New Limit State Functions for Determining the Puncture Resistance to External Force

2002 ◽  
Author(s):  
Jianhui Liu ◽  
Andrew Francis
Keyword(s):  
Internal Pressure ◽  
Failure Mode ◽  
External Force ◽  
Maximum Stress ◽  
Limit State ◽  
Pipe Material ◽  
Stress Strain ◽  
Indentation Force ◽  
The Impact ◽  
Dent Depth

Traditionally, a key component of the design philosophy applied to high-pressure pipelines has been the stipulation that the nominal hoop stress is less than some fraction of the specified minimum yield strength (SMYS). However, more recently both designers and operators have recognised that whilst this approach generally leads to conservatively safe designs, there may be some situations in which the conservatism is not adequate. This has resulted in a move towards limit state, and structural reliability based, methods that address actual failure modes, and consequently the contributions to structural integrity of other factors in addition to stress. One such failure mode is the puncture of a pipeline wall due an external force. This situation can arise from the impact of excavating machinery for onshore pipelines or drop objects and anchors for offshore lines. A limit state function describing this failure mode is given in DNV guidelines No 13. However, this function does not take account of the internal pressure. In this paper the influence of pressure on the pipeline indentation is addressed using both theoretical and finite element analyses. A closed-form solution of force-deformation relationship based on a consideration of rigid-plastic deformation theory, that gives a good agreement with results from both FE analyses and experimental tests, is presented. The analytical results show that indentation force, and the maximum stress/strain, required to produce a given dent depth, increase with increasing internal pressure. However, the relationship between indentation force and maximum stress/strain is not sensitive to internal pressure. The analysis therefore shows that an indentation force criterion governed solely by the dent depth, such as that given in DNV guidelines No. 13, may be highly unconservative when the pressure in the pipeline is high. Consequently, a new local denting criterion for puncture of pressurised pipes, which is based the maximum acceptable strain of the pipe material, and thereby removes the above unconservatsim, has been proposed and is presented in this paper.

High Peak Strain on Pipeline Material During Reel-Lay: Acceptable or Not?

2016 ◽  
Author(s):  
Erwan Karjadi ◽  
Henk Smienk ◽  
Philippe Thibaux ◽  
Olav Aamlid
Keyword(s):  
Plastic Deformation ◽  
Limit State ◽  
High Peak ◽  
Homogeneous Material ◽  
Test Machine ◽  
Pipe Material ◽  
Peak Strain ◽  
Nominal Strain ◽  
Tension And Compression ◽  
The Impact

The nominal strain occurring during installation of a pipeline by the reeling method is expected to be limited to 2–3% strain. This is only true if the pipeline has a perfect geometry (diameter, thickness) and homogeneous material properties along its length, resulting in a uniform bending stiffness. There will however always be a stiffness mismatch at the joints between pipes. Different scenarios can be considered as the cause of this stiffness mismatch: differences in average wall thickness and average yield stress of two pipe joints welded together, counterbored/machined pipe ends or field joint coating for pipes with thick coating. To some extent these scenarios can initiate high peak strains in the pipeline material far above the level of the expected nominal strain, exceeding in some cases 5% strain. Questions which might arise are: Could this high peak strain occurrence be ignored?, or: What is the impact of the high peak strain on the performance of the material after reeling? This paper presents FEA results illustrating the concerns of the occurrence of large peak strains which can still be significant even after averaging these strains over the thickness as well as over a certain length of the pipe. The methodology of averaging strains, as proposed together with DNV GL, correlates the length of the averaging pipe section with the maximum length of the test specimen geometry as allowed when performing strain aging tests of specimens with high tension and compression strains. A series of cyclic plastic deformation tests with pre-strained specimens from 4% to 7% strain was performed with seamless pipe material, followed by the tensile, Charpy and hardness tests of strain aged samples. One of the challenges is the setup of the test machine to avoid buckling of specimens during high compression pre-straining. The results from material tests (tensile, hardness and Charpy) have been evaluated against the DNV-OS-F101 Supplementary requirement for plastic deformation (P). The consequences of material modification due to plastic strain is further discussed and evaluated referring to the DNV GL limit state design and criteria for pipeline installation after reeling as well as during the lifetime of the pipeline.

