Hole Erosion Research Articles

Investigating concentrated leak erosion behaviour of cohesive soils by performing hole erosion tests

Internal erosion by piping is one of the common causes of failure of embankment dams and dykes. This phenomenon occurs when preferential flow paths develop in the earthfill or foundation; through these water flows, carrying away particles of soil and leading to the formation and the evolution of a continuous ‘pipe’ between the upstream and the downstream side. A series of hole erosion tests were conducted on cohesive soils in order to quantify critical shear stress and the coefficient of erosion: white kaolinite, proclay kaolinite and a hostun sand/proclay kaolinite mixture. The effects of compaction energy, moisture content, degree of saturation and the percentage of fines were investigated. The experimental results show that these parameters play a key role in the erosion characteristics. L’érosion de conduit est l’une des causes les plus fréquentes de rupture des barrages en remblai et digues. Ce phénomène se produit lorsqu’un chemin préférentiel d’écoulement se développe dans le remblai ou la fondation et à travers lequel l’eau s’écoule en arrachant et transportant les particules de sol à l’extérieur de l’ouvrage, conduisant ainsi à la formation et l’évolution continue d’un conduit entre l’amont et l’aval. Une série d’essais d’érosion de trou a été menée sur des sols cohérents afin de quantifier la contrainte critique d’érosion et le coefficient d’érosion: Kaolinite Blanche, Kaolinite Proclay et mélange sable d’Hostun/Kaolinte Proclay. L’influence de la teneur en eau, du degré de saturation, de l’énergie de compactage, et du pourcentage des fines a été étudiée. Les résultats expérimentaux montrent que ces paramètres jouent un rôle clé sur les caractéristiques d’érosion.

In vitro corrosion behavior of Ti-O film deposited on fluoride-treated Mg–Zn–Y–Nd alloy

In this paper, a new composite coating was fabricated on magnesium alloy by a two-step approach, to improve the corrosion resistance and biocompatibility of Mg–Zn–Y–Nd alloy. First, fluoride conversion layer was synthesized on magnesium alloy surface by immersion treatment in hydrofluoric acid and then, Ti-O film was deposited on the preceding fluoride layer by magnetron sputtering. FE-SEM images revealed a smooth and uniform surface consisting of aggregated nano-particles with average size of 100nm, and a total coating thickness of ∼1.5μm, including an outer Ti-O film of ∼250nm. The surface EDS and XRD data indicated that the composite coating was mainly composed of crystalline magnesium fluoride (MgF2), and non-crystalline Ti-O. Potentiodynamic polarization tests revealed that the composite coated sample have a corrosion potential (Ecorr) of −1.60V and a corrosion current density (Icorr) of 0.17μA/cm2, which improved by 100mV and reduced by two orders of magnitude, compared with the sample only coated by Ti-O. EIS results showed a polarization resistance of 3.98kΩcm2 for the Ti-O coated sample and 0.42kΩcm2 for the composite coated sample, giving an improvement of about 100 times. After 72h immersion in SBF, widespread damage and deep corrosion holes were observed on the Ti-O coated sample surface, while the integrity of composite coating remained well after 7d. In brief, the data suggested that single Ti-O film on degradable magnesium alloys was apt to become failure prematurely in corrosion environment. Ti-O film deposited on fluoride-treated magnesium alloys might potentially meet the requirements for future clinical magnesium alloy stent application.

Predicting initial erosion during the hole erosion test by using turbulent flow CFD simulation

CFD simulation with enhanced modeling of turbulence and near-wall treatment is used to model water–clay mixtures flowing through a cylindrical pipe domain. Effects on the wall-shear stress resulting from varying water clay content and applied hydraulic gradient are analyzed. Various parametric studies were performed and had shown that the two-dimensional modelling introduced in the present study does not yield a uniform wall-shear stress along the pipe wall and that clay concentration affects significantly the wall-shear stress value. This is in contrast with the common hypothesis used in one-dimensional modeling approaches where this stress is assumed constant and which gives rise to uniform erosion along the pipe wall. The obtained results had enabled predicting more realistically erosion amount and had allowed for understanding the irregular eroded hole wall shape as observed experimentally after performing the standard hole erosion test.

