Pipe Invert Research Articles

Experimental investigation of coarse particle conveying in pipes

The advanced knowledge of particle-water mixture flow behaviour is important for safe, reliable, and economical design and operation of the freight pipelines. The effect of the mixture velocity and concentration on the coarse particle - water mixtures flow behaviour was experimentally investigated on an experimental pipe loop of inner diameter D = 100 mm with horizontal, vertical, and inclined pipe sections. Narrow particle size distribution basalt pebbles were used as model of coarse-grained solid particles. The radiometric method was used to measure particle concentration distribution in pipe cross-section. Mixture flow behaviour and particles motion along the pipe invert were studied in a pipe viewing section. The study revealed that the coarse particle- water mixtures in the horizontal and inclined pipe sections were significantly stratified. The particles moved principally in a layer close to the pipe invert. However, for higher and moderate flow velocities the particles moved also in the central part of the pipe cross-section, and particle saltation was found to be dominant mode of particle conveying.

Experimental investigation of coarse particles-water mixture flow in horizontal and inclined pipes

Abstract The effect of solid concentration and mixture velocity on the flow behaviour, pressure drops, and concentration distribution of coarse particle-water mixtures in horizontal, vertical, and inclined smooth stainless steel pipes of inner diameter D = 100 mm was experimentally investigated. Graded basalt pebbles were used as solid particles. The study revealed that the coarse-grained particle-water mixtures in the horizontal and inclined pipes were significantly stratified. The solid particles moved principally in a layer close to the pipe invert; however for higher and moderate flow velocities, particle saltation became the dominant mode of particle conveyance. Frictional pressure drops in the horizontal pipe were found to be markedly higher than in the vertical pipe, while the frictional pressure drops in the ascending pipe increased with inclination angle up to about 30°.

Solid velocity and concentration fluctuations in highly concentrated liquid–solid (slurry) pipe flows

Solid velocity and concentration fluctuations were measured for concentrated sand-water mixtures (20–35% solid by volume) in horizontal pipe flow using Electrical Impedance Tomography (EIT). Narrowly sized sand (d50=100μm) was used to prepare each slurry tested in a 52mm (i.d.) horizontal pipe loop at mixture velocities (2–5m/s) that were significantly above the deposition velocity. The EIT measurements were used to obtain solid velocity and concentration fluctuation maps. Results show that the magnitude of the local solid concentration fluctuations is greater near the pipe wall and increases as the mixture velocity increases. Additionally, the concentration fluctuations are greater near the pipe invert, particularly at lower mixture velocities and/or concentrations where the solid concentration profiles are asymmetric. The Fast Fourier Transform (FFT) method was employed to study the power spectral density of these fluctuations. This analysis indicates that concentration fluctuations are produced almost entirely by particle–fluid turbulence interactions, rather than through particle–particle or particle–wall interactions. Comparison of the particle diameter with the characteristic turbulent length scales shows that the particles interact with turbulent eddies in the dissipative range, which is in accordance with the power spectral density analysis. The findings presented here are consistent with previous studies of fluidized beds and gravity-driven flows.

A three-dimensional analysis of the effects of erosion voids on rigid pipes

In this study, elasto-plastic finite element analyses are performed to investigate the three-dimensional effects of erosion voids developing behind the walls of an existing sewer pipe on the earth pressure distribution around the pipe and the stresses in the pipe wall. Initial earth pressures are first calculated and compared with field measurements. Erosion voids of different sizes are then introduced at the springline and invert of the pipe and the changes in pressure are evaluated and compared with the initial values. The effects of increasing the void length, depth and angle are examined. Results clearly reveal that the presence of erosion voids can have a significant impact on the earth pressure distribution around an existing pipe as well as on the pipe wall stresses. Increase in pressure is found to be mainly influenced by the void length and location with respect to the pipe circumference. Voids introduced at the springline resulted in earth pressure increase of more than 100% near the void boundaries whereas the pressure change was less significant when the void is introduced at the pipe invert. The findings of this study highlight the importance of locating voids behind pipe walls to prevent further deterioration and possibly sewer failure.

Interaction between catenary riser and soft seabed: Large-scale indoor tests

Nowadays, steel catenary riser (SCR) has become the most favorable method for oil and gas transportation in deep water. Accurate analysis of riser fatigue is heavily dependent on the interaction between riser and the seabed soil, which is a research focus in recent years. This paper aims to simulate the 3D interaction between SCR and typical clay seabed through large-scale indoor tests in 1g condition. The dynamic pipe•soil interaction is modeled through applying cyclic motion at one end of the pipe. The trench formation, pipeline behavior and the excess pore water pressure beneath the pipe invert are all analyzed in detail.The apparently dynamic embedding process and the ladled shape trench at touchdown zone (TDZ) were observed, which can be attributed to soil softening. The suction at the pipe/soil interface was captured and the accumulation of excess pore pressure was visualized. The results based on this study indicate that: the excess pore water pressures at different positions along the pipe axis vary with different trends, which may be attributed to their corresponding pipe trajectories. Therefore the accurate loading history simulation is very important for conventional 2D plane strain tests. It is found that, after 200 cycles, the maximum dynamic embedment factor fdyn along the axis of the model riser was up to 1.6, the pipe embedment depth increased by up to 60% and the average bending moment increased by up to 31.0%.

Fully Stratified Particle-Laden Flow in Horizontal Circular Pipe

This article describes the results of an experimental measurement and visualization of coarse-grained fully stratified particle-water mixtures. This article focuses on the study of the carrier liquid velocity field and behavior and local velocities of conveyed particles. Glass balls and graded pebble gravel of 6 mm mean diameter were conveyed by water in a horizontal smooth pipe loop with a transparent pipe viewing section of inner diameter 40 mm. The measurements were performed in the smooth pipe and the pipe with rough stationary bed created by two layers of spherical particles of the same mean diameter as the conveyed particles. Particle movement along the pipe bottom was studied and the effect of the stationary bed on local velocity values of the carrier liquid and conveyed particles were evaluated. It was concluded that in the flow with stationary bed the maximum liquid velocity is markedly shifted from the pipe center to its top. The coarse-grained particles moved principally in a layer close to the pipe invert, for higher flow velocities particle saltation becomes the dominant mode of transport.

Bed Load Erosion Patterns and Their Effect on the Structural Strength of Rigid Pipes Made of Homogeneous Materials

This manuscript concerns the decrease of the structural strength of rigid pipes made of homogeneous materials due to bed load erosion, caused by different concentrations of hard solid particles transported by the sanitary sewage, or surface runoff. Such a phenomenon has been observed in combined sanitary systems (CSS), as well as in force mains delivering domestic sewage due to the penetration of hard solid particles into the sanitary sewerage system. Field observations have indicated that the low concentrations of solid particles transported with the sewage lead to the formation of a groove at the pipe invert. Experiments carried out in this study have shown that the width of the groove mainly depends on the concentration of the solid particles. Numerical simulations have indicated that bed load erosion resulting from very low concentrations of solid small particles may be more detrimental to the structural strength of the pipe than higher concentration of such particles.

Study of non-uniform bedding support under continuous PVC water distribution pipes

Current design standards for buried pipe installations assume that loading and bedding conditions along pipes are uniform, and thus do not take into account the effect of soil variability. However, although careful attention may be paid during pipe installation, there is still a possibility that a pipeline may experience non-uniform loading or bedding conditions during its lifetime, which may lead to pipe failure. Thus, these conditions should be addressed to understand the implications of construction practice and problems that may be detected after construction. In this paper, a parametric study employing three-dimensional finite element analysis is used to examine a continuous PVC water pipe. The objective is to understand the effect of non-uniform bedding support on the stability of buried PVC pressure pipes, and the longitudinal soil–pipe interaction. The numerical analyses are performed using ABAQUS. The results of the finite element analyses demonstrate that pipes with discontinuous bedding experience stresses higher than those with uniform ground support (37–69% higher for medium dense sand, and 45–95% higher for dense sand bedding), and that it is better to achieve uniform soil support under the pipe invert than to achieve non-uniform support in high stiffness (highly compacted) bedding (results that support conventional wisdom where a layer of uncompacted bedding is used under the invert in preference to well compacted bedding that is not level). The analysis also indicates that it is more important to achieve that uniform support under the invert than dense soil backfill under the haunches.

