Thin-walled Pipes Research Articles

Experimental determination of local head loss of non-coaxial emitters in thin-wall lay-flat polyethylene pipes

The hydraulic performance of thin-wall lay-flat polyethylene pipes with non-coaxial emitters were evaluated in this study. Two experiments were performed to measure the dimensional variation of commercially available lay-flat drip irrigation pipes. A model for estimating the corresponding local head loss was developed and validated using dimensional analysis. The model was then implemented in a finite element algorithm to analyse the hydraulic performance of this type of pipes. Finally, a design example was provided. The results revealed that, for a wall thickness of 0.13 and 0.20 mm, the pipe height and width tended to be equal above a relatively low pressure, and the pipe cross-section rapidly inflated from a quasi-rectangular form to circular. For thicker walls, the equivalent diameter (four times the hydraulic radius) increased continuously with increasing pressure head but it hardly reached its nominal diameter (16 mm). The proposed model indicated that the local head loss was affected by the equivalent diameter, emitter geometry, and flow velocity. The model had high accuracy in determining the local head loss. The estimated results were in close agreement with the measured data. According to the numerical simulation, the ratio of local head loss to total loss along a pipe was up to 74.71%. The design results, when using an earlier model, demonstrated a longer maximum lateral length, since the model did not consider further contraction of the flow caused by pipe deformation. However, the model proposed here could be used in the design of systems for thin-wall lay-flat polyethylene pipes.

Study on Mode Repulsion of Ultrasonic-Guided Waves in Pipe Bends

Abstract The wave motion of guided waves in pipe bends is still veiled in some mystery, which hinders the application of guided-wave techniques in the inspection of pipelines with bends. Mode repulsion, which exists in the wavenumber versus frequency dispersion curves of guided waves in pipe bends, is an intriguing phenomenon deserving in depth study. The governing equation of wave motion in pipe bends, deduced by the semi-analytical finite element (SAFE) method, can be regarded as an eigenvalue problem. The eigenvalue derivatives, with respect to the wavenumber, are investigated to determine whether mode repulsion will occur or not. A term in the second derivative of the eigenvalue is identified to determine the mode repulsions. With respect to symmetry, it is found that mode repulsion only occurs between modes of one and the same type, such as symmetric or antisymmetric modes, and does not occur between modes of different type, like between symmetric and antisymmetric modes. A specific case of mode repulsion in a small-bore thin-walled pipe in the low-frequency range, where relatively fewer modes exist, is further studied, and the interactions between these modes are clarified. The evolutions of mode shapes before and after mode repulsion are further illustrated.

Life Prediction of Thin Wall Pipe for External Superficial Cracked Exposed to Interior Pressure

Life Prediction of Thin Wall Pipe for External Superficial Cracked Exposed to Interior Pressure

Head Loss in Thin-Walled Drip Tapes with Continuous Labyrinth.

Thin-walled drip tapes with continuous labyrinth have been used for irrigation of vegetables and other short-cycle crops, especially due to their low cost. The continuous labyrinths welded into the pipe inner wall affect the head loss along such emitting pipes. In addition, the flow cross section of thin-walled pipes may change due to the effects of the operating pressure, which also has consequences for the head loss. The objective of this work was to investigate experimentally the friction factor and the head loss on thin-walled drip tapes with continuous labyrinths operated under various pressures. Two models of commercial thin-walled drip tapes with continuous labyrinths were evaluated. Nonperforated samples were used to determine the head-loss equations. The equations were adjusted as a function of flow rate and pressure head at the pipe inlet. Alternatively, the diameter in the Darcy–Weisbach equation was adjusted as a function of the pressure head by a power-law model. The possibility of using a mean diameter in the Darcy–Weisbach equation was also analyzed. Experimental investigation indicated that the friction factor in the Darcy–Weisbach equation can be accurately described using a power-law model, like the Blasius equation, but characterized by a coefficient a=0.3442 for the Turbo Tape and a=0.3225 for the Silver Tape. The obtained values of a are larger than those generally used and available in the literature. The influence of the operating pressure on the pipe diameter can be neglected for the purpose of calculating the head loss. The two approaches, considering the variation of the diameter with the pressure head and considering an optimum average diameter for the calculation of head loss by the Darcy–Weisbach equation, produce similar results, allowing accurate prediction of head loss. Evaluating the proposed mathematical models, 95% of predictions presented relative errors of head loss smaller than 5%. For the Turbo Tape, the optimum diameter for the purpose of calculating the head loss is 16.01 mm, which is very close to the value indicated by its manufacturer (15.9 mm). For the Silver Drip, the optimum diameter is 15.71 mm, while the manufacturer gives a value of 16.22 mm, which produces considerable error in the calculation of head loss.