Responses of Submarine Pipelines to Impacts in Soft Clay

2016 ◽  
Author(s):  
Yi Wang ◽  
Jixiang Yue ◽  
Menglan Duan ◽  
Zhang Yu ◽  
Yi Zhao
Keyword(s):  
Internal Pressure ◽  
Soft Clay ◽  
Local Deformation ◽  
Offshore Pipelines ◽  
Environmental Consequences ◽  
Deformation And Fracture ◽  
Subsea Pipelines ◽  
The Impact ◽  
Impact Damages ◽  
Dent Depth

Subsea pipelines have been widely used to transfer oil from platforms to the mainland near harbor anchorage zone, and they become increasingly susceptible to risks stemming from dropped object impact damages. The impact from dropped objects may lead to local deformation and fracture in the pipeline and vast economic and environmental consequences. In this research, the responses of continuously supported offshore pipelines subjected to transverse impacts caused by dropped objects are studied. For this, the impact on an internally pressurized pipeline resting on a flexible bed has been numerically simulated. A relatively extensive parametric study has then been carried out to examine effects from variations in the cement coating thickness, internal pressure, indenter shape, impact velocity and subsoil mechanical properties on the pipeline response. It has been noticed that the presence of internal pressure results in substantial decrease in the impact dent depth, causing the deformation to become spatially more localized. It has also been shown that the flexibility of pipe bed plays an important role in the impact energy dissipation.

scholarly journals Integrating the Shape Constants of a Novel Material Stress-Strain Characterization Model for Parametric Numerical Analysis of the Deformational Capacity of High-Strength X80-Grade Steel Pipelines

2019 ◽  
Vol 9 (2) ◽  
pp. 322 ◽  
Author(s):  
Onyekachi Ndubuaku ◽  
Michael Martens ◽  
J. Cheng ◽  
Samer Adeeb
Keyword(s):  
Axial Compression ◽  
Goodness Of Fit ◽  
Predictive Accuracy ◽  
Limit State ◽  
Pipe Material ◽  
Stress Strain ◽  
Line Pipe ◽  
Diverse Range ◽  
Strain Characterization ◽  
Characterization Model

Pipelines typically exhibit significant inelastic deformation under various loading conditions, making it imperative for limit state design to include considerations for the deformational capacity of pipelines. The methods employed to achieve higher strength of API X80 line pipe steels during the plate manufacturing process tend to increase the hardness of the pipe material, albeit at the cost of ductility and strain hardenability. This study features a simple and robust material stress-strain characterization model, which is able to mathematically characterize the shape of a diverse range of stress-strain curves, even for materials with a distinct yield point and an extended yield plateau. Extensive parametric finite element analysis is performed to study the relationship between relevant parameters and the deformational capacity of API X80 pipelines subjected to uniform axial compression, uniform bending, and combined axial compression and bending. Nonlinear regression analysis is employed to develop six nonlinear semi-empirical equations for the critical limit strain, wherein the shape constants of the material model are adapted as dimensionless parameters. The goodness-of-fit of the developed equations was graphically and statistically evaluated, and excellent predictive accuracy was obtained for all six developed equations.

scholarly journals Damage Evolution of Granodiorite after Heating and Cooling Treatments

Minerals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 779
Author(s):  
Mohamed Gomah ◽  
Guichen Li ◽  
Salah Bader ◽  
Mohamed Elkarmoty ◽  
Mohamed Ismael
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Failure Mode ◽  
Physical And Mechanical Properties ◽  
P Wave ◽  
Physical Parameters ◽  
Slow Cooling ◽  
Heating And Cooling ◽  
Natural Rock ◽  
The Impact

