material Properties and the Influence of Ageing in Offshore Conditions

2002 ◽  
Author(s):  
Michael Werth ◽  
Gilles Hochstetter ◽  
Patrick Dang ◽  
Nathalie Chedozeau
Keyword(s):  
Material Properties ◽  
Mechanical Response ◽  
Sea Water ◽  
Flexible Pipe ◽  
Polyamide 11 ◽  
Water Ingress ◽  
Outer Sheath ◽  
Flexible Pipes ◽  
Operating Limits ◽  
Sheath Material

Polyamide 11 is a key material in the fabrication of offshore flexible pipes. It is mainly used as the flexible pressure layer assuring the impermeability of the fluid and gas carrying flexible pipe. A further important use is as outer sheath material where it protects efficiently the metal strip structure from sea water ingress even in highly dynamic applications. Given these important functions of polyamide 11 the knowledge of its precise material properties is essential for the design and the operating limits of flexible pipes. This paper aims to give a detailed understanding of the scope of the material properties such as fracture toughness, fatigue resistance and the mechanical response function. In a further step the influence of ageing on these properties is outlined with the aid of aged model specimen studies.

Damping Characteristics of Fairings for Suppressing Vortex-Induced Vibrations

2004 ◽  
Author(s):  
Li Lee ◽  
Don W. Allen ◽  
Dean L. Henning ◽  
Doug McMullen
Keyword(s):  
Wave Attenuation ◽  
Analytical Models ◽  
Superposition Method ◽  
Test Configuration ◽  
Function Solution ◽  
Mode Superposition Method ◽  
Flexible Pipes ◽  
Vortex Induced Vibrations ◽  
Vibration Responses ◽  
Quantitative Manner

Vortex-induced vibration (VIV) tests have been performed on long, flexible pipes with fairings in sheared flows in a circular towing tank at prototype Reynolds numbers for production risers [1]. It is discovered that there existed strong attenuation of the vibration responses for the test configuration with fairings placed in the strong current zone, compared to the pipe configuration without any fairings. Wave attenuation is typical when waves travel in systems with dissipation. Strong attenuation is an indication of large damping. Additional pluck tests of pipes with fairings in still water were conducted to determine damping in the system in a quantitative manner. The results, though scattered, provide evidence on the level of damping that could exist in structures with fairings. Furthermore, analytical models based on a Green’s function solution and mode superposition method for a taut string were also used to complement experimental data. A range of damping values was considered to find the damping value for which the level of attenuation matched that of the experiments. It is found that this damping value is close to that from the tests.

Flow of Non-Newtonian Power-Law Fluids Through Porous Media

1979 ◽  
Vol 19 (03) ◽  
pp. 155-163 ◽  
Author(s):  
A.S. Odeh ◽  
H.T. Yang
Keyword(s):  
Differential Equation ◽  
Partial Differential Equation ◽  
Porous Media ◽  
Test Data ◽  
Power Law ◽  
Newtonian Fluids ◽  
Unsteady State ◽  
Partial Differential ◽  
State Flow ◽  
Power Law Fluids

Abstract The partial differential equation that describes the flow, of non-Newtonian, power-law, slightly compressible fluids in porous media is derived. An approximate solution, in closed form, is developed for the unsteady-state flow behavior and verified by. two different methods. Using the unsteady-state solution, a method for analyzing injection test data is formulated and used to analyze four injection tests. Theoretical results were used to derive steady-state equations of flow, equivalent transient drainage radius, and a method for analyzing isochronal test data. The theoretical fundamentals of the flow, of non-Newtonian power-law fluids in porous media are established. Introduction Non-Newtonian power-law fluids are those that obey the relation = constant. Here, is the viscosity, e is the shear rate at which the viscosity is measured, and n is a constant. Examples of such fluids are polymers. This paper establishes the theoretical foundation of the flow of such fluids in porous media. The partial differential equation describing this flow is derived and solved for unsteady-state flow. In addition, a method for interpreting isochronal tests and an equation for calculating the equivalent transient drainage radius are presented. The unsteady-state flow solution provides a method for interpreting flow tests (such as injection tests).Non-Newtonian power-law fluids are injected into the porous media for mobility control, necessitating a basic porous media for mobility control, necessitating a basic understanding of the flow behavior of such fluids in porous media. Several authors have studied the porous media. Several authors have studied the rheological properties of these fluids using linear flow experiments and standard viscometers. Van Poollen and Jargon presented a theoretical study of these fluids. They described the flow by the partial differential equation used for Newtonian fluids and accounted for the effect of shear rate on viscosity by varying the viscosity as a function of space. They solved the equation numerically using finite difference. The numerical results showed that the pressure behavior vs time differed from that for Newtonian fluids. However, no methods for analyzing flow-test data (such as injection tests) were offered. This probably was because of the lack of analytic solution normally required to understand the relationship among the variables.Recently, injectivity tests were conducted using a polysaccharide polymer (biopolymer). The data showed polysaccharide polymer (biopolymer). The data showed anomalies when analyzed using methods derived for Newtonian fluids. Some of these anomalies appeared to be fractures. However, when the methods of analysis developed here were applied, the anomalies disappeared. Field data for four injectivity tests are reported and used to illustrate our analysis methods. Theoretical Consideration General Consideration The partial differential equation describing the flow of a non-Newtonian, slightly compressible power-law fluid in porous media derived in Appendix A is ..........(1) where the symbols are defined in the nomenclature. JPT P. 155