Geometric rigidity of torsion of thin-walled pipes: theory and experiment

Thin-walled rods as structural elements of buildings, structures and machines that absorb torsion deformations are widely used in construction and engineering. Development of analytical methods for solving the problem of torsion of rods of non-circular cross section is one of the most important modern problems of construction mechanics. When solving torsion problems, the geometric rigidity of the section Ik is primarily determined. The analysis of the considered literature sources showed that the study of the problem in question using the isoperimetric properties of cross-sections of rods is very effective. In the present paper, for thin-walled pipes with an arbitrary convex contour and constant wall thickness, the authors obtain calculation formulae that associate the reduced geometric rigidity of the cross-sections of the pipes Ik with their form factor. It allows formulating the isoperimetric properties of the parameter under study depending on the shape of the pipe sections, and using geometric methods to determine the geometric rigidity of the cross-sections of pipes of arbitrary shape and a convex contour. The article also contains the results of experimental studies of triangular pipes confirming this isoperimetric relationship of the reduced geometric rigidity of pipes with the form factor.

Experimental studies of rotatory rolling of long thin-wall pipes

The article considers the application of rotatory rolling of the external surface of a long thin-wall pipe. The author studied the possibility of correcting the form of a thin-wall pipe outer diameter by means of rotatory rolling with cylindrical rollers having a rectilinear generator and set for a self-tightening angle with a simultaneous decrease of the processed surface roughness. Further, the author provide a photo of the measuring device used to define the circular deviation of a thin-wall pipe surface. A polar diagram of the pipe surface as-delivered and its profile record were made. The article provides a photo showing the adjustment process of a rotatory reeling machine with three deformation rollers for treating long thin-wall pipes in the system of a general purpose lathe. The experiment results are presented in the form of a polar diagram and the treated surface profile record. It is shown that after rotatory rolling the circular deviation decrease to 0,1 mm while the surface roughness decreased from Ra 1,83 um to Ra 0,23 um.

Errors in Clamping Thin-Walled Pipe

The errors arising when thin-walled pipe is clamped in a three-jaw chuck are determined. The wraparound jaws are bored so that their internal diameter is consistent with the rated workpiece size. The workpiece is centered with minimal force. The position of the internal surface is measured with respect to 16 points, and then the clamping force is increased to the working value and the measurements are repeated. It is found that, under the action of the clamping force, the workpiece diameter is decreased by a factor of about 0.0004, while the center of the cross section is additionally shifted by about 0.0003 diameter.

Induction heating simulation of the waveguide assembly elements

The waveguide path systems consisting mainly of aluminum alloys with improved weight, size, and electrical parameters are used to ensure the functioning of the spacecraft and its onboard equipment in accordance with a given program. When assembling the elements of the waveguide paths, in particular a thin-walled pipe of rectangular cross section, coupling and flange, induction brazing is used. Element-by-element assembly of lightweight waveguide paths using the method of induction soldering is connected with a number of technological difficulties such as the uneven distribution of temperature fields, the thickness variation of the soldered products and the design features of the inductors. This paper presents a model describing the process of heating a pipe-inductor system during induction brazing. The presented model describes the process of induction heating of the pipe as a separate structural element of the waveguide path. In the process of simulation in the Comsol software, on the basis of numerical simulation methods with the connection of the necessary media involved in induction heating, the pipe heating graphs are obtained.

