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Wear 267 (2009) 259–263

Contents lists available at ScienceDirect

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hort communication

xperimental technique to analyse the slurry erosion wear due to turbulence

arendra M. Dube ∗, Anirudh Dube, Deepak H. Veeregowda, Suman B. IyerUCOM Instruments (P) Ltd., # 477/A, 4th Phase, Peenya Industrial Area, Bangalore - 560 058, India

r t i c l e i n f o

rticle history:eceived 5 September 2008eceived in revised form 16 February 2009

a b s t r a c t

Erosion due to turbulence is a predominant factor in plant design for slurry handling. DUCOM Instru-ments (P) Ltd. has built a “counter rotating double disc erosion tester” to analyse surfaces for erosiondue to turbulence. Volume loss of Stainless Steel and aluminum as a function of varying time, particle

ccepted 16 February 2009

eywords:rosionorrosionurbulencelurry

hardness, speed and slurry concentration is evaluated in this erosion tester. Individual study on the effectof corrosion on the total volume loss is conducted and found to be high in alumina slurry and low in silicaslurry.

© 2009 Elsevier B.V. All rights reserved.

ounter rotating double disc erosion tester

. Introduction

There have been theories on plant design for slurry handling1]. Erosion in general is due to two complementary phenomena,ike cutting and deformation. It is a function of particle shape,ensity, hardness, concentration and the nature of target mate-ials. The correlation between all these parameters on predictionf the wear is explained in ref. [2]. Developing surface coatingsr alloying materials for resisting erosion wear has been possibleue to various erosion test rigs: such as jet impingement tester3], Coriolis erosion tester [4], and pot tester [5]. All the aboveesters were used with laminar flow and the erosion due to tur-ulence was not a concern. For example, the flow of a fluid downstraight pipe provides an example of a shear flow undergoing a

udden transition from laminar flow to turbulence at bends. Study-ng the slurry behaviour in turbulence is in progress to improvehe process efficiency in hydro-transport plants in mineral process-ng industries. The importance of the erosion due to turbulences missing, and needs to be understood for efficient plant design.he effect of erosion on corrosion kinetics and corrosion on therosion behaviour has been observed in many research papers.his synergetic effect on wear is also evaluated using this newester.

The efforts are made by DUCOM to develop a counter rotatingouble disc erosion tester, to study the effect of slurry turbulencen wear (erosion and corrosion).

∗ Corresponding author. Tel.: +91 80 40805555; fax: +91 80 40805510.E-mail address: nmdube@ducom.com (N.M. Dube).

043-1648/$ – see front matter © 2009 Elsevier B.V. All rights reserved.oi:10.1016/j.wear.2009.02.013

2. Counter rotating double disc erosion tester

There are two discs placed co-axially and rotated at equalrates in opposite direction. The arrangement is shown in Fig. 1.There are two induction motors with a drive to control the speedbetween 0–3000 rpm. The co-axial discs are fixed using a jobholder at the end of each of the motor shaft. The co-axial counterrotating discs are placed in the slurry chamber. The discs of diam-eter 160 mm and thickness of 2 mm can be accommodated inthe slurry chamber. The slurry chamber is equipped with leakproof sealing to avoid spillage. The distance between the discscan be varied to generate the turbulent regime in the slurrychamber.

3. Slurry flow between counter rotating disc

The flow of a fluid between the counter rotating discs isdescribed by two theories, as explained below.

• When the discs rotate in opposite directions at same angular rate,there is an existence of a thin transition layer or internal boundarylayer midway between the discs. On either side of this transitionlayer the angular velocity of the fluid is equal and opposite withthe magnitude less than the disc [6].

• Based on Von Karman theory, flow between the counter rotating

discs has an angular velocity equal to zero at the centre and hasboundary layers near the walls [7,8].

In the following research the slurry is of dense medium andis assumed to behave like a Newtonian fluid. The slurry contains

260 N.M. Dube et al. / Wear 267 (2009) 259–263

Nomenclature

C volumetric concentration of the slurryds diameter of the slurry particlesr* disc aspect ratioro radius of the discRe rotating Reynold numbers distance between the discswi initial weight

Greek lettersı average distance between the slurry particle�s density of the silica particles�L density of the liquid�m density of the slurry�m kinematic viscosity of the slurry�L kinematic viscosity of the liquid˝ angular rate of the disc

mfl

r

ı

(

�

�

ib

R

Table 2Properties of water based slurries with C = 40%, r* = 10 and ˝ = 25.16 mm/s.

Slurry type ı (�m) �m (g/cm3) �m (mm2/s) Re

Silica slurry 7.23 2.06 5.58 1152Alumina slurry 7.23 2.68 4.23 1519

TM

M

ASSA

Fig. 1. Counter rotating double disc erosion tester.

onodispersed particles and can be modelled like any Newtonianuid [9].

