Pipe Elements Research Articles

Potential risk of vapour cloud explosion in FLNG liquefaction modules

Floating Production Storage and Offloading vessels have been in operation for four decades and there are now well over 250 vessels in existence, but their gas equivalent floating liquid natural gas plants kwon as FLNGs are still very new. Consequently designs and arrangement of top-side process units are still evolving and their safety has yet to be fully and objectively evaluated. This paper explores the probability of occurrence of accidents leading to vapour cloud explosion at one of the topside liquefaction modules of an FLNG. The worst possible scenario with the maximum tolerable probability is identified and the impact of the corresponding vapour cloud explosion is estimated. The strength of the structures supporting the neighbouring modules was examined using finite element analysis to determine if the accident has a potential of escalating to neighbouring modules.It is found that the current levels of safety gaps between the liquefaction modules may be insufficient for the structural arrangement in place. It is thought that a new structural design using circular pipes as the structural elements instead of the I-beams may enhance the integrity of the top-side supporting structures against the impact of potential vapour cloud explosion. The effectiveness of the new structure is demonstrated by comparing it to the conventional supporting structure using I-beam members. This also implies that, by using pipe elements, the safety gaps can be reduced, thus making it possible to optimise the topside arrangement more easily.

Measurement of Residual Creep Deformation of Elements of High-Temperature, High-Chromium Steel Steam Pipes Without Using Reference Marks

The urgency of testing residual creep deformation of high-chromium steel steam pipes is substantiated. For cases when the high-chromium steel pipes are delivered from the manufacturer without reference marks, it is suggested to measure residual creep deformation not by the traditional method, i.e., without the use of reference marks. For this purpose, the design of a device enabling checking residual deformation directly on the outside surface of a pipe element is proposed and the principle of action of this device is described. The acceptable accuracy and reproducibility of the measurement results by means of the proposed device is substantiated.

Dynamic analysis of the reciprocating compressor package on the offshore platform

Reciprocating compressor packages are key equipment for the offshore platforms which are used for the pressurization and transportation of natural gas. Dynamic analyses of high-speed and flexible supported offshore compressor packages are more complex than that of compressors on land. The dynamic analysis techniques of the offshore reciprocating compressor package were studied including numerical modelling, excitation forces calculation, support boundary determination of the compressor package and load transmission between the compressor package and the offshore platform. The finite element model of the compressor package with multiple types of elements such as the pipe, beam and shell elements were established. Excitation forces mainly including gas forces inside cylinders, crosshead forces, acoustic shaking forces and unbalanced inertia forces were calculated. In order to investigate the influence of the flexibility of the platform on dynamic characteristics of the compressor package and set reasonable boundaries for the support structure, three kinds of support boundaries were compared. The support points of columns and vertical beams on the layer of deck where the compressor package is installed were determined to be the most suitable ones. Super-element method was applied to implement the load transmission from the compressor package to the platform. The analysis techniques herein were successfully applied to the dynamic analysis of an offshore reciprocating compressor package in an engineering project.

Sand erosion measurements under multiphase annular flow conditions in a horizontal-horizontal elbow

Gas-liquid annular flow is commonly observed in natural gas transmission and offshore horizontal pipelines. The presence of sand particles in such flows can cause severe equipment degradation of piping elements. The most vulnerable parts of pipeline systems tend to be components in which the flow direction changes suddenly such as elbows and tees. This paper presents the results of an experimental study on erosion in an elbow under gas-liquid-sand flow conditions. Firstly, erosion patterns and mass loss measurements were obtained in a test cell with paint erosion approach and aluminum elbow specimen. Secondly, a non-invasive Ultrasonic Technology (UT) device was employed to achieve erosion patterns in a 76.2mm ID stainless steel standard elbow. The wall-thickness loss was measured at 16 different locations on the elbow using dual element ultrasonic transducers. Experiments were performed with superficial gas velocities ranging from 27m/s to 49m/s at nearly atmospheric pressure. Superficial liquid velocities varied from 0.005m/s to 0.457m/s. In all cases examined, the orientation of the elbow was horizontal-horizontal. Three different sand sizes (20, 150 and 300μm sand) were used for performing the tests. Experimental results showed different erosion behaviors with variations of flow patterns in the horizontal-horizontal elbow (H-H). The data were also compared to some erosion data previously obtained in a vertical-horizontal elbow that shows erosion in H-H elbow is much smaller than V-H elbows for some of the multiphase flow conditions. In summary, the effects of different parameters such as sand size and liquid viscosity on measured erosion rates were investigated.