Energy-Based Method for Providing Soil Surface Erodibility Rankings

The jet erosion test (JET) and the hole erosion test (HET) are two tests used to determine soil erodibility classification, and results are commonly interpreted by two distinct methods. A new method based on fluid energy dissipation and on measurement of the eroded mass for interpreting the two tests is proposed. Different fine-grained soils, covering a large range of erodibility, are tested. It is shown that, by using common methods, the erosion coefficient and average critical shear stress are different with the JET and with the HET. Moreover, the relative soils classifications yielded by the two erodimeters are not exactly the same. On the basis of the energy method, an erosion resistance index is determined for both apparatuses, and a classification of surface-erosion resistance is proposed. For both apparatuses, values of the erosion resistance index are roughly the same for each soil, and a single classification of soil erodibility is obtained.

A Review of Cuttings Transport in Directional-Well Drilling

A Review of Cuttings Transport in Directional-Well Drilling This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 132372, “Review of Cuttings Transport in Directional-Well Drilling: Systematic Approach,” by T. Nazari, SPE, and G. Hareland, SPE, University of Calgary, and J.J. Azar, SPE, University of Tulsa, originally prepared for the 2010 SPE Western Regional Meeting, Anaheim, California, 27–29 May. The paper has not been peer reviewed. Hole cleaning during directional-well drilling is a major concern in the oil field and must be monitored and properly controlled during the entire drilling operation. Inadequate drilled-cuttings removal can cause many costly problems. Low annular-fluid velocity, lack of drillpipe rotation, and the wrong mud properties are primary factors in ineffective hole cleaning. The full-length paper presents a review of previous hole-cleaning studies and discusses an approach that is better suited for monitoring and controlling hole-cleaning problems. Introduction The rotary-drilling process consists of a rock-cutting tool (drill bit) upon which a downward force is applied [weight on bit (WOB)] and rotation (rev/min) is imposed. The drilled cuttings generated by the drill bit are removed by circulating a drilling fluid from surface to bottomhole and back to surface (cuttings transport) (Fig. 1). During directional-well drilling, cuttings removal becomes more difficult and if not controlled properly can result in serious problems such as mechanical pipe sticking (fishing or hole loss), excessive frictional torque (increase in rotary-power requirement) and frictional drag (inability to reach target), difficulty in landing casing, channeling problems during cementing, and difficulty in logging. The factors that are known to affect hole cleaning include annular eccentricity, inclination angle, drillpipe rotation, fluid flow rate (annular velocity and flow regime), rate of penetration (ROP), mud rheology and density, and cuttings (i.e., size, shape, and density). It is well documented that flow rate and drillpipe rotation have the most positive effect on hole cleaning. However, an increase in flow rate causes an increase in frictional pressure losses, which in turn causes an increase in equivalent circulating density (ECD), pump-pressure requirement, and potential hole erosion. An increase in pipe rotation can result in premature pipe fatigue failures caused by the induced cyclic stresses. Cuttings-Transport Problem In contrast to other industrial processes, the cuttings-transport problem in the drilling industry is more complex because of the many parameters that are interconnected nonlinearly. In simpler processes, some of the steps could be neglected. Comparing this scheme to a drilling process results in the following correlations: Process—drilling procedure Reference—ECD limitation, pump hydraulic-horsepower limitation, hole erosion, ROP limitation, geological-target limitation, rotary-power limitation Process inputs—flow rate, rev/min, hookload Process outputs—pressures, ROP, torque Internal states—WOB, eccentricity, hole cleaning Monitoring/control—lost circulation, drag, torque, cuttings returns, ROP, circulating standpipe pressure For a complete and reliable automated design process, the following steps must be taken: Signal measurements Monitoring of critical parameters Modeling Control

