Bending Capacity of Pipe Bends in Deepwater Conditions

2010 ◽  
Author(s):  
Shulong Liu ◽  
Alastair Walker ◽  
Philip Cooper
Keyword(s):  
Internal Pressure ◽  
Induction Heating ◽  
Wall Thickness ◽  
Failure Modes ◽  
Limit State ◽  
Bending Moment ◽  
External Pressure ◽  
Fe Method ◽  
Moment Capacity ◽  
Operation Conditions

Offshore pipeline systems commonly incorporate induction-heating formed bends along flowlines and in pipeline end termination assemblies and spools. In deepwater locations, the pipeline and bends are subjected to various combinations of external pressure, internal pressure, bending moment and temperature changes, during installation, and operation. Although there is a history of research into the limiting loads and failure modes of such bends and pipelines systems there is, as yet, no comprehensive guidance to enable the calculation of the maximum capacity under combined bending and external pressure loading. Conservative guidance is presented in DNV OS-F101 (2007) [1] that proposes increasing the pipe wall thickness to reduce the effect of external pressure collapse effects thus enabling bending formulations relevant to straight pipe to be used. This proposed approach leads to unfeasibly large wall thickness requirements in very deepwater applications. There is therefore a requirement for a method to design deepwater bends for installation and operation conditions with levels of safety comparable with those used in the design of straight sections of pipelines that does not depend on the requirement to increase the wall thickness to the extent proposed in the current DNV guidance. In this study, a nonlinear FE method using ABAQUS is proposed to evaluate the ultimate capacities of induction-heating formed bends. The method takes into account the combined effects of non-linear material properties, initial ovality, wall thinning/thickening, external or internal pressure, internal CRA cladding and temperature change on the ultimate moment capacity of the bend. The numerical model is validated by comparison with available published results. The method developed here is based on the limit state design formulations in the current DNV OS-F101 guidance.

Submarine Pipeline Installation JIP: Strength and Deformation Capacity of Pipes Passing Over the S-Lay Vessel Stinger

2006 ◽  
Author(s):  
Enrico Torselletti ◽  
Luigino Vitali ◽  
Erik Levold ◽  
Kim J. Mo̸rk
Keyword(s):  
Water Depth ◽  
Failure Modes ◽  
Bending Moment ◽  
External Pressure ◽  
Submarine Pipeline ◽  
Design Guideline ◽  
Moment Capacity ◽  
Sea Bottom ◽  
Major Vessel ◽  
Gas Fields

The development of deep water gas fields using trunklines to carry the gas to the markets is sometime limited by the feasibility/economics of the construction phase. In particular there is a market for using S-lay vessels in water depth larger than 1000m. The S-lay feasibility depends on the applicable tension at the tensioner which is a function of water depth, stinger length and stinger curvature (for given stinger length by its curvature). This means that, without major vessel up-grading and to avoid too long stingers that are prone to damages caused by environmental loads, the application of larger stinger curvatures than presently allowed by current regulations/state of the art is needed. The work presented in this paper is a result of the project “Development of a Design Guideline for Submarine Pipeline Installation” sponsored by STATOIL and HYDRO. The technical activities are performed in co-operation by DNV, STATOIL and SNAMPROGETTI. The scope of the project is to produce a LRFD (Load Resistant Factor Design) design guideline to be used in the definition and application of design criteria for the laying phase e.g. to S and J-lay methods/equipment. The guideline covers D/t from 15 to 45 and applied strains over the overbend in excess of 0.5%. This paper addresses the failure modes relevant for combined high curvatures/strains, axial, external pressure and local forces due to roller over the stinger of an S-lay vessel and to sea bottom contacts, particularly: • Residual pipe ovality after laying, • Maximum strain and bending moment capacity. Analytical equations are proposed in accordance with DNV OS F101 philosophy and design format.