The average distance between the particles in the slurry envi-onment is calculated by Eq. (1) [10].

=[(

Clim

C

)1/3

− 1

]ds (1)

The kinematic viscosity and density of the slurry is given by Eqs.2) and (3) [11].

m = �L

(�L

�s

)(1 + 2.5C + 10C2 + 0.0019e20C ) (2)

m = �sC + �L(1 − C) (3)

The fluid motion in the counter rotating discs can be character-

zed by the rotational Reynolds number and aspect ratio as giveny Eqs. (4) and (5) [12].

e = ˝s2

�s(turbulence regime at Re > 750) (4)

able 1echanical properties of disc materials and slurry particles.

aterial Yield strength (MPa) Young’s modulus (GPa)

luminum 48 79S-304 170 190ilica particle –lumina particle –

Fig. 2. Eroded Al disc.

re = ro

s(5)

4. Experimental details

The mechanical properties of stainless steel, aluminum, silicaand alumina particles are given in the Table 1. The flow propertiesof slurry in the counter rotating discs are defined using the Eqs.(1)–(5) and displayed in Table 2.

Tests were carried out with silica or alumina slurry and alu-minum and stainless steel discs. As per the flow propertiesmentioned in Table 2, volume loss of disc material was measured atconstant particle concentration (40%) of the silica slurry and varyingtime (0.5–3 h: in steps of 0.5 h) and angular rate (1000–3000 rpm:in steps of 200). The same pattern of test was repeated by varyingthe silica concentration (14–55%: in steps of 7%) and keeping theangular rate (25 mm/s or 1500 rpm) and time constant (1 h). Forevery test in each parameter, new discs and slurry were used toensure the fresh surface and particles for erosion.

To study the effect of corrosion on wear [13–15] we used a nitro-gen purge and oxygen sensor (Marathonmonitors-USA). This setupand study is based on an assumption that the corrosive wear is pro-portional to oxygen content in the environment [14]. The nitrogenpurge used in this set-up is similar to the food packing industries.The flow rate of the nitrogen gas was controlled for 20 ppm oxy-gen content in the environment. The effect of corrosion on the totalvolume loss due to turbulence, particle hardness, particle concen-tration and time was studied in this set-up.

5. Results and Discussion

The eroded samples are displayed in Figs. 2 and 3; the regionexposed to erosion (turbulence) has a different intensity compared

Hardness Size (�m) Density (g/cm3)

201 BHN – 2.71245 BHN – 7.881000 kg/mm2 50 2.652000 kg/mm2 50 3.97

N.M. Dube et al. / Wear 267 (2009) 259–263 261

Fig. 3. Eroded SS-304 disc.

tt(rpa

in the angular rate increases the turbulence, as per Eq. (4). Fig. 5shows an increase in the wear as a function of time and, a similarprofile is seen by varying the particle concentration as shown inFig. 6.

Fig. 4. Wear (cm3) vs. disc angular rate (weight fraction).

o the non-eroded samples. Green (×) and red (+) colour represents

he silica and alumina particles, respectively. Black (—) and blue—) colour represents the stainless steel (grade 304) and aluminum,espectively. The green (×) on black (—) plot determines the silicaarticle erodent on the stainless steel target material. Fig. 4 showsn increase in the wear as a function of the angular rate. The increase

Fig. 5. Wear (cm3) vs. time (h).

Fig. 6. Wear (cm3) vs. particle concentration (weight fraction).

Fig. 7. Wear (cm3) vs. angular rate (rpm) with nitrogen atmosphere (a) Aluminumdisc (b) SS-304 disc.

262 N.M. Dube et al. / Wear 267 (2009) 259–263

Fs

ttpmswrcioctda

e

ig. 8. Wear (cm3) vs. slurry concentration (weight fraction) with nitrogen atmo-phere (a) Aluminum disc (b) SS-304 disc.

Reduced oxygen content in the environment has an effect onotal wear [13–15] as observed in this study. Figs. 7–9 illustrateshe change in the wear rate due to corrosion. The yellow lineresents the wear under reduced oxygen content in the environ-ent, which could be due to reduced corrosion activity in the

ystem. Fig. 7(a), 8(a) and 9(a) represent the synergistic effect onear of the aluminum disc due to silica and alumina slurry envi-

onment. At high angular rates (above 2000 rpm), the effect oforrosion is higher in alumina slurry environment compared to sil-ca slurry, as seen in Fig. 7(a). Similarly there is a substantial effectf corrosion on aluminum disc due to alumina slurry environmentompared to silica slurry environment at increased particle concen-ration, as shown in Fig. 8(a). Effect of corrosive wear on aluminum

isc is negligible (except at 1.5 h), for both alumina and silica slurrys seen in Fig. 9(a).