Experimental fire testing of an innovative three-layer chimney for residential buildings

Fires in residential buildings originating in flue ducts pose a significant problem in Europe, especially in countries where heating systems rely on devices fired with solid fuel. The high temperature of fumes emitted from heating devices is a main cause of fires. In the case of soot fires, the risk increases, as the temperature in the flue duct can exceed 1000 °C. Chimneys are often located close to flammable (wooden) construction materials, which further increase the risk of fire. This article presents statistical data confirming the significance of the problem. The subject of this study is fire safety of a three-layer chimney system. The diameter of the flue duct of the inspected chimney was 180 mm, while air space and insulation measured 30 mm. The main research involved the use of thermocouples and a thermal imaging camera. The analysed chimney is an innovative construction, as it is equipped with an additional insulating air layer. The purpose of the research is to assess the impact of this air layer on fire safety during the use of a three-layer thin-walled flue pipe. The air space discharges heat from the flue duct through a parallel flow of cold air. Analysis explored the impact of the chimney's thermal radiation on unprotected and easily flammable construction materials. Particular attention has been devoted to the impact the air layer has on reduction of the amount of thermal radiation. Final conclusions from the study can be used to increase fire safety of residential buildings. This may be achieved by reducing temperatures emitted from the chimney cladding.

Experimental Study on Residual Cross-Sectional Flattening of Thin-Walled Pipes Under Pure Plastic Bending

Abstract Cross-sectional ovalization (ovalization) usually occurs when thin-walled pipe is subjected to large plastic bending. This paper is concerned with residual deformation of thin-walled pipe's cross section in a radial direction when external bending moment is removed. In order to clarify the fundamental ovalization characteristics, find out what factors influence the residual flattening (value of ovalization), the ovalization behavior is investigated experimentally. The experiments are carried out on 21 stainless steel specimens with different geometric parameters under different bending radii by means of a four-point pure bending device. The residual cross-sectional flattenings are monitored continuously by scanning the cross section periodically along the circumferential direction. From the experimental results, it is observed that the cross-sectional shape of the thin-walled pipe is not perfect standard ellipse, and the appearance of the maximum residual flattening is usually found in the direction normal to the neutral surface. It is also revealed the relationships between the residual flattening and the bending radius, the wall thickness, and the pipe outer diameter, i.e., the residual flattening increases as the bending radius and the wall thickness reduce, but it increases as the outer diameter increases. These results are expected to find their potential application in thin-walled pipe bending operation.

Erratum to: “Numerical investigation of the transferability of ductile fracture behavior between thin-walled surface-cracked pipe, curved wide plate (CWP) and single edge notched tension (SENT) specimens”

Curved wide plate (CWP) and single edge notched tension (SENT) tests are commonly considered for determining the fracture toughnesses of high-strength line-pipe steel for the strain-based design. However, the tearing resistance relationship between these tests and actual thin-walled surface-cracked pipe has not been clearly established. The purpose of this study is to compare the crack growth characteristics of actual pipe, CWP and SENT using the local damage method, which is based on the Gurson-Tvergaard-Needleman (GTN) model. Small-scale testing of smooth round bar tensile and SENT specimens provides the information required to calibrate the damage parameters of the GTN model. Crack growth simulations are then conducted using the calibrated GTN model to evaluate the tearing resistance behaviors of various geometries. The tearing resistances of the CWP and the actual pipe are similar, whereas the SENT specimen exhibits a higher stress triaxiality. However, this tendency of SENT specimen changes as the crack propagates, which is related to the conservatism of the crack growth resistance curve. Therefore, it is necessary to identify the SENT test specimen usability and limitation via ductile damage simulations.

A new burst pressure model for thin-walled pipe elbows containing metal-loss corrosion defects

In this paper, a new burst pressure model for thin-walled pipe elbows containing metal-loss corrosion defects is developed based on a modified Goodall model for the burst pressure of intact elbows and the DNV model for the burst pressure of corroded straight pipes. The proposed model is validated using extensive parametric finite element analyses (FEA) and shown to be more accurate than two existing burst pressure models for corroded elbows reported in the literature. The accuracy of two well-known failure criteria used in FEA, i.e. the twice elastic slope (TES) and ultimate tensile strength (UTS) criteria are investigated. The UTS criterion is found to be more accurate than the TES criterion in determining the burst pressure of pipe elbows in FEA.

A strain-controlled fracture assessment for submarine thin-walled pipes with V-groove welds and circumferential embedded cracks

Abstract In the offshore industry, oil and gas are commonly transported with thin-walled clad pipes. Reel-lay is a widely used method to install clad pipes. During the installation and service process, engineering critical assessment (ECA) is usually required to guarantee safety. Most of the ECA methods pertain to surface cracks. The DNV-RP-F108 standard indicates that an embedded crack can be transformed into a surface crack in evaluation, and the result is still conservative. However, the evaluation can be over-conservative at times, meanwhile, the effect of the weld material as well as groove shape is not considered. In this work, a more direct assessment of welded clad pipes with a circumferential embedded crack is proposed based on a modified reference strain approach. A strain-controlled boundary condition is applied, and various pipe and weld geometrical shapes are considered in the analysis matrix. Two plugins based on Python script are developed to circularly create a lot of numerical models. Hundreds of regression analyses based on the linear relationship between normalized J integral and nominal strain are implemented. An analytical solution of the peak J integral of the embedded crack is proposed, and the solution is proved to be close to FEA.

Evaluation of Compression Performance of APM Aluminum Foam-Polymer Filled Pipes Prepared via Different Epoxy Resin Bonding Processes

The composite structurehttp://mts.hindawi.com/update/) in our Manuscript Tracking System and after you have logged in click on the ORCID link at the top of the page. This link will take you to the ORCID website where you will be able to create an account for yourself. Once you have done so, your new ORCID will be saved in our Manuscript Tracking System automatically."?> with aluminum foam not only has the strength and toughness of the dense material but also reduces the weight of the component and increases specific deformation energy absorption performance. In this paper, advanced pore morphology (APM) foam elements are combined with thin-walled circular steel pipes by epoxy-bonding and epoxy foam-bonding processes to prepare composite circular pipes. The direct epoxy-bonding process using epoxy resin refers to coating the surface of APM spheres, whereas the epoxy foam-bonding process involves the mixing of the epoxy resin with the epoxy foaming agent and then coating the surface of APM spheres with this mixed epoxy resin. The compression performances and energy absorption performances were analyzed by quasistatic compression tests. Results indicate that the different bonding modes change the deformation mode of the specimen under compression. The epoxy foam-bonding APM composite pipe has a higher compression load level than the epoxy-bonding APM filled pipe. The epoxy foam-bonding APM composite pipe is superior to the epoxy-bonding APM composite and thin-wall hollow pipe. Hence, the combination of foaming and bonding of epoxy can be used as a new filling process for APM fillers.

Numerical investigation of the transferability of ductile fracture behavior between thin-walled surface-cracked pipe, curved wide plate (CWP) and single edge notched tension (SENT) specimens

Numerical investigation of the transferability of ductile fracture behavior between thin-walled surface-cracked pipe, curved wide plate (CWP) and single edge notched tension (SENT) specimens

Limit load analysis of thin-walled as-fabricated pipe bends with low ovality under in-plane moment loading and internal pressure

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.