A Simplified Analytical Modeling of the Hole Erosion Test

Problem statement: Internal erosion occurs in soils containing fine particles under the action of high pressure gradients that could result from water discharge. This phenomenon can yield in its final stage to the formation of piping which constitutes a real threat for hydraulics infrastructures as it can precipitate their entire rupture in very short time. In order to mitigate this insidious hazard, it is important to characterize piping dynamics. In this context, the Hole Erosion Test was introduced to assess the erosive features of soils by means of two parameters, the erosion rate and the critical shear stress indicating the beginning of erosion. Modeling this test can enable to understand more comprehensibly the piping phenomenology. Approach: A simplified analytical modeling of the Hole Erosion Test was considered in this study. A closed form solution of erosion taking place during piping was derived without resorting to the habitual cumbersome developments that are needed to achieve complete solution of the rational equations describing this highly coupled problem. This was achieved by assuming formal analogy between the erosive shear stress and the friction shear that develops at a cylindrical piping wall under an axial viscous flow. The flow was assumed to be uniform along the tube. Results: A closed form analytical formula describing erosion dynamics associated to piping was derived. Theoretical predictions were compared with experimental results and the simplified model was found to predict accurately the increase of flow rate that results from piping erosion. Conclusion/Recommendations: The one-dimensional modeling that was proposed for the Hole Erosion Test under strong simplifying assumptions was found to yield the same features as those obtained in the literature by using other approaches. It gives furthermore the dynamics as function of the fluid regime existing inside the tube. In order to get further insight regarding the flowing flow action, which could be non uniform during erosion, more advanced modeling is needed.

Effect of Wall Roughness and Concentration of Clay on Erosion in the Hole Erosion Test

Problem statement: Internal soil erosion is a real threat for hydraul ic infrastructures. In its final stage it develops in piping involving the formation and progression of a continuous void inside the soil between the upstream and downstream sides. The hole erosion test was introduced to characterize kinematics of piping in terms of the t ime left to rupture. Actual modeling approaches of this test are essentially one dimensional. The wall shear stress generated by the flow is assumed to b e uniform, so that erosion rate is also uniform along the hole length. Experimental observations show however an irregular profile of the eroded hole. Approach: In this study an axisymmetric extension representation of the hole erosion test was perform ed. The biphasic flow at the origin of surface erosion occurring in the porous soil sample was modeled by means of the renormalization group based k-e turbulence equations. Fluent software package was used to perform the numerical modeling. Results: This had enabled to estimate the wall shear stress which was found to be non uniform along the hole length. Erosion rate was the n estimated by using a classical law. Its variation s as affected by the applied gradient pressure, fluid density as well as the actual fluid/soil interface roughness were analyzed. In particular, wall roughn ess and clay concentration were found to increase noticeably the erosion rate. Conclusion/Recommendations: Predicting erosion rate at the start of piping formation can be done by the propos ed model. Flow features are however very complex in the real HET configuration. In particula r, clay concentration does not vary equally along the hole length. The erosion law coefficients are v ariable. Transport phenomenon of some soils particles that detach is present in the problem. Fu rther investigations including these aspects should be performed in order to render more profoundly the complex physics involved in this experiment.

True Triaxial Piping Test Apparatus for Evaluation of Piping Potential in Earth Structures

Abstract Current methods available for testing the piping potential of soils in dams (pinhole test, hole erosion test, and slot erosion test) are limited to cohesive soils that maintain an open hole within the sample. These tests do not adequately simulate conditions within a zoned embankment, where zones of non-cohesive materials are present under relatively high confining stresses. A new apparatus, called true triaxial piping test apparatus or TTPTA, was developed for testing a wider variety of soils under a wider range of confining stresses, hydraulic gradients, and pore pressures than current tests allow. The TTPTA is capable of applying a range of confining stresses along three mutually perpendicular axes in a true triaxial test apparatus. Pore pressures are also controlled through regulated inlet and outlet pressures. The test determines the critical hydraulic gradient and, more importantly, the critical hydraulic velocity at which piping is initiated in non-cohesive soils. Detailed descriptions of the test apparatus and test method are presented, as are initial test results using TTPTA. Three sets of initial tests were conducted using uniform sand to (1) assess the repeatability of test results, (2) evaluate how the rate of change of inflow impacts the critical discharge rate at which piping is initiated, and (3) evaluate how the angle of seepage affects the critical velocity for piping initiation. These initial tests were conducted to evaluate the method and to help set test parameters for future testing. It is found that the TTPTA is capable of yielding fairly consistent results with 10 % scatter in repeat tests. The seepage angle tests demonstrate that the angle between seepage flow direction and the direction of gravity is an important factor to consider when evaluating piping potential. The rate of change in seepage also has a minor influence on test results, but a change in flow rate of 5 (mL/min)/min could produce reliable results. Based on the results, the hydraulic gradient is found to be a less reliable indicator of piping potential than the hydraulic velocity for non-cohesive soils. The TTPTA is capable of simulating conditions within small to medium sized embankments.