Dynamic simulation of gas pipeline networks with electrical analogy

Modeling and simulation of natural gas transmission and distribution networks aims to identify and predict the behavior of gas flow so as to perform better monitoring and managing of gas networks. To predict the rate and pressure of gas flow the classical models still use the partial differential equations. In this study, a relatively new approach based on an electrical analogy has been presented which leads to an algebraic and a first-order ordinary differential equation. The solution to these equations is simpler and faster relative to the partial equations. In the proposed model, the effect of pipeline inclination has been considered. To improve the level of predicting mass storage inside the pipe elements, a correction factor in the capacitor equation is also used. The model validation is carried out by comparing the results with some available experimental data and published numerical simulation results, which shows a very good agreement.

On the formulation of a multi-layered composite pipe finite element with an arbitrary variable wall thickness-Part 1: Static postbuckling analysis with unstable large deformation

A multi-layered composite pipe finite element is developed, in which the wall thickness and the reference surface of each layer can be arbitrary functions of circumferential and axial directions. The kinematics of this multi-layered composite pipe element is set up. Explicit formulations for the Jacobian matrix and its determinant are obtained. The high-order modal displacement test/trial function are applied. To satisfy the compatibility condition between adjacent layers, the interface traction DOF (degree of freedom) is induced and the mixed formulation is obtained. The Dirac's Delta function defined on the interfaces is used as the interpolation function of the traction field. The static condensation technique is applied so that the DOFs of traction are eliminated on the element level. The implementation details of the nonlinear finite element for the multi-layered composite pipe element are also presented. Large deformation and finite strain are both considered. The UL (Updated Lagrangian) form is applied. This multi-layered composite pipe element is applied to solve the multi-layered pipe buckling problem. The results are compared with those from ANSYS.

A New Holistic Approach for Subsea Pipeline Upheaval Buckling Design

For a trenched and buried pipeline, the propensity to upheaval buckling (UHB) is a major design concern. Predictive UHB design is typically required at the outset to determine both trenching and backfilling requirements. Additional rockdump schedule can be established by analyzing post pipelay out of straightness (OOS) survey data incorporating appropriate safety factors based on a structural reliability analysis (SRA). The normal approach is to examine the as-laid pipeline imperfection survey statistics and data accuracy. The structural reliability analysis and load factor calculation are typically performed a priori based on the assumed initial imperfections using the universal design curve methodology. A new pseudo-energy method for UHB and OOS is proposed and discussed in this paper based on the variational principle and modal analysis. The approach takes into account the effects of varying effective axial force, trench imperfections, and vertical uplift resistance, by combining both axial friction and lateral resistance methods into a unified model. A new concept, effective uplift resistance and associated load, is also introduced to deal with nonuniform backfill cover. Adjacent imperfections and backfill profiles are considered in detail. A finite element (FE) model is developed to consist of three-noded quadratic pipe elements using abaqus Ver 6.12, and iterations of FE analyses are performed to demonstrate the tangible benefits of the approach specifically for UHB OOS design in relation to target trenching and backfilling, leading to improved reliability and potential cost saving in UHB OOS design and rockdump installation.

The Effect of P-Wave Propagation on the Seismic Behavior of Steel Pipelines

Underground structures perceived as one the most vital infrastructures,which include a variety of tunnels, subway lines,gas, oil and water pipe. Plenty of studies devoted to the investigationof the effect of wave propagation method on the seismicbehavior of steel pipelines. It should be mentioned thatanalyses have been carried out on both clayey and sandy soilwith different propagation speed in each of them. The aim ofthis research is the investigation of the effect of longitudinalp-wave propagation method on the amount of nonlinear strainsof pipeline with different way such as Pipe and Psi element or2D modelling of soil. It became evident that the amounts ofMaximum tension strain produced in the pipe have the maximumdifference, equaling 3.4 per cent. In addition, it investigatesthe effect of frequency of input motion on nonlinearstrains and the effect of frequency content in the results.