External corrosion to concrete sewers: a case study

The aim of this study was to investigate the deterioration of concrete sewers and identify responsible factors; this investigation was a part of an ongoing asset evaluation for Rennes (France). The sewer studied was a 300 mm spun concrete pipe laid in 1992. Core samples (D 28 mm, L 40 mm) were taken from different areas of a pipe (invert, crown and side wall) and analysed to quantify the condition of the concrete and the extent of damage to the internal and external surface of the pipe. Physical and mechanical properties of the material were characterised. The depassivation of the concrete was measured by testing with a phenolphthalein solution. The study showed that in this particular case the external corrosion was extensive with minimal internal corrosion. It is proposed that the corrosion was possibly linked to the use of a contaminated backfill or organic acids in the ground water. Recommendations are proposed concerning the direction of future research.

Flow Structure of Coarse-Grained Slurry in A Horizontal Pipe

Flow Structure of Coarse-Grained Slurry in A Horizontal Pipe The flow behaviour of coarse-grained slurry depends on particle size, shape, density and concentration, and on the density and rheological properties of the carrier liquid. The present paper describes the results of an experimental investigation and flow visualisation of model coarse-grained particle-water mixtures in a closed pipe loop with smooth stainless steel pipes of inner diameter 36 mm. Glass balls and washed graded pebble gravel of mean diameter d50= 6 mm were used as model coarse-grained material. The effect of slurry velocity and particle concentration on the slurry flow behaviour and pressure drop in the turbulent regime was evaluated. Particle distribution in the pipe cross-section and motion of particles along the pipe invert, particle saltation and particle conveying in the carrier liquid were investigated in a transparent pipe viewing section and motion of individual particles was described. Velocity profiles of the carrier liquid and conveyed particles were determined.

Development of a Depth‐Integrated Sample Arm to Reduce Solids Stratification Bias in Stormwater Sampling

A new depth-integrated sample arm (DISA) was developed to improve the representation of solids in stormwater, both organic and inorganic, by collecting a water quality sample from multiple points in the water column. Data from this study demonstrate the idea of vertical stratification of solids in storm sewer runoff. Concentrations of suspended sediment in runoff were statistically greater using a fixed rather than multipoint collection system. Median suspended sediment concentrations measured at the fixed location (near the pipe invert) were approximately double those collected using the DISA. In general, concentrations and size distributions of suspended sediment decreased with increasing vertical distance from the storm sewer invert. Coarser particles tended to dominate the distribution of solids near the storm sewer invert as discharge increased. In contrast to concentration and particle size, organic material, to some extent, was distributed homogenously throughout the water column, likely the result of its low specific density, which allows for thorough mixing in less turbulent water.

Remarks on Camp’s Criterion for Self-Cleansing Storm Sewers

This study brings to the attention the difficulty imposed by the design on the development of a self cleansing storm sewer based on a general rule of minimum water velocity of 0.75 m/s under pipe full capacity and suggests the Camp’s criterion as an alternative. The key finding is the determination of the lower limit of flow strengths above which the Camp’s criterion can be applied to warrant the development of a more efficient storm sewer system. The lower limit is adjusted for storm sewers with loose or rigid boundary serving two transport conditions: to sustain equal sediment mobility on pipe invert instead of selective transport, and to avoid progressive deposition of finer grains due to low and reducing water flows.

The hydraulic transportation of thickened sludges

Industries which pump sludges are under continuous pressure to decrease water content, and increase concentration. Environmentally superior disposal techniques are demanding that such sludges have high mechanical strength properties. This results in a sludge with an increasing viscous character. At high concentration, the viscous forces – which are usually highly non-Newtonian and yield stress in nature – become dominant, and flows inevitably become laminar. The objective of this paper is to demonstrate the effect and evaluate the impact that increasing non-Newtonian viscous stresses – particularly yield stress – have on the pipelining problem. An industrially relevant sludge pipe flow study is presented, demonstrating and quantifying the relationship between sludge rheology and flow regime. It is argued that laminar flow will result in settlable solids accumulating on the pipe invert, leading to pipe blockage. Although some practical remedies have been proposed, this problem requires urgent and focussed research.. Water SA Vol. 30 (5) 2005: pp.66-68