The scaling law in the hole erosion test with a constant pressure drop

AbstractA process called ‘piping’, which often occurs in the soil at dams, levees, and dykes, involves the formation and development of a continuous tunnel between upstream and downstream ends. The hole erosion test is commonly used to quantify the critical stress and the rate of piping erosion progression. The aim of this study is to draw up a model for interpreting the results of this test. A characteristic internal erosion time is defined and expressed as a function of the initial hydraulic gradient and the coefficient of surface erosion. It is established here that the product of the coefficient of erosion and the flow velocity is a significant dimensionless number: when this number is small, the kinetics of erosion are low, and the particle concentration does not have any effect on the flow. This finding applies to most of the available test results. Theoretical and experimental evidence is presented showing that the evolution of the pipe radius during erosion with a constant pressure drop obeys a scaling exponential law. Copyright © 2008 John Wiley & Sons, Ltd.

Corrosion behavior of composite brake materials

AbstractIt is very important to study the corrosion behavior of composite brake materials for their design, manufacture, and application. In the study, one kind of composite brake material used in engineering machinery, two kinds used in automobiles, and gray cast iron HT200 were selected as tested materials. Their corrosion behavior in typical acid solution, alkali solution, salt solution, running water, and air were investigated. The results showed that some components of composite brake materials, such as iron matrix, steel fiber, and iron powder, were easily subject to corrosion in acid solution. Corrosive pitting, net‐like cracking, and breakage appeared at their corrosion surfaces, and in the solution of 3.5% NaCl, corrosive pitting took place and corrosion holes of 2–8 µm diameter formed at the corrosion surface of these components. But when brake materials were exposed to the solution of 5% NaOH, the organic binder was corroded seriously, nearly parallel cracks formed at the corrosion surface and some samples even became loose powders because the corrosion makes the binder lose its adhering function. In running water and air, the tested samples have an excellent corrosion resistance, and the composite brake material containing organic binder has a better corrosion resistance compared with other tested materials. The investigation has also indicated that the interface between ingredients easily corrodes.

Simulated experiment evidences of the corrosion and reform actions of H2S to carbonate reservoirs: an example of Feixianguan Formation, east Sichuan

The reservoir of Feixianguan Formation of the Lower Triassic in the Sichuan Basin is the deepest buried carbonate reservoir in China, with developed secondary corrosion holes, high quantities carbonate reservoir, maximum effective carbonate reservoir thickness. Also Feixianguan gas reservoir has the highest quantities of H2S. Research discovers that there are close relationships between the formation of reservoir and H2S. The mutual actions between acidity fluid and carbonate promoted the forming of secondary carbonate holes. Through the experiment of corrosion of the samples of Feixianguan carbonate reservoir in saturated aqueous solution of hydrogen sulfide, the porosity and permeability increased greatly, porosity increased 2% and permeability increased nearly two quantity degrees, also the density became light, which confirm the corrosion and reform actions of H2S to carbonate.

Erosion Wear Characteristics and Mechanism of Si<sub>3</sub>N<sub>4</sub> Ceramics: Effect of Impact Angle

Erosion wearing regulation with different erosion angel for Si3N4 ceramics were systematically studied by liquid-solid dual phase erosion wearing test with rotation disk through comparing with Cr15Mo3 high chromium cast iron for pumps in industry. Besides the micro failure mechanism and the relationship between mechanical behavior and anti erosion wearing have been analyzed for the experimental materials. The experimental results were concluded as following: the erosion resistance of Si3N4 ceramic is about 20 times better than that of Cr15Mo3 high-Cr cast ion in erosion test angle, and the effect of erosion angel on the erosion wearing volume lose features as N-shaped curve with the biggest volume lose at 45° erosion angle while most erosion wearing volume at 90° angle, which indicates that it should avoid 45° or 90° erosion angle during materials designing. Obvious direction and erosion trace are revealed and volume lose mainly featured with tiny cutting, pear ditch and erosion hole, and micro crack and grain falling off at high angle erosion on the surface of Cr15Mo3 materials, besides smooth surface, high ductile, compact structure, fine grain and fine cylinder grain explaining main reason for excellent anti erosion wearing for Si3N4 ceramic.