Express-evaluation of conditions of operated drill pipe elements failure in tripping

Express-evaluation of conditions of operated drill pipe elements failure in tripping

An Approximate Method for Stress Analysis in Butt Joints of FRP Pipelines

Butt joint is a standard connection type for FRP pipelines. Shear stresses are taking place on the interfaces between the wrapping layer and the pipeline. An analytical model for calculating above stresses for joints subjected to axial loading is presented. The model is based on the equilibrium equations of an adhesive element and the bonded pipe elements, as well as the material properties of the anisotropic pipe wall, the wrapping element and the adhesive. Numerical results for typical FRP joints are derived and commented.

連続配管要素体系における流れ加速型腐食による減肉傾向

連続配管要素体系における流れ加速型腐食による減肉傾向

Research into defectiveness of welded joints of steam pipes operated over a long time

The welded joints of steam pipelines of the power units of thermal power plants, which are operated for long periods under conditions of creep and low-cycle fatigue, are the most damaged elements of power units. By the attributes of cohesion, we presented the classification of the types in the defectiveness of the welded joints of steam pipelines, which is appropriate to use for refining the special features of physical-chemical processes and structural changes that occur in metal of the welded joints of steam pipelines. The represented types of damages are characteristic for the welded joints, which exhausted their base resource, including the prolonged one. We revealed the most characteristic places of defectiveness in metal of the welded joints and orienting of cracks towards the weld metal, as well as the metallographic attribute of defectiveness. The physical-chemical processes are examined, which specify structural changes in the long-operated welded joints of steam pipelines. We examined the process of slowing down the dislocations by the carbide precipitates, which coagulate lengthwise and, in the form of intermittent chains, are concentrated along the boundaries of grains of the α-phase. We established that the creep pores to the largest degree are formed in the places of contact between coagulating carbides and grains of the α-phase. It was revealed that the creep cracks are formed at the sections of incomplete recrystallization of the heat-affected zone of welded joints (about 75 %), the fusion (approximately 15 %), while the rest is at other sections of HAZ, as well as in the weld metal and in the base metal. It is demonstrated that the creep cracks developed by the brittle mechanism, which is contributed by the presence of segregations in the near-boundary zones of grains of the α-phase. We established that the fatigue cracks predominantly develop at the section of fusion, overheating and incomplete recrystallization of HAZ, as well as near the backing rings in the places of contact of the pipe elements with different thickness. Dependence is detected of the reduction in metal resistance of the long operated welded joints of steam pipelines to the formation of fatigue cracks on the level of degradation of their structure. Data of present study are necessary for obtaining welded joints with decreased defectiveness in the process of prolonged operation under conditions of creep and low-cycle fatigue.

Pressure drop of two-phase helium along long cryogenic flexible transfer lines to support a superconducting RF operation at its cryogenic test stand.

BackgroundEstablishing a stand-alone cryogenic test stand is of vital importance to ensure the highly reliable and available operation of superconducting radio-frequency module in a synchrotron light source. Operating a cryogenic test stand relies strongly on a capability to deliver two-phase helium along long cryogenic transfer lines. A newly constructed cryogenic test stand with flexible cryogenic transfer lines of length 220 m at National Synchrotron Radiation Research Center is required to support a superconducting radio-frequency module operated at 126.0 kPa with a 40-W dynamic load for a long-term reliability test over weeks. It is designed based on a simple analytical approach with the introduction of a so-called tolerance factor that serves to estimate the pressure drops in transferring a two-phase helium flow with a substantial transfer cryogenic heat load. Tolerance factor 1.5 is adopted based on safety factor 1.5 commonly applied in cryogenic designs to estimate the total mass flow rate of liquid helium demanded. A maximum 60-W dynamic load is verified with experiment measured with heater power 60 W instead after the cryogenic test stand has been installed.ResultsAligning the modeled cryogenic accumulated static heat load with the results measured in situ, actual tolerance factor 1.287 is obtained. The feasibility and validity of our simple analytical approach with actual tolerance factor 1.287 have been scrutinized by using five test cases with varied operating conditions. Calculated results show the discrepancies of the pressure drops between the estimated and measured values for both liquid helium and cold gaseous helium transfer lines have an underestimate 0.11 kPa and an overestimate 0.09 kPa, respectively. A discrepancy is foreseen, but remains acceptable for engineering applications from a practical point of view.ConclusionsThe simple analytical approach with the introduction of a tolerance factor can provide not only insight into optimizing the choice of each lossy cryogenic piping element of the transfer lines in the design phase but also firm guidance for upgrading the present cryogenic transfer lines for its subsequent application.