The awareness of the impact of high temperatures on rock properties is essential to the design of deep geotechnical applications. The purpose of this research is to assess the influence of heating and cooling treatments on the physical and mechanical properties of Egyptian granodiorite as a degrading factor. The samples were heated to various temperatures (200, 400, 600, and 800 °C) and then cooled at different rates, either slowly cooled in the oven and air or quickly cooled in water. The porosity, water absorption, P-wave velocity, tensile strength, failure mode, and associated microstructural alterations due to thermal effect have been studied. The study revealed that the granodiorite has a slight drop in tensile strength, up to 400 °C, for slow cooling routes and that most of the physical attributes are comparable to natural rock. Despite this, granodiorite thermal deterioration is substantially higher for quick cooling than for slow cooling. Between 400:600 °C is ‘the transitional stage’, where the physical and mechanical characteristics degraded exponentially for all cooling pathways. Independent of the cooling method, the granodiorite showed a ductile failure mode associated with reduced peak tensile strengths. Additionally, the microstructure altered from predominantly intergranular cracking to more trans-granular cracking at 600 °C. The integrity of the granodiorite structure was compromised at 800 °C, the physical parameters deteriorated, and the rock tensile strength was negligible. In this research, the temperatures of 400, 600, and 800 °C were remarked to be typical of three divergent phases of granodiorite mechanical and physical properties evolution. Furthermore, 400 °C could be considered as the threshold limit for Egyptian granodiorite physical and mechanical properties for typical thermal underground applications.

An estimate of the stress-strain and limiting states of composite tanks under internal pressure

1981 ◽  
Vol 17 (2) ◽  
pp. 180-183
Author(s):  
G. P. Zaitsev ◽  
V. M. Vasilevskii ◽  
A. V. Gollandtsev ◽  
N. I. Kopyl
Keyword(s):  
Internal Pressure ◽  
Stress Strain

Stress-strain curve of paper revisited

2012 ◽  
Vol 27 (2) ◽  
pp. 318-328 ◽  
Author(s):  
Svetlana Borodulina ◽  
Artem Kulachenko ◽  
Mikael Nygårds ◽  
Sylvain Galland
Keyword(s):  
Three Dimensional ◽  
Strain Curve ◽  
Failure Behavior ◽  
Three Dimensional Model ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Fiber Network ◽  
Bonding Parameters ◽  
Particle Level ◽  
The Impact

Abstract We have investigated a relation between micromechanical processes and the stress-strain curve of a dry fiber network during tensile loading. By using a detailed particle-level simulation tool we investigate, among other things, the impact of “non-traditional” bonding parameters, such as compliance of bonding regions, work of separation and the actual number of effective bonds. This is probably the first three-dimensional model which is capable of simulating the fracture process of paper accounting for nonlinearities at the fiber level and bond failures. The failure behavior of the network considered in the study could be changed significantly by relatively small changes in bond strength, as compared to the scatter in bonding data found in the literature. We have identified that compliance of the bonding regions has a significant impact on network strength. By comparing networks with weak and strong bonds, we concluded that large local strains are the precursors of bond failures and not the other way around.

On Thick-Walled Cylinder Under Internal Pressure

2003 ◽  
Vol 125 (3) ◽  
pp. 267-273 ◽  
Author(s):  
W. Zhao ◽  
R. Seshadri ◽  
R. N. Dubey
Keyword(s):  
Internal Pressure ◽  
Strain Curve ◽  
Stress Strain ◽  
Piecewise Linearization ◽  
Elastic Plastic ◽  
Plastic Cylinder ◽  
Parametric Functions ◽  
The Difference ◽  
New Formulation ◽  
Walled Cylinder

A technique for elastic-plastic analysis of a thick-walled elastic-plastic cylinder under internal pressure is proposed. It involves two parametric functions and piecewise linearization of the stress-strain curve. A deformation type of relationship is combined with Hooke’s law in such a way that stress-strain law has the same form in all linear segments, but each segment involves different material parameters. Elastic values are used to describe elastic part of deformation during loading and also during unloading. The technique involves the use of deformed geometry to satisfy the boundary and other relevant conditions. The value of strain energy required for deformation is found to depend on whether initial or final geometry is used to satisfy the boundary conditions. In the case of low work-hardening solid, the difference is significant and cannot be ignored. As well, it is shown that the new formulation is appropriate for elastic-plastic fracture calculations.