Friction Behavior Between Epoxy and Flexible Pipes Armor Wires

2016 ◽  
Author(s):  
Diego A. Lorio ◽  
Facundo J. Wedekamper ◽  
Fabiano Bertoni ◽  
Facundo S. Lopéz ◽  
George C. Campello ◽  
...  
Keyword(s):  
Friction Coefficient ◽  
Contact Pressure ◽  
Normal Load ◽  
Surface Profile ◽  
Repeated Measurements ◽  
Analytical Models ◽  
Friction Coefficients ◽  
Wire Sample ◽  
Flexible Pipes ◽  
The Wire

The offshore industry has presented an increasing demand over the last few decades, requiring the production in deep water fields. The end fittings (EF) are critical points within the production system. Therefore, structural and fatigue analyses are essential in the EF design, making it necessary to know the stress distribution experienced by the armor wires along the EF. Numerical and analytical models are often used in order to assess the stress state. However, characteristics like geometries, materials and interactions must be previously known in order to apply these models. The purpose of this work was to analyze the arithmetic mean surface roughness (Ra) and to determine the friction coefficient (μ) for two types of armor wires when in contact with resin used to fill the EF. The resin used in the interaction with the armor wires was an epoxy filled with metallic particles. For the experimental analysis straight carbon steel armor wires with different cross-sections, typically used in 2.5″ and 8″ flexible pipes were used. Surface profile was obtained for each wire by repeated measurements along two lines over each surface. A total of three repetitions were performed in each measure line. Longitudinal roughness was determined through these profiles. Finally, friction coefficients were obtained experimentally by means of a device that allows to simulate the wire pullout and sliding process. In this device, two epoxy pads were put in contact with the surface of the analyzed wire sample, and rigid bodies in contact with the pads were used to ensure that the normal load applied is transmitted uniformly through the contact surface. The displacement rate, contact pressure between the surface of the wire and the epoxy resin pads, and axial force were recorded. The roughness in the longitudinal direction of the wires was analyzed through descriptive statistic and compared by Student’s “t” test. The highest values were obtained on wires with larger sections. This behavior is exposed on the results obtained for the friction coefficient as a function of the contact pressure. Friction coefficient for both wires was analyzed and compared using a Mann-Whitney U test. Both friction coefficients have a positive slope, indicating a small increase as the contact pressure raise. The significance value obtained for the means comparisons was p = 0.0001 and confirms that the average friction coefficient of the two wires are really different. Because of that, we conclude that is necessary to treat the EF project for different flexible pipes differentially.

Material Property Effects on Critical Buckling Strains in Energy Pipelines

2002 ◽  
Author(s):  
Alfred B. Dorey ◽  
David W. Murray ◽  
J. J. Roger Cheng
Keyword(s):  
Material Property ◽  
Parametric Study ◽  
Numerical Models ◽  
Local Buckling ◽  
Analytical Models ◽  
Basic Material ◽  
Line Pipe ◽  
Moment Capacity ◽  
Yield Plateau ◽  
Critical Buckling Strain

Investigations in the development of a predictive critical buckling strain equation have shown that the grade of the material is one of five fundamental non-dimensional parameters in determining the critical local buckling strain for line pipe under combined loads. Further to this, the shape of the material curve also plays a significant role in the resulting critical buckling strain. Over 50 full-scale test specimens have been tested at the University of Alberta and effective numerical finite element analytical models have been developed. A parametric study consisting of 170 analyses was performed using the numerical models and critical buckling strain equations were derived. One of the essential variables in the new equations is a function of the specimen’s material properties. The results indicate that the higher the grade of the material the lower the value of the critical buckling strain. Furthermore, the level of agreement between the new equations and the experimental data was found to be dependent on the shape of the material curve for the specimen. Experimentally, two basic material curve shapes were observed, namely: specimens with a “rounded” material curve through the yield strength and specimens with a material property that exhibited a distinct “yield plateau” or yield point. Comparison of the experimental and numeric data showed that the specimens that were fabricated from material with a distinct yield plateau had different critical buckling strains when compared to specimens tested with rounded material curves. A subsequent parametric study was undertaken to examine the effect that the different shaped material curves had on the local and global behaviour. The results of this subsidiary parametric study showed that the global moment capacity was essentially independent of the shape of the material curve (the ratio of the peak moment from the yield plateau material to the peak moment for the rounded material was 1.018). However, the local critical buckling strain was significantly lower for the specimens analyzed with the material that had the yield plateau (the ratio of the critical strains for the two different material curves was 0.710).

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