On the formulation of a pipe element II: An orthogonal polynomial pipe element

Based on the previous work of the variable wall thickness pipe element Li (2016), an orthogonal polynomial pipe element is developed in this paper. The orthogonal polynomial theory is applied in the displacement basis functions. By choosing some particular orthogonal polynomials as the basis function, the element mass matrix and total mass matrix are both tri-diagonal matrix, which is meaningful for the explicit dynamical analysis. This paper presents a systematical method of how to design the basis functions. Given the pipe configuration and boundary conditions, a unique basis function can be obtained to generate a tri-diagonal mass matrix accurately. The values of the non-zero terms of the tri-diagonal mass matrix can be pre-calculated.In order to satisfy the displacement circumferential periodical condition and the contact constraint condition, the Lagrangian multiplier method or MPC (multi-points constraint) is applied. The additional force degree is eliminated in the element level so that the tri-diagonal mass matrix is maintained. Since the orthogonal polynomial is applied, a high-order resolution is obtained.To prove the accuracy of this orthogonal polynomial pipe element, the problems of the pipe dynamical buckling propagation are analyzed. The numerical simulation results are compared with experiment results from other papers.

Transversally enriched pipe element method (TEPEM): An effective numerical approach for blood flow modeling.

In this work, we present a novel approach tailored to approximate the Navier-Stokes equations to simulate fluid flow in three-dimensional tubular domains of arbitrary cross-sectional shape. The proposed methodology is aimed at filling the gap between (cheap) one-dimensional and (expensive) three-dimensional models, featuring descriptive capabilities comparable with the full and accurate 3D description of the problem at a low computational cost. In addition, this methodology can easily be tuned or even adapted to address local features demanding more accuracy. The numerical strategy employs finite (pipe-type) elements that take advantage of the pipe structure of the spatial domain under analysis. While low order approximation is used for the longitudinal description of the physical fields, transverse approximation is enriched using high order polynomials. Although our application of interest is computational hemodynamics and its relevance to pathological dynamics like atherosclerosis, the approach is quite general and can be applied in any internal fluid dynamics problem in pipe-like domains. Numerical examples covering academic cases as well as patient-specific coronary arterial geometries demonstrate the potentialities of the developed methodology and its performance when compared against traditional finite element methods. Copyright © 2016 John Wiley & Sons, Ltd.

An accurate and computationally efficient small-scale nonlinear FEA of flexible risers

This paper presents a highly efficient small-scale, detailed finite-element modelling method for flexible risers which can be effectively implemented in a fully-nested (FE2) multiscale analysis based on computational homogenisation. By exploiting cyclic symmetry and applying periodic boundary conditions, only a small fraction of a flexible pipe is used for a detailed nonlinear finite-element analysis at the small scale. In this model, using three-dimensional elements, all layer components are individually modelled and a surface-to-surface frictional contact model is used to simulate their interaction. The approach is applied on a 5-layered pipe made of inner, outer and intermediate polymer layers and two intermediate armour layers, each made of 40 steel tendons. The capability of the method in capturing the detailed nonlinear effects and the great advantage in terms of significant CPU time saving are demonstrated by comparing the results obtained on elements of pipe of different lengths, equal to one pitch length Lp as well as Lp/5, Lp/20 and Lp/40.