Ratcheting assessment of corroded elbow pipes subjected to internal pressure and cyclic bending moment

2021 ◽  
pp. 030932472198989
Author(s):  
Ali Salehi ◽  
Armin Rahmatfam ◽  
Mohammad Zehsaz
Keyword(s):  
Growth Rate ◽  
Stainless Steel ◽  
Internal Pressure ◽  
Bending Moment ◽  
Axial Direction ◽  
Hoop Strain ◽  
Cyclic Bending ◽  
High Fatigue ◽  
The Impact ◽  
Cyclic Bending Moment

The present study aimed to study ratcheting strains of corroded stainless steel 304LN elbow pipes subjected to internal pressure and cyclic bending moment. To this aim, spherical and cubical shapes corrosion are applied at two depths of 1 mm and 2 mm in the critical points of elbow pipe such as symmetry sites at intrados, extrados, and crown positions. Then, a Duplex 2205 stainless steel elbow pipe is considered as an alternative to studying the impact of the pipe materials, due to its high corrosion resistance and strength, toughness, and most importantly, the high fatigue strength and other mechanical properties than stainless steel 304LN. In order to perform numerical analyzes, the hardening coefficients of the materials were calculated. The results highlight a significant relationship between the destructive effects of corrosion and the depth and shape of corrosion, so that as corrosion increases, the resulting destructive effects increases as well, also, the ratcheting strains in cubic corrosions have a higher growth rate than spherical corrosions. In addition, the growth rate of the ratcheting strains in the hoop direction is much higher across the studied sample than the axial direction. The highest growth rate of hoop strain was observed at crown and the highest growth rate of axial strains occurred at intrados position. Altogether, Duplex 2205 material has a better performance than SS 304LN.

Strength of a Pipe Mitred Bend

1970 ◽  
Vol 92 (4) ◽  
pp. 767-773 ◽  
Author(s):  
Jaroslaw Sobieszczanski
Keyword(s):  
Internal Pressure ◽  
Maximum Stress ◽  
Cylindrical Shells ◽  
Beam Theory ◽  
The Self ◽  
Design Work ◽  
Stress And Deformation

Single and multiple mitred bends are analyzed for stress and deformation due to inplane bending and internal pressure. Theory of cylindrical shells is used as a tool of analysis. Results show maximum stress at the elbow increased up to more than 400 percent of the stress predicted by elementary beam theory. Influence of the elbow on the self-compensation of the heated pipeline is discussed and the local reinforcements proposed. Solutions are presented as graphs which may be directly applied in design work.

Impact of random soil properties on stress–strain response

2004 ◽  
Vol 41 (2) ◽  
pp. 351-355 ◽  
Author(s):  
Dieter Stolle ◽  
Peijun Guo ◽  
Gabriel Sedran
Keyword(s):  
Soil Properties ◽  
Constitutive Modelling ◽  
Soil Parameters ◽  
Strain Response ◽  
Constitutive Behaviour ◽  
Stress Strain ◽  
Deterministic Analysis ◽  
Model Predictions ◽  
Random Variability ◽  
The Impact

This paper analyzes the impact of natural random variation of soil properties on the constitutive modelling of geomaterial behaviour. A theoretical framework for accommodating variation in soil properties is presented. The framework is then used to examine the consequence of parameter variability on stress–strain relations. An important observation is that average soil parameters from a series of tests on small specimens, in which density of the specimens varies randomly, do not necessarily reflect the average constitutive behaviour of soil. Model predictions are shown to be consistent with the experimental data.Key words: random variability, deterministic analysis, soil parameters, constitutive model.

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