Investigation on the calculation model of burst pressure for tube and casing under practical service environment

The burst strength of tube and casing is important to the storage and development of hydrogen gas and natural gas. Studies on the current classic models to calculate burst pressure of tube and casing show that they are not suitable to predict the burst pressure of tube and casing under modern manufacturing technology level due to without considering the effects of radius-thickness ratio and practical service environment (capped-end condition and capped-open conditions). Hence, for the thin-wall (20＜D/t＜40) tube and casing, based on the deformation instability and finite strain theory, this paper has established the equations to calculate burst pressure of thin-wall pipe under capped-end condition and capped-open conditions by adopting the power-law constitutive relation. For the thick-wall (5 ≤ D/t ≤ 20) tube and casing, based on the failure criterion of through-wall yield, the unified algorithms of burst pressure for thick-wall pipe under capped-end condition and capped-open condition have been derived by adopting unified strength theory. The burst pressure model which can calculate the burst pressure of thick-wall pipe under modern manufacturing technology level, has been presented combining with weighting twin shear stress yield criterion. Numerical and experimental comparisons show that the calculated results of this equation are closest to the test data, and its accuracy and reliability are obviously superior to other models, and the service environment of tube and casing has a great impact on the burst pressure.

Transverse vibration of long offshore pipes

This paper has conducted a study of the transverse vibration of long vertically configured offshore pipes using the formulation developed by author [8], based on which a simple empirical formulation has been proposed. Numerical simulations have been carried out on the three representative size pipes, such as a thick wall pipe with radius of 50 mm with a wall thickness of 10 mm, a medium wall pipe with a radius of 0.2667 m with a wall thickness of 12.7 mm and a thin wall pipe with a radius of 0.305 m with a wall thickness of 6.3 mm with an axial length in a range of 100–10000 m. Finite element analysis has also been carried out to validate against the analytical results, which are in a very good agreement in particular for slender pipes.

Nonlinear stability analysis of thin-walled steel pipe confined in soft bilayer medium

This paper studies the structural stability of thin-walled cylindrical pipe surrounded by soft bilayer medium, subjected to uniform pressure. A two-dimensional (2D) finite element model (FEM) is developed by assuming a plane strain condition. Both the geometric and material nonlinearities are taken into account for the simulation. An elastic pipe confined in a uniform soft medium and bilayer medium is investigated, and the numerical results are compared with available closed-form analytical solutions. Then, the steel pipe with inelastic properties is investigated by tracing the pressure-displacement equilibrium paths of the crown position where the maximum radial displacement occurs. The pressure shows a significant drop after reaching the maximum level (critical buckling pressure). Furthermore, a geometric thickness parameter is introduced to define the border of the upper and bottom layer of the bilayer medium around the steel pipe. In addition, parametric studies show that the response of the steel pipe is significantly affected by the initial gap, the out-of-roundness imperfections, the deformable soft bilayer medium, and insensitive to the yield stress of inelastic pipe and the friction in the pipe-medium system. Finally, the present numerical results show close agreement with the experimental results for the inelastic confined pipe with an initial gap between the pipe and medium.

The influence of torsion effect on fracture behavior of Pipe Ring Notched Bend specimen (PRNB)

Through the time, researches realize the problem of inability to measure the fracture toughness of pipe material in some cases, because of inability of producing standard specimens from pipe wall. This problem is especially expressed in thin walled pipes. In that sense, a lot of alternative procedures and nonstandard specimens are proposed but with no notable success. One of the latest and the most convenient one is Pipe Ring Notched Bend specimen (PRNB) proposed by Gubeljak and Matvienko (Patent No. RU 2564696 C1, 10.10.2015.: Matvienko Y.G. and Gubeljak N., Model for Determination of Crack – Resistance of the Pipes). Lot of research are made on the PRNB specimen and this paper presents further analysis of such a specimen. Due to the specific geometry of PRNB specimen and loading which is three – point bending, torsion effect occurs in the region of crack. This paper deals with analysis of influence of this torsion effect on fracture behavior of PRNB specimen. In order to obtain more detailed analysis of torsion effect influence, J – integral versus thickness of the specimen curves are presented for the specimen with and without torsion effect and for various a/W ratios. Further, comparison of maximal J – integral values (at half of wall thickness B/2) for specimens with and without torsion effect in relation to the a/W ratio has been analyzed.