An experimental investigation into the pressure - leakage relationship of some failed water pipes

This paper reports on an experimental study that was conducted to measure the leakage exponents of different types of leak openings (holes, corrosion holes, and longitudinal and circumferential cracks) and pipe materials (asbestos cement, mild steel and uPVC). A number of failed pipes taken from the Johannesburg water distribution system were tested, as well as a number of pipes with artificially induced leaks. The results of the study confirmed that leakage exponents can be significantly higher than the theoretical value of 0.5. While leakage exponents for round holes were close to 0.5, the values for corrosion holes varied between 0.67 and 2.30, for longitudinal cracks between 0.79 and 1.85, and for circumferential cracks between 0.41 and 0.52. Conclusions include that the highest leakage exponents were found in corroded steel pipes and that under certain circumstances, leakage exponents can be less than 0.5.

Study on Erosion Resistance of Structural Ceramics

The erosion resistance performances of high-Cr cast iron Cr15Mo3 and three kinds of structural ceramics, a-Al2O3, ZTA, Si3N4, were investigated in flowing suspensions of solid particles with a rotary disk erosion wear tester. The microcosmic failure mechanisms of their wear surfaces were analyzed. The results showed that the erosion resistance of Si3N4, ZTA, a-Al2O3 is 21.8, 8.2, 5.6 times than that of Cr15Mo3 respectively. For ceramic materials, toughness and strength are two main factors that affect erosion resistance rather than hardness. The wear rate of ceramic materials is in proportion to the strength and the biquadratic toughness. Due to erosion, Cr15Mo3 is worn out most in the whole, the erosion holes are very clear and its failure pattern is in “W” shape. The wear of ZTA and Al2O3 mainly occurs in the binding phase of the crystal boundary. Thus, the crystal grains are exposed, but without breaks and cracks. The failure pattern is in the shape of “U”. Si3N4 only loses some binding phase of the crystal boundary and the erosion surface is smooth.

Synthesis, characterization and hydrolytic degradation of linear and crosslinked poly[(glycino ethyl ester)(allyl amino)phosphazene

Polyorganophosphazenes substituted by glycino ethyl ester and allylamine with different ratios were synthesized and their structures were characterized by 1H NMR, 31P NMR and FTIR. Via the crosslink reaction, a novel biodegradable crosslinked polyorganophosphazene material was obtained. DSC and FTIR spectra indicated the occurrence of crosslink. Hydrolysis studies were also performed to compare the crosslinked polymers with linear ones. The co-substituted polyorganophosphazenes with more allylamine at pendant groups exhibited a lower degradation rate than poly[bis(glycino ethyl ester)phosphazene] and crosslinked polyphosphazenes had an even lower degradation rate. SEM photographs characterized the surface of polyphosphazenes films after hydrolytic degradation, confirming that uncrosslinked ones had outstanding hydrolytic evidences at the surface while the crosslinked ones only had sporadic small erosion holes, remaining much smoother.

On the modelling of piping erosion

A phenomenon called ‘piping’ often occurs in hydraulics works, involving the formation and evolution of a continuous tunnel between the upstream and the downstream sides. The hole erosion test is commonly used to quantify the rate of piping erosion. However, few attempts have been made to model these tests. From the equations for diphasic flow with diffusion, and the equations of jump with erosion, a piping model is developed. A characteristic time of internal erosion process is proposed. Comparison with experimental data validates our results. To cite this article: S. Bonelli et al., C. R. Mecanique 334 (2006).