Figures 7(b), 8(b) and 9(b) present the synergisticrosion–corrosion effect on wear of SS-304. In this case, at

Target type Slurry type Corrosion acti

Aluminum disc (commercial) Alumina slurry HighSilica slurry Low

SS-304 Alumina slurry HighSilica slurry Marginal

Fig. 9. Wear (cm3) vs. time (h) with nitrogen atmosphere (a) Aluminum disc (b)SS-304 disc.

angular rate above 2400 rpm, the corrosive wear is higher inalumina slurry compared to silica slurry as seen in Fig. 7(b). Asimilar trend is observed with increase in concentration or time asseen in Fig. 8(b) and Fig. 9(b).

The existence of the turbulence regime in counter rotatingdouble discs erosion tester is supported by the Reynolds number(Re > 750) [12]. The increase in turbulence is going to increase thewear in counter rotating erosion tester, designed by DUCOM. Thewear on stainless steel (grade 304) is less compared to aluminumin all the three cases; varying time, angular rate and concentration.This is because of high yield strength of the Stainless Steel (grade304). The effect of particle hardness can be seen in Figs. 4 and 5.Alumina is harder than silica which will lead to cutting and defor-mation of the target material at higher rate than the silica particles.Hence, there is an increase in the volume loss of stainless steel(grade 304) and aluminum at all the above erosion parameters (dueto change in particle hardness and density),

Effect of corrosion:

vity Angular rate (rpm) Erosion time (h) Particle concentration (%)

Above 2000 At 1.5 Above 0.25Above 2250 At 1 and 2.5 Above 0.42

Above 2400 Above 1.5 Above 0.35– – –

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N.M. Dube et al. / W

Increase in angular rate, particle concentration and particleardness leads to removal of the passive layer at early stage and

ater the dissolution takes place. This is called as the transition of therosion dominated wear to corrosion dominated wear. The effectf corrosion on SS-304 in the alumina slurry is dominant above400 rpm, but negligible for the silica slurry at all angular rates,s shown in Fig. 7(b). In Fig. 8(b), above 45% particle concentra-ion there is a substantial effect of corrosion for the alumina slurrynd negligible compare to that for the silica slurry as shown. Theoft materials are more subjected to erosion–corrosion due to moreechanical wear. Change in the target material also has an effect

n the corrosion, as aluminum is more adhesive (oxide layer or theassivity layer on substrate) and soft (as such hardness is not a neces-ary criterion to predict erosion-corrosion) compared to the SS-304.he effect of corrosion at varying time portrays a negligible changen aluminum disc, which is not expected. The possible reason forhis has to be investigated.

All the above results are in a turbulent environment and needs aheoretical approach for verification. The assumption of corrosionctivity proportional to oxygen concentration has to be verified forurther confidence on this set-up.

. Conclusions

The development of a counter rotating double disc erosion testers reported here. This rig is compact, convenient to operate andet reliable for a first level erosion characterization of engineeringaterials on a routine basis. The test results using different con-

itions of slurry flow, erodent concentrations and exposure timendicated a systematic variation in the erosion wear consistent with

he behavior expected based on the known hardness propertiesf the test materials or the slurry mixtures used for experimenta-ion. For example, the erosion rate for alumina slurry is consistentlyigher than that for the case of silica slurry. Similarly higher erosionate is observed on aluminum discs as compared to that on stain-

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7 (2009) 259–263 263

less steel discs other test parameters being the same. At higher discrotation speeds, a turbulent environment is generated in the rig andthe results need to be further analyzed using a theoretical approach.The tests carried out in nitrogen environment indicated lower wearrate which could be due to reduced corrosion activity in oxygen freeenvironment as compared to ambient atmosphere. Further work isrequired for establishing such detailed aspects.

References

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[2] J.G.A. Bitter, A study of erosion phenomenon—parts I and II, Wear 6 (1963) 5–21,and 169-190.

[3] R. Girish, Desale, K. Bhupendra, S.C. Gandhi, Jain, Imporvement in the design ofa pot tester to simulate erosion wear due to viz solid–liquid mixture, Wear 259(2005) 196–202.

[4] H.M. Hawthrone, Y. Xie, S.K. Yick, A new Coriolis slurry erosion tester design forimproved slurry dynamics, Wear 255 (2003) 170–180.

[5] W. Tsai, J.A.C. Humphrey, I. Cornet, A.V. Levy, Experimental measurement ofaccelerated erosion in a slurry pot tester, Wear 68 (1981) 289–303.

[6] G.K. Batchelor, Note on a class of solutions of the Navier–Stokes equations rep-resenting steady rotationally-symmetric flow, Quarterly Journal of Mechanicