Plain Pipe Research Articles

Flow-induced oscillations of a cantilevered pipe conveying fluid with base excitation

It is known that a plain cantilevered pipe conveying fluid loses its stability by a Hopf bifurcation, leading to either planar or non-planar flutter for flow velocities beyond the critical flow velocity for Hopf bifurcation. If an external mass is attached to the end of the pipe (an end-mass), the resulting dynamics become much richer, showing 2D and 3D quasiperiodic and chaotic oscillations at high flow velocities. In this paper, a cantilevered pipe, with and without an end-mass, subjected to a small-amplitude periodic base excitation is considered. A set of three-dimensional nonlinear equations is used to analyze the pipe׳s response at various flow velocities and with different amplitudes and frequencies of base excitation. The nonlinear equations are discretized using the Galerkin technique and the resulting set of equations is solved using Houbolt׳s finite difference method. It is shown that for a plain pipe (with no end-mass), non-planar post-instability oscillations can be reduced to planar periodic oscillations for a range of base excitation frequencies and amplitudes. For a pipe with an end-mass, similarly to a plain pipe, three-dimensional period oscillations can be reduced to planar ones. At flow velocities beyond the critical flow velocity for torus instability, the three-dimensional quasiperiodic oscillations can be reduced to two-dimensional quasiperiodic or periodic oscillations, depending on the frequency of base excitation. In all these cases, a low-amplitude base excitation results in reducing the three-dimensional oscillations of the pipe to purely two-dimensional oscillations, over a range of excitation frequencies. These numerical results are in agreement with the previous experimental work.

Numerical investigation for the calculation of TiO2–water nanofluids' pressure drop in plain and enhanced pipes

In this investigation, a numerical model having two-dimensional equations was obtained by a CFD program and authors' experimental data were evaluated for the verification procedure of the numerical outputs. The experimental case study includes the single-phase flow of pure water in plain and micro-fin pipes whereas the numerical one has the simulated results of TiO2 particles suspended in single phase water flow in equivalent pipes at a constant heat flux. Hydrodynamics and thermal behaviors of the water–TiO2 flow were calculated by constant heat flux and temperature-dependent settings. Physical specifications of nanofluids were calculated by means of the results of authors' previous ANN analyses. This study illustrates local and average values of temperature, pressure, and velocity distributions in the tested pipes; furthermore, comparisons of pressure drop characteristics are given in terms of nanoparticle concentrations and tube types.

A Basis for Selecting the Most Appropriate Small Specimen Creep Test Type

Many components in conventional and nuclear power plant, aero-engines, chemical plant etc., operate at temperatures which are high enough for creep to occur. These include plain pipes, pipe bends, branched pipes etc., the manufacture of such components may also require welds to be inserted in them. In most cases, only nominal operating conditions (i.e., pressure, temperatures, system load, etc.) are known and hence precise life predictions are not possible. Also, the proportion of life consumed will vary from position to position within a component and the plant. Hence, nondestructive techniques are adopted to assist in making decisions on whether to repair, continue operating or scrap certain components. One such approach is to use scoop samples removed from the components to make small creep test specimens, i.e., sub-size uniaxial creep test specimens, impression creep test specimens, small punch creep test specimens, and small ring (circular or elliptical) creep test specimens. Each specimen type has its own unique advantages and disadvantages and it may not be obvious which one is the most appropriate test method to use. This paper gives a brief description of each specimen and associated test type and describes their practical limitations. The suitability of each of the methods for determining “bulk” material properties is described and it is shown that an appropriate test type can be chosen.

Buckling failure numerical analysis of HDPE pipes used for the trenchless rehabilitation of a reinforced concrete sewer

The first part of the paper presents a study of a buckling failure of an HDPE pipe of 1091mm in OD, which was applied for the trenchless non-structural rehabilitation of a leaky reinforced concrete sewer main of 1200mm in ID. The buckling failure occurred 1year after its installation. The paper deals with the problem, faced by an expert, who wants to find out the reasons for buckling of HDPE rehabilitation pipe some time after the failure occurred. The aim of the second part of this paper is to compare the analytical methods of checking buckling failure of plain pipes used in Europe (two German and one Scandinavian methods) in order to evaluate the discrepancies in the obtained results and their causes. The paper specifies other factors influencing the scale of discrepancies (different recommendations concerning the value of reduction coefficient, which included the influence of pipe deflection on the decrease of the critical buckling pressure value). Additionally it discusses factors, which should be considered when checking buckling requirement. As some manufacturers of HDPE pipes with profiled walls did not develop any nomograms allowing to define critical buckling pressure it was needed to check if those three procedures for checking the buckling requirement for plain HDPE pipes can be applied for HDPE pipes with profiled walls, which failed after some time. It was found out that the discrepancies of the obtained results are not so high to reject those methods. Many additional factors, which could have more significant influence than the type of the applied calculation method, were listed.

Experimental Investigation on Turbulent Flow Heat Transfer Enhancement in a Horizontal Circular Pipe using internal threads of varying depth

The present work focuses on Experimental investigation of heat transfer and friction factor characteristics of horizontal circular pipe using internal threads of pitch 100mm, 120mm and 160mm with air as the working fluid. The transitional flow regime is selected for this study with the Reynolds number range 7,000 to 14,000. The horizontal aluminum pipe was subjected to constant and uniform heat flux. The experimental data obtained were compared with those obtained from plain Horizontal pipe. The effects of internal threads of varying depth on heat transfer and friction factor were presented. Based on the same pumping power consumption, the pipe with internal threads possesses the highest performance factors for turbulent flow. The heat transfer coefficient enhancement for internal threads is higher than that for plain pipe for a given Reynolds number. The use of internal threads improved the performance of horizontal circular pipe. Keywords - Enhancement, internal threads, heat transfer and turbulent flow. I. INTRODUCTION Heat exchangers are used in different processes ranging from conversion, utilization & recovery of thermal energy in various industrial, commercial & domestic applications. Some common examples include steam generation & condensation in power & cogeneration plants; sensible heating & cooling in thermal processing of chemical, pharmaceutical & agricultural products; fluid heating in manufacturing & waste heat recovery etc. Increase in Heat exchanger's performance can lead to more economical design of heat exchanger which can help to make energy, material & cost savings related to a heat exchange process. The need to increase the thermal performance of heat exchangers, thereby effecting energy, material & cost savings have led to development & use of many techniques termed as Heat transfer Augmentation. These techniques are also referred as Heat transfer Enhancement or Intensification. Augmentation techniques increase convective heat transfer by reducing the thermal resistance in a heat exchanger. Use of Heat transfer enhancement techniques lead to increase in heat transfer coefficient but at the cost of increase in pressure drop. So, while designing a heat exchanger using any of these techniques, analysis of heat transfer rate & pressure drop has to be done. Apart from this, issues like long-term performance & detailed economic analysis of heat exchanger has to be studied. To achieve high heat transfer rate in an existing or new heat exchanger while taking care of the increased pumping power, several techniques have been proposed in recent years. Generally, heat transfer augmentation techniques are classified in three broad categories: active methods, passive method and compound method. A compound method is a hybrid method in which both active and passive methods are used in combination. The compound method involves complex design and hence has limited applications. M. Sozen and T.M. Kuzay numerically studied the enhanced heat transfer in round tubes filled with rolled copper mesh at Reynolds number range of 5,000-19,000. With water as the energy transport fluid and the tube being subjected to uniform heat flux, they reported up to ten fold increase in heat transfer coefficient with brazed porous inserts relative to plain tube at the expense of highly increased pressure drop. Q. Liao and M.D. Xin carried out experiments to study the heat transfer and friction characteristics for water, ethylene glycol and ISOVG46 turbine oil flowing inside four tubes with three dimensional internal extended surfaces and copper continuous or segmented twisted tape inserts within Prandtl number range from 5.5 to 590 and Reynolds numbers from 80 to 50,000. They found that for laminar flow of VG46 turbine oil, the average Stanton number could be enhanced up to 5.8 times with friction factor increase of 6.5 fold compared to plain tube. D. Angirasa performed experiments that proved augmentation of heat transfer by using metallic fibrous materials with two different porosities namely 97% and 93%. The experiments were carried out for different Reynolds numbers (17,000-29,000) and power inputs (3.7 and 9.2 W). The improvement in the average Nusselt number was about 3-6 times in comparison with the case when no porous material was used. Fu et al. experimentally demonstrated that a channel filled with high conductivity porous material subjected to oscillating flow is a new and effective method of cooling electronic devices. The experimental investigations of Hsieh and Liu reported that Nusselt numbers were between four and two times the bare values at low Re and high Re

Heat Transfer Enhancement Using Helical Pipes

The enhancement of laminar forced convection inside helical pipes is studied numerically and compared with plain pipes. The study is achieved numerically using the (Fluent-CFD 6.3.26) software program for solving the governing equations. The heat transfer coefficient and friction coefficient are calculated using the enhancement technique and compared with the plain tube. In this research the factors that affect the enhancement technique using helical pipes are studied, these factors are the ratio of (pitch /pipe length) (SL), Reynolds number and the heat flux applied to the external surface of the pipe. The results showed that there is an increasing in the heat transfer coefficient is related to the decreasing of (SL), increasing of Reynolds number and heat flux. The performance of the helical pipes is evaluated depending on the calculation of (Enhancement ratio), and it’s found that the enhancement ratio increases as Reynolds number increases and (SL) decreases. It is found that the best enhancement ratio was (200%) at (SR=0.05), (Re=2000),(Heat flux=3000W/m2).The results are compared with the literature and there is a good agreement.

Load bearing capacity of API X65 pipe with dent defect under internal pressure and in-plane bending

► Opening bending had a higher load bearing capacity than closing bending. ► TES moment decreased with increasing dent depths and internal pressures. ► Max moment in the closing bending mode increased with increasing internal pressures. The objective of this study was to investigate the effect of the dent magnitude on the collapse behavior of a dented pipe subjected to a combined internal pressure and in-plane bending. The plastic collapse behavior and bending moment of the dented pipe containing several dent dimensions were evaluated using elastic–plastic finite element (FE) analyses. The indenters used to manufacture the dents on the API 5L X65 pipe were hemispherical rods with diameters of 40, 80, 160 and 320 mm. Dent depths of 19, 38, 76, 114 and 152 mm were introduced to the pipe with a diameter of 762 mm and a wall thickness of 17.5 mm. A closing or opening in-plane bending load was applied to the dented pipes pressurized under an internal pressure equivalent to atmospheric pressure as well as pressures of 4, 8, and 16 MPa. The FE analyses results showed that the plastic collapse behavior of the dented pipes was significantly governed by the bending mode and the dent geometry. Moment-bending angle curves for the dented pipe were obtained from computer simulations and evaluated with a variety of factors in the FE analyses. The load bearing capacity of the dented pipes under the combined load was evaluated by TES (Twice Elastic Slope) moments. The load bearing capacity of the pipe containing up to a 5% dent depth of the outer diameter was not reduced in comparison to that of the plain pipe. The opening bending mode had a higher load bearing capacity than the closing bending mode under the combined load regardless of dent depth. The TES moment decreased with increasing dent depth and internal pressure regardless of the bending modes.

Fluid Jackets

To surround the circumference of plain concrete pipes with fluid jackets is a revolutionary concept that can result in maximum burial depths and live load capacities more than twice those of conventional, steel-reinforced concrete pipes. Moreover, the enhanced capacities are achievable with less than one-half the usual amount of concrete and with zero steel reinforcement. Alternatively, fluid jacketed concrete pipes may be designed with the same structural capacity as conventional reinforced concrete pipes but with a project cost savings that results from a 50% weight reduction per foot of pipe. These claims are supported by the analysis presented in this paper, which is a necessary first step before experimental validation can occur. Engineered plastic jackets encapsulate fluid (water) in a watertight configuration that encircles the buried concrete pipe. The encapsulated fluid transforms nonuniform soil pressure to uniform hydrostatic pressure around the pipe periphery. Consequently, the concrete pipe experiences hoop compression only, without the bending deformation and concrete cracking inherent in conventionally installed, reinforced concrete pipe. The fluid jacket concept has not been published in open literature. This paper illustrates the physics of the concept and presents the most promising configuration and materials determined through structural analysis studies with the CANDE-2007 computer program. Fluid jacket designs are proposed in this paper as a first step to bring this revolutionary idea to fruition. Next steps include laboratory testing, field testing, and modeling refinement.

Implementation of an unloading compliance procedure for measurement of crack growth in pipeline steel

As the demand for fossil fuels increases, pipelines are constructed in inhospitable areas. Underthese conditions, not only the strength but also the deformability of the pipelines becomes crucial. A strainbased design (SBD) procedure needs to be established. Traditional stress based approaches to evaluatedefect tolerance lead to conservative predictions. There is a need to accurately define the fracturetoughness of the pipeline steel and assess the criticality of weld defects under strain based conditions. Thispaper focuses on the implementation of the unloading compliance method to determine stable crackgrowth. The standardized test procedure described in ASTM E1820 is applied. This method is a handy toolto obtain the J-resistance curves which can forecast ductile failure in pipeline girth welds. Preliminaryexperiments have been performed on Single Edge Notch Bend (SENB) specimens of plain pipe metal.Using the implemented procedure, it was possible to obtain a good fit between calculated and measuredcrack size. The most important result is the smoothness of the calculated crack growth and the rathermonotonic increase of crack size. Since testing on SENB is well known to provide conservativemeasurements, Single Edge Notch Tension (SENT) specimens will be evaluated in future work

Thermally induced strains and stresses in cast iron water distribution pipes: an experimental investigation

Full-scale tests have been carried out on lengths of unrestrained and restrained plain and jointed distribution pipe sections (similar to 4 '' or similar to 100 mm internal diameter) in order to investigate the strains and loads generated in cast iron water distribution mains as a result of temperature fluctuations. Tests on unrestrained sections enabled the coefficient of thermal expansion of the pipe material to be measured. In a fully restrained situation, which can occur in a pipe section in service when the joints are locked, tensile stresses arise from a decrease in temperature ( in accordance with the predictions of a simple one-dimensional model) and it is shown that these stresses are sufficiently high to fracture a corroded pipe. In situations where the tensile stress leads to joint slippage, leakage through the joint is observed. Water leakage was also observed through the wall of corroded pipes that retained sufficient structural stability to carry load without failure.

Acoustic impedance at the interface between a plain and a perforated pipe

This paper considers the effective impedance that pertains as low frequency sound in a plain pipe radiates into a general perforated pipe of equal diameter. A previous theory that considered only the reactance is extended to also include resistance. Experimental measurements are made of the response of a Helmholtz resonator to an external sound field, where the neck of the Helmholtz resonator has both plain and perforated pipe sections. A complete theoretical model of this resonator allows for comparison between measured and predicted results of transfer functions from the external to internal sound fields of the resonator. The Nyquist plot of the admittance transfer function is extremely sensitive to the small resistance values, whereas the pressure transfer function gives more accurate results for resonant frequency and hence reactance than the usual method. In particular the results for resistance are so sensitive that it becomes possible to infer which of the current models for aperture resistance within the perforate is the most appropriate.

The application of PIV to the study of unsteady gas dynamic flow within pipes and at pipe discontinuities

This paper describes research using a pulse generator that provides discrete waves. The wave motion was recorded using a series of high speed pressure transducers and the ensuing movement of the gas particles within the pipes was recorded using digital PIV. Gas particle velocities of up to 250m/s were a regular occurrence and vortices of high angular velocity were a common problem with associated spin out of seed particles. Although flows were predominantly two dimensional, stereoscopic techniques were used to give optical access to otherwise inaccessible areas of flow. So far these techniques have been applied to the unsteady gas dynamic flow within plain pipes, at sudden expansions and contractions within pipes and at the end of a pipe open to the environment, both plain ended and when fitted with a bellmouth. Examples of all of these are presented in this paper.

Dynamics of cantilevered pipes conveying fluid. Part 1: Nonlinear equations of three-dimensional motion

In a three-part study, the first part being this paper, the investigation of the three-dimensional nonlinear dynamics of unrestrained and restrained cantilevered pipes conveying fluid is undertaken. The full derivation of the equations of motion in three dimensions for the plain cantilevered pipe is presented first in this paper, using a modified version of Hamilton's principle, adapted for an open system. Intermediate (between the clamped and free end) nonlinear spring constraints are then incorporated into the equations of motion via the method of virtual work. Furthermore, a point mass fixed at the free end of the pipe is also added to the system. The equations of motion are presented in dimensionless form and then discretized with Galerkin's method.

A comparative experimental investigation of concrete, reinforced-concrete and steel-fibre concrete pipes under three-edge-bearing test

Three-edge-bearing and crack size measurement tests were carried out on plain concrete, reinforced-concrete, and steel-fibre concrete pipes of 500 mm diameters. The average three-edge-bearing strength and crack size of steel-fibre concrete pipes having steel fibres of RC80/60-BN type at a dosage of 25 kg/m 3 turned out to be 82% greater and 47% smaller than those of plain concrete pipes, and 6% greater and 15% smaller than those of reinforced-concrete pipes, respectively. Tests on those steel-fibre concrete pipes having a steel fibres dosage of 40 kg/m 3 revealed that a steel fibres dosage of 25 kg/m 3 seems to be close to optimum because a 60% increase in the amount of steel fibres engenders only minor improvements. By these findings, steel-fibre concrete pipes are more economical than and mechanically and physically superior to reinforced-concrete pipes.

Water production by underground condensation of humid air

Condensation irrigation (CI) is a combined system for desalination and irrigation. By evaporating seawater in, for example, solar stills and letting the humidified air transport the formed vapour into an underground pipe system, fresh water will precipitate as the air is cooled by the ground. By using drainage pipes for underground air transportation, perforations in the pipes enable the water to percolate into the soil. This study of CI focuses on the transport of humid air inside buried plain pipes, where the condensed water stays inside the pipe and may thus be collected at the pipe endings and used for drinking. Numerical simulations of this system result in a mean water production capacity of 1.8 kg/m and day over a 50-m long pipe in a diurnally steady system, though shorter pipes result in a higher mean production. A performed theoretical analysis also indicates that CI is a promising alternative irrigation method as it enables the use of saline water for irrigation.

Use of life and strain fraction rules for creep life prediction of pressurized pipe components undergoing geometry change

The results of creep failure life predictions of pressurized plain pipes, pipe bends, and a thick-walled pipe with a circumferential weld are used to demonstrate the applicability of a stress-based life fraction rule (LFR) and a strain-based strain fraction rule (SFR), under conditions of geometric non-linearity (GNL). The material properties used are related to a CrMoV pipe, at 640°C. Both the LFR and the SFR predictions are based on the stress and strain solutions obtained from the finite element calculations using a Norton creep law. The results obtained were compared with those obtained from corresponding creep damage analyses. For the cases investigated, it has been shown that, compared with damage results, conservative failure lives with consistent failure positions were obtained for the pipe weld, using both the LFR and the SFR methods. For plain pipes and pipe bends, the SFR prediction produces conservative results. However, the LFR prediction overestimates the failure life for the range of pipe diameter ratios investigated. The results obtained indicate that the LFR and SFR methods have potential for predicting creep failure lives in cases when the effect of geometry change is significant and hence the method based on the steady state peak stresses obtained from small deformation analysis is not applicable.

The Effect of D/T on the Load Interaction Behavior of a Plain Pipe

The objective of the study is to determine the effect of diameter/thickness (D/T) ratio on the interaction of axial force, bending moment, torsion and internal pressure in plain pipes. The Tresca and von Mises criteria are used to determine the first yield behavior of pipes when subjected to combined loads. The results show that for certain load combinations, the load interaction behavior is affected by D/T ratio and some load interaction relations change with a load dominance. The general trend is an increase in effective stress as D/T is increased. Most design codes show slightly conservative pipe design.

High Temperature Behaviour of Materials and Components under Creep Conditions

This paper describes some recent work on the stress analyses and failure prediction of some typical pressurised high temperature components under creep conditions, including plain pipes, pipe bends, branch connections and welds etc, in the main steam pipework of power plant. The materials used are typically low alloy ferritic CrMoV steels. Experimental creep testing methods, and the procedures used for generating the material properties in creep and damage constitutive equations, are briefly described. Some typical numerical results are presented to illustrate the main characteristics of the behaviour of these components and to demonstrate the effects of geometry, material properties and loading modes on stress distributions and failure life predictions. The emphasis of the paper is on welded components.

Effect of geometry change on the creep failure life of a thick-walled CrMoV pipe with a circumferential weldment

The influence of the geometry change on the failure life during creep of an internally pressurised thick-walled main steam pipe with a circumferential weldment was investigated, using finite element creep damage analyses. The pipe is subjected to a realistic internal pressure and a range of end (system) load levels, which are within the limits allowed by design codes. Actual material properties were used which were obtained from creep testing for a CrMoV pipe weldment at 640 °C. Damage calculations were conducted to investigate the deformation and strain behaviour and to obtain the failure life of the welded pipe. The plain pipe behaviour obtained previously is briefly reviewed. The results obtained from the welded pipe are compared with those obtained from the corresponding plain pipe. For the particular weldment properties used, the results obtained show that the life reduction, due to geometry change, for the welded pipe, is in the range 4.6–6.1%, which is much less significant than that for the corresponding plain pipe. The practical significance of these results is discussed.

Effect of geometry change on the creep failure life of a thick-walled CrMoV pipe with a circumferential weldment

The influence of the geometry change on the failure life during creep of an internally pressurised thick-walled main steam pipe with a circumferential weldment was investigated, using finite element creep damage analyses. The pipe is subjected to a realistic internal pressure and a range of end (system) load levels, which are within the limits allowed by design codes. Actual material properties were used which were obtained from creep testing for a CrMoV pipe weldment at 640 °C. Damage calculations were conducted to investigate the deformation and strain behaviour and to obtain the failure life of the welded pipe. The plain pipe behaviour obtained previously is briefly reviewed. The results obtained from the welded pipe are compared with those obtained from the corresponding plain pipe. For the particular weldment properties used, the results obtained show that the life reduction, due to geometry change, for the welded pipe, is in the range 4.6–6.1%, which is much less significant than that for the corresponding plain pipe. The practical significance of these results is discussed.