Winter bat activity in the Canadian prairies

Periodic arousal from hibernation among mammalian hibernators is poorly understood. In bats, arousal is often associated with flight. We acoustically monitored two rocky areas along the Red Deer River in southeastern Alberta for bat activity in autumn, winter, and spring months. We found bats to be active in all months and at unexpectedly cold temperatures (coldest activity –8 °C). Bats were active even when ambient temperatures remained below 0 °C during the day and night. We documented Myotis ciliolabrum (Merriam, 1886), Myotis evotis (H. Allen, 1864), and Eptesicus fuscus (Beauvois, 1796) flying outside hibernacula in winter. Active E. fuscus that we captured in mid-winter of 2004–2005 weighed less than bats captured in the fall, but masses ranged from 14.0 to 21.0 g, indicating that some individuals still had fat reserves. Captured individuals were of various ages, with a male bias. Using radiotelemetry, we located the first natural rock-crevice hibernacula for male and female E. fuscus in the Canadian prairies. Winter roosts were narrow, deep rock crevices or erosion holes located in steep valley walls. We found evidence to suggest that dehydration may be a driving force for winter flights.

Effect of Different Abrasive Particle Hardness on the Erosion Resistant Performance of α-Al<sub>2</sub>O<sub>3</sub> Ceramics

The erosion resistance of α-Al2O3 ceramics in flowing suspensions of solid particles was investigated with a rotary disk erosion wear tester. The effect of different abrasive particle hardness on its erosion resistance was studied and the microcosmic failure mechanism of its surface was analyzed. The results show that the erosion resistance of α-Al2O3 is more and more excellent than that of the metal Cr15Mo3 with the hardness enhancement of the abrasive particles. When SiO2, Al2O3, SiC is in turn selected as the abrasive, the erosion resistance of α-Al2O3 ceramics is 4.06, 5.20, 5.77 times than that of Cr15Mo3 respectively due to the different hardness of such abrasives. Due to erosion, Cr15Mo3 is worn out most in the whole, the erosion holes are very clear and its failure pattern is in “W” shape. The wear of α-Al2O3 mainly occurs in the binding phase of the crystal boundary for its grain is fine and dense enough. So although the crystal grains are exposed at last, no breaks and cracks can be found on the erosion surface. Its failure pattern is in “U” shape.

Laboratory Tests on the Rate of Piping Erosion of Soils in Embankment Dams

Abstract The Slot Erosion Test and the Hole Erosion Test have been developed as fast and simple tests for studying the erosion characteristics of soil in cracks in embankment dams. The erosion characteristics are described by the Erosion Rate Index, which measures the increase of erosion rate with respect to an increase in the hydraulic shear stress; and the Initial Shear Stress, which represents the minimum hydraulic shear stress when erosion starts. Knowledge of these erosion characteristics aids in the prediction of the likelihood of embankment dam failure due to piping erosion in a risk assessment process. Values of the Erosion Rate Index span from 0 to 6, indicating that the changes in erosion rates in response to changes in hydraulic shear stress can differ by up to 106 times across different soils. The Erosion Rate Index is apparently influenced by the soil fines and clay-sized content, plasticity, dispersivity, water content, dry density, degree of saturation, clay mineralogy, and possibly the presence of cementing materials such as iron oxides. Coarse-grained, noncohesive soils, in general, erode more rapidly and have lower Initial Shear Stresses than fine-grained soils.

Investigation of Rate of Erosion of Soils in Embankment Dams

The slot erosion test and the hole erosion test have been developed to study the erosion characteristics of soil in cracks in embankment dams. The erosion characteristics are described by the erosion rate index, which measures the rate of erosion, and the critical shear stress, which represents the minimum shear stress when erosion starts. Values of the erosion rate index span from 0 to 6, indicating that soils can differ in their rates of erosion by up to 106 times. The rate of erosion is shown to be dependent on the soil fines and clay sized content, plasticity, and dispersivity; compaction water content, density and degree of saturation; and clay mineralogy, and possibly the presence of cementing materials such as iron oxides. Coarse-grained, noncohesive soils, in general, erode more rapidly and have lower critical shear stresses than fine-grained soils. Knowledge of the erosion characteristics of the soil in the core of an embankment dam aids in the assessment of the likelihood of dam failure due to piping erosion.