Dynamic Characteristics of Fluid-Conveying Pipes with Piecewise Linear Support

For the analysis of dynamic characteristics of fluid-conveying pipes with piecewise linear support, a fluid–structure coupling dynamic model based on the finite element method is proposed. A user-defined pipe element based on Euler–Bernoulli beam is developed for modeling the pipes, considering the dynamic flow conditions. A nonlinear spring element is utilized to model the clamp between the pipe and the base. The dynamic responses of the system are obtained through the direct time integration. The stiffness of the clamp support is investigated by the analytical method and the experimental method, in which it is found that the clamp stiffness is piecewise linear. For different pipe geometries the user-defined element model, analytical model and measurement data are compared. The results show high quality of the element developed in this paper. Finally, the dynamic characteristics of the pipe system with piecewise linear support subjected to base harmonic excitation are calculated and the effects of the system parameters on pipe behaviors have also been studied. As a consequence, the model proposed in this paper can represent the piecewise linear nonlinearity of the clamp support and be used conveniently to investigate the effects of the fluid–structure coupling on the system behaviors.

On the formulation of a pipe element for a pipe structure with variable wall thickness

In this paper, a pipe element is developed for a pipe structure with variable wall thickness. The variable wall thickness field tw can be an arbitrary function about circumferential and axial directions. A local dimensionless cylindrical coordinate system is set up. The displacement expression is defined based on the local dimensionless cylindrical coordinate system. The map from the local dimensionless cylindrical coordinate system to the pipe structure configuration is established. In the circumferential and radial dimensions, the series is used as the displacement basis functions. In the axial direction, Lagrangian interpolation is applied. Furthermore, the referential surface R can also be defined as an arbitrary function about circumferential and axial directions as tw. Thus, this pipe element has wide applications. The complicated problems with geometrical nonlinearity (large deformation and finite strain) can be analyzed well by this element. The pipe buckle crossover problem is analyzed in this paper. In this problem, the pipe model has an axially variable wall thickness field. The eccentric pipe collapse problem is also analyzed. In this problem, the pipe model has a circumferential variable wall thickness field. The results are compared with those from other well-established FEM simulations.

Свойства циклид дюпена и их применение. Часть 4: приложения

In the first and second parts of the work there were
 considered mainly properties of Dupin cyclide, and given some
 examples of their application: three ways of solving the problem of
 Apollonius using only compass and ruler, using the identified properties
 of cyclide; it is determined that the focal surfaces of Dupin
 cyclid are degenerated in the lines and represent curves of the
 second order – herefrom Dupin cyclide can be defined by conic curve and a sphere whose center lies on the focal curve. Polyconic
 compliance of these focal curves is identified. The formation of the
 surface of the fourth order on the basis of defocusing curves of the
 second order is shown.
 In this issue of the journal the reader is invited to consider the
 practical application of Dupin cyclide’s properties. The proposed
 solution of Fermat’s classical task about the touch of the four
 spheres by the fifth with a ruler and compass, i.e., in the classical
 way. This task is the basis for the problem of dense packing. In the
 following there is an application of Dupin cyclide as a transition
 pipe element, providing smooth coupling of pipes of different diameters
 in places of their connections. Then the author provides
 the examples of Dupin cyclide’s application in the architecture as
 a shell coating. It is shown how to produce membranes from the
 same cyclide’s modules, from different modules of the same cyclide,
 from the modules of different cyclides, from cyclides with the inclusion
 of other surfaces, special cases of cyclides in the educational
 process. The practical application of the last problem found the
 place in descriptive geometry at the final geometrical education of
 architects in the "Construction of surfaces". Here such special cased
 of cyclides as conical and cylindrical surfaces of revolution.

Vibration analysis of composite pipes using the finite element method with B-spline wavelets

A finite element formulation using the B-spline wavelets on the interval is developed for modeling the free vibrations of composite pipes. The composite FRP pipe element is treated as a beam element. The finite pipe element is constructed in the wavelet space and then transformed to the physical space. Detailed expressions of the mass and stiffness matrices are derived for the composite pipe using the B-spline scaling and wavelet functions. Both Euler-Bernoulli and Timoshenko beam theories are considered. The generalized eigenvalue problem is formulated and solved to obtain the modal characteristics of the composite pipe. The developed wavelet-based finite element discretization scheme utilizes significantly less elements compared to the conventional finite element method for modeling composite pipes. Numerical solutions are obtained to demonstrate the accuracy of the developed element, which is verified by comparisons with some available results in the literature.