Minimum Wall Thickness Requirements for Ultra Deep-Water Pipelines

2003 ◽  
Author(s):  
Enrico Torselletti ◽  
Luigino Vitali ◽  
Roberto Bruschi ◽  
Leif Collberg
Keyword(s):  
Wall Thickness ◽  
Deep Water ◽  
Failure Modes ◽  
Limit State ◽  
Strain Curve ◽  
External Pressure ◽  
Design Guidelines ◽  
Compressive Yield Strength ◽  
Pipe Material ◽  
Line Pipe

The offshore pipeline industry is planning new gas trunklines at water depth ever reached before (up to 3500 m). In such conditions, external hydrostatic pressure becomes the dominating loading condition for the pipeline design. In particular, pipe geometric imperfections as the cross section ovality, combined load effects as axial and bending loads superimposed to the external pressure, material properties as compressive yield strength in the circumferential direction and across the wall thickness etc., significantly interfere in the definition of the demanding, in such projects, minimum wall thickness requirements. This paper discusses the findings of a series of ultra deep-water studies carried out in the framework of Snamprogetti corporate R&D. In particular, the pipe sectional capacity, required to sustain design loads, is analysed in relation to: • The fabrication technology i.e. the effect of cold expansion/compression (UOE/UOC) of TMCP plates on the mechanical and geometrical pipe characteristics; • The line pipe material i.e. the effect of the shape of the actual stress-strain curve and the Y/T ratio on the sectional performance, under combined loads; • The load combination i.e. the effect of the axial force and bending moment on the limit capacity against collapse and ovalisation buckling failure modes, under the considerable external pressure. International design guidelines are analysed in this respect, and experimental findings are compared with the ones from the application of proposed limit state equations and from dedicated FE simulations.

Elastic-plastic bending of the pipeline under combined loading

2021 ◽  
pp. 372-377
Author(s):  
Виктор Миронович Варшицкий ◽  
Евгений Павлович Студёнов ◽  
Олег Александрович Козырев ◽  
Эльдар Намикович Фигаров
Keyword(s):  
Internal Pressure ◽  
Limit State ◽  
Bending Moment ◽  
Axial Direction ◽  
Longitudinal Force ◽  
Combined Loading ◽  
Dimensional Problem ◽  
Elastic Plastic ◽  
Pipeline Section ◽  
Thin Walled Pipe

Рассмотрена задача упругопластического деформирования тонкостенной трубы при комбинированном нагружении изгибающим моментом, осевой силой и внутренним давлением. Решение задачи осуществлено по разработанной методике с помощью математического пакета Matcad численным методом, основанным на деформационной теории пластичности и безмоментной теории оболочек. Для упрощения решения предложено сведение двумерной задачи к одномерной задаче о деформировании балки, материал которой имеет различные диаграммы деформирования при сжатии и растяжении в осевом направлении. Проведено сравнение с результатами численного решения двумерной задачи методом конечных элементов в упругопластической постановке. Результаты расчета по инженерной методике совпадают с точным решением с точностью, необходимой для практического применения. Полученные результаты упругопластического решения для изгибающего момента в сечении трубопровода при комбинированном нагружении позволяют уточнить известное критериальное соотношение прочности сечения трубопровода с кольцевым дефектом в сторону снижения перебраковки. Применение разработанной методики позволяет ранжировать участки трубопровода с непроектным изгибом по степени близости к предельному состоянию при комбинированном нагружении изгибающим моментом, продольным усилием и внутренним давлением. The problem of elastic plastic deformation of a thin-walled pipe under co-binned loading by bending moment, axial force and internal pressure is considered. The problem is solved by the developed method using the Matcad mathematical package by a numerical method based on the deformation theory of plasticity and the momentless theory of shells. To simplify the solution of the problem, it is proposed to reduce a twodimensional problem to a one-dimensional problem about beam deformation, the material of which has different deformation diagrams under compression and tension in the axial direction. Comparison with the results of numerical solution of the two-dimensional problem with the finite element method in the elastic plastic formulation is carried out. The obtained results of the elastic-plastic solution for the bending moment in the pipeline section under combined loading make it possible to clarify criterion ratio of the strength of the pipeline section with an annular defect in the direction of reducing the rejection. Application of the developed approach allows to rank pipeline sections with non-design bending in the steppe close to the limit state under combined loading of the pipeline with bending moment, longitudinal force and internal pressure.