Flume for Teaching Spatially Varied Open-Channel Flow

Spatially varied flow in open channels is a topic that is often included in undergraduate open channel hydraulics courses. Physical and computational models are developed to enhance the presentation of spatially varied flow to engineering students at the late undergraduate or early graduate level. The physical model is inexpensive and easy to build and the computational model is easily developed using commercially available spreadsheet software. The physical model consists of a 30.48 cm nominal-diameter PVC pipe that is 6.1 m in length and has circular orifices approximately 1.40 cm in diameter drilled on 15.24 cm centers along the pipe invert. A relationship between the orifice discharge coefficient and a modification of the Froude number, as measured in the flume upstream of the orifice in question, was developed in repeated trials having varying flume slope, volumetric inflow rate, and end conditions. With this relationship, a stepwise solution to the energy equation is used to predict the water surface profile. Differences between the water surface profiles observed and predicted in repeated trials averaged approximately 2 mm.

Numerical modelling of bed load sediment traps in sewer systems by density currents

A model with density currents has been developed and tested to simulate bed load sediment traps. In this model, the bed load layer over the pipe invert is considered as a continuous layer characterised by a density and a viscosity which depends on the solid concentration. A set of equations has been established that describes the trapping of the bed load material as the dynamics of two non-miscible fluids over and in the bed load sediment trap. The Fluent package has been used and adapted to solve the equations of the model. The VOF method (Volume Of Fluid) has been chosen to solve the two phase approach according to a Euler-Euler scheme. Several series of simulations have been carried out in order to assess the influence of the slot position and trap design on efficiency. The results obtained agree with previous empirical findings, and allow confirmation (in a more reliable manner than before) that the best sediment trap design involves a centrally-placed slot with the two plates covering the trap reservoir placed at the same height as one another.

Numerical modelling of bed load sediment traps in sewer systems by density currents

A model with density currents has been developed and tested to simulate bed load sediment traps. In this model, the bed load layer over the pipe invert is considered as a continuous layer characterised by a density and a viscosity which depends on the solid concentration. A set of equations has been established that describes the trapping of the bed load material as the dynamics of two non-miscible fluids over and in the bed load sediment trap. The Fluent package has been used and adapted to solve the equations of the model. The VOF method (Volume Of Fluid) has been chosen to solve the two phase approach according to a EulerEuler scheme. Several series of simulations have been carried out in order to assess the influence of the slot position and trap design on efficiency. The results obtained agree with previous empirical fmdings, and allow confirmation (in a more reliable manner than before) that the best sediment trap design involves a centrallyplaced slot with the two plates covering the trap reservoir placed at the same height as one another.

Coarse-particle pipeline transport: Effect of particle degradation on friction

When coarse particles are transported in pipes, mechanical friction occurs near the pipe invert, and hence large pressure gradients are required. This behaviour is described by the sliding-bed model, from which an approximate expression for the solids effect has been derived. Pilot-plant tests were carried out with coarse gravel in a large recirculating pipe loop. Initially, all particles were larger than 10 mm in diameter, and the solids effect was in good accord with the equation derived from the sliding-bed model. However, as the testing continued the particles degraded, and the pressure gradient diminished significantly. It was seen how the solids effect changes with exposure time or, equivalently, with the number of passes through the pump.

SPIDA Method for Reinforced Concrete Pipe Design

The required supporting strength of a buried pipe is affected by the total load imposed upon the pipe and the manner in which the pipe is supported by the surrounding soil. The classic procedure for designing reinforced concrete pipe is the indirect design method, which is based on: (1) Determining the moment that will occur at the pipe invert under the specified loading conditions; (2) determining a three‐edge bearing load or D‐load that produces the same moment; and (3) designing the pipe reinforcing for that D‐load. Direct design methods determine the actual moments, thrusts, and shears in the entire buried pipe and they design the reinforcing to carry these forces. The advent of finite element modeling of soil behavior now allows an even more direct design method in which the actual soil conditions around a pipe are accurately modeled. This paper will demonstrate the differences between the various design methods by analyzing an actual installation with both methods. The finite element analyses are co...