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.

Strength and Deformation Capacity of Corroded Pipes: The Joint Industry Project

2013 ◽  
Author(s):  
Erik Levold ◽  
Andrea Restelli ◽  
Lorenzo Marchionni ◽  
Caterina Molinari ◽  
Luigino Vitali
Keyword(s):  
Failure Modes ◽  
State Of The Art ◽  
Local Buckling ◽  
Bending Moment ◽  
External Pressure ◽  
Fe Model ◽  
Deformation Capacity ◽  
Offshore Pipelines ◽  
Strength And Deformation ◽  
Bending Loading

Considering the future development for offshore pipelines, moving towards difficult operating condition and deep/ultra-deep water applications, there is the need to understand the failure mechanisms and better quantify the strength and deformation capacity of corroded pipelines considering the relevant failure modes (collapse, local buckling under internal and external pressure, fracture / plastic collapse etc.). A Joint Industry Project sponsored by ENI E&P and Statoil has been launched with the objective to quantify and assess the strength and deformation capacity of corroded pipes in presence of internal overpressure and axial/bending loading. In this paper: • The State-of-the-Art on strength and deformation capacity of corroded pipes is presented; • The full-scale laboratory tests on corroded pipes under bending moment dominated load conditions, performed at C-FER facilities, are shown together with the calibrated ABAQUS FE Model; • The results of the ABAQUS FEM parametric study are presented.

DESIGN OF BOLTED CONNECTIONS SUBJECT TO TORSION AND SHEAR IN THE ULTIMATE LIMIT STRESS STATE

2019 ◽  
Vol 6 (1) ◽  
Author(s):  
Mohamed S. Abu-Yosef ◽  
Ezzeldin Y. Sayed-Ahmed ◽  
Emam A. Soliman
Keyword(s):  
Failure Modes ◽  
Focal Point ◽  
Design Method ◽  
Limit State ◽  
Bending Moment ◽  
Steel Structures ◽  
Ultimate Limit State ◽  
Shear Forces ◽  
Limit States ◽  
Ultimate Limit

Steel connections transferring axial and shear forces in addition to bending moment and/or torsional moment are widely used in steel structures. Thus, design of such eccentric connections has become the focal point of any researches. Nonetheless, behavior of eccentric connections subjected to shear forces and torsion in the ultimate limit state is still ambiguous. Most design codes of practice still conservatively use the common elastic analysis for design of the said connections even in the ultimate limit states. Yet, there are some exceptions such as the design method proposed by CAN/CSA-S16-14 which gives tabulated design aid for the ultimate limit state design of these connections based on an empirical equation that is derived for ¾ inch diameter A325 bearing type bolts and A36 steel plates. It was argued that results can also be used with a margin of error for other grade bolts of different sizes and steel of other grades. As such, in this paper, the performance of bolted connection subject to shear and torsion is experimentally investigated. The behavior, failure modes and factors affecting both are scrutinized. Twelve connections subject to shear and torsion with different bolts configurations and diameters are experimentally tested to failure. The accuracy of the currently available design equations proposed is compared to the outcomes of these tests.

Study of Bending Capacity of an HPHT CRA-Lined Seamless Pipeline

2014 ◽  
Author(s):  
Cyprian Gil ◽  
Knut Tørnes ◽  
Per Damsleth
Keyword(s):  
Internal Pressure ◽  
Strain Localization ◽  
Local Buckling ◽  
Bending Moment ◽  
Design Criteria ◽  
Design Codes ◽  
Moment Capacity ◽  
Wide Range ◽  
Global Buckling ◽  
The Moment

A study has been performed to better understand ultimate bending moment and strain capacities of pipelines in relation to criteria defined in the design codes. An 18″ HPHT flowline was designed to undergo global buckling on uneven seabed and to resist trawl gear interference. The high temperature (155 degC) and pressure (300 bar) posed considerable design challenges for material selection and design criteria. A CRA-lined X60 CMn pipeline was selected for the project. The pipeline was of seamless manufacture for which the stress/strain characteristics are subject to the effect of Lüders bands. The DNV-OS-F101 code covers a wide range of D/t but does not specifically address Lüder’s material behaviour which could significantly reduce the bending moment capacity of pipe. The global buckling and trawl pull-over FE analysis results indicated the pipe was highly utilized, requiring excessive amounts of seabed intervention at great cost to meet the DNV LCC criteria. Detailed FE simulation of limit states for local buckling and strain localization of a 3D solid element pipe model was performed, with both Roundhouse and Lüders material properties, to investigate pipe capacity in relation to that stipulated by the design codes. The pipe moment capacity was established by obtaining the moment curvature relationship by bending the local pipe section subject to internal pressure until the maximum resistance was reached. Imperfections were introduced to initiate local buckling at the desired location. To determine strain concentration factors and strain localization, the effects of thickness changes and weld misalignment were also studied. The DNV OS-F101 LCC moment criterion formulation computes a decreasing moment capacity for increasing internal pressure. It has been suggested in the literature that this is correct for higher D/t but the criterion may be conservative for pipes with lower D/t. The combination of Lüders material with low D/t is not specifically addressed by any design code. Clarification of these aspects will provide a better understanding of the risk of failure for highly utilized seamless pipelines and allow for modified design criteria that will reduce seabed intervention costs. The results of the study showed that a higher bending moment criterion and associated strain criterion could be adopted for the design that allows for the higher initial strain caused by Lüder’s plateau. The ultimate bending moment capacity of low D/t pipe with Lüder’s material was found to be similar to that of Roundhouse material due to work hardening. In addition, it was demonstrated that the potential strength of the CRA liner could enhance the moment capacity of the seamless pipe.

Reliability Analysis of Land Pipelines for Hydrocarbons Transportation in Mexico

2004 ◽  
Author(s):  
David De Leon ◽  
Carlos Cortes
Keyword(s):  
Mechanical Properties ◽  
Stress Concentration ◽  
Internal Pressure ◽  
Failure Modes ◽  
Limit State ◽  
Response Analysis ◽  
Initiation Toughness ◽  
Limit States ◽  
Internal Corrosion ◽  
Maximum Stresses

Pipelines are the most economical way to transport hydrocarbons. In Mexico, PEMEX manages more than 60,000 Km of oil and gas land and marine pipelines. Therefore, their structural integrity must be carefully assessed. Pipeline managers require reliable and realistic codes in order to back up their decisions about design, maintenance and operation. In particular, for safety prediction, the failure modes and uncertainties involved in each loading condition need to be incorporated in the analysis in order to specify the pipelines use thresholds that keep them over acceptable safety levels within their operating lifetimes [1, 2]. For these reasons, a structural reliability formulation appears to be the appropriate framework to perform the evaluation. In this paper, the land pipeline reliability is estimated for the internal pressure, bending and tension failure mode conditions. These loading conditions are applied individually and tension and bending in a combined fashion, and random variability on the internal pressure, steel mechanical properties as well as the degradation effect of internal corrosion due to the transported fluid is included. So far, seamless pipeline is considered as used in Mexico. A set of internal pressures and mechanical properties are randomly generated through Monte Carlo simulation and the pipeline response under each simulated condition is obtained by making use of commercial software. The response analysis resorts on the nonlinear finite element method and it involves the calculation of maximum stresses and stress concentration factors under no corroded and corroded conditions. The following limit states are assessed: 1) the margin between maximum stresses due to internal pressure, tension and bending and the material capacity and 2) the margin between stress concentration factor and fracture initiation toughness. The above described limit states are calculated for no corroded condition and, once the critical failure modes are identified, corrosion effect is included on them. The failure probability is estimated from the response statistics for the considered limit state. The Cornell reliability index and the respective safety factor are also estimated. These results may be further extended and used for risk assessments and code calibration for design, inspection and maintenance of pipelines in Mexico.

Combined Loading Tests of Large Diameter Corroded Pipelines

2000 ◽  
Author(s):  
Marina Q. Smith ◽  
Christopher J. Waldhart
Keyword(s):  
Internal Pressure ◽  
Thermal Stresses ◽  
Failure Modes ◽  
Prediction Models ◽  
Large Diameter ◽  
Bending Moment ◽  
Combined Loading ◽  
Analytical Models ◽  
Bending Load ◽  
Full Scale Tests

Current methods for estimating the remaining strength of aging, corroded pipelines have been restricted to the capabilities of pressure based engineering models that rely on the definition of hoop stress in the pipe wall. Because in practice, pipelines are subjected to a variety of loading conditions (e.g.; axial bending from settlement and thermal stresses) that act in concert with those derived by internal pressure, a multi-year combined testing and analysis program was initiated by the Alyeska Pipeline Service Company aimed at developing computer tools for the prediction of rupture and wrinkling in corroded pipes. During the program, seventeen full-scale tests of mechanically corroded 48-inch diameter (1219-mm), X65 pipes subjected to internal pressure, axial bending, and axial compression were performed to provide data necessary for the verification of analytical models and failure prediction models. While all of the tests were designed to produce rupture, wrinkling, as defined by the occurrence of a limit moment during the application of bending loads, was produced in eleven of the tests either prior to or instead of rupture. Loading of the pipe was intended to simulate that which would be observed by a pipe in-service and included both load control and displacement control of the applied bending load, and in some tests, intended to define the amount of additional pressure required to cause burst after wrinkling was produced. Results of the tests showed that two different failure modes are produced depending on whether the bending moment is transmitted to the pipe as a fixed load or a fixed displacement, and consequently, the burst capacity of the corroded pipe may not be compromised by the presence of axial loads. This paper discusses the tests performed, including a description of the load schedule and corrosion geometries, and key results of the tests that were used in the development of a new strain-based burst prediction procedure for corroded pipes subjected to combined loads.

Stress Analysis of Stainless Steel Elbow and Tee Fittings Subjected to Internal Pressure and External Loads

1999 ◽  
Author(s):  
Toshiyuki Sawa ◽  
Tetsuya Furuya ◽  
Tadahiro Murakami ◽  
Yasuyuki Kagaya
Keyword(s):  
Internal Pressure ◽  
Wall Thickness ◽  
Bending Moment ◽  
Maximum Pressure ◽  
Screw Thread ◽  
The Finite Element Method ◽  
Internal Working ◽  
Stress States ◽  
Screw Threads ◽  
External Loads

Abstract In this paper, mechanical behaviors of the Elbow and Tee fittings connected to pipes by screw threads under internal pressure, external tensile loads and bending moment are analyzed using the Finite Element Method (FEM). FEM code employed is MARC. The maximum Mises stress of the Elbow and Tee fittings are obtained when the wall thickness is changed while the internal working maximum pressure is held constant at 20bar. The elasto-plastic stress states of screw threads the fittings and the pipes are obtained under internal pressure and external loads. Under the assumptions that nodal points are released when the strain of the elements reaches the rupture strain of the fitting’s material, the load when the rupture occurs at the screw thread is analyzed. The safety factor for the wall thickness of the Elbow and Tee fittings used in the experiment is found to be about 5. The results indicate deduced that the dimensions of Elbow and Tee fittings can be reduced. The strength of the fittings under internal pressure and external loads is obtained. It is found that the stress concentrates at the first root of male thread and expected that a fracture initiates at the first root. The strain of the Elbow and Tee fittings subjected to internal pressure were measured by using strain gauges. The numerical results are in a fairly good agreement with the experimental results.

Sign in / Sign up

Export Citation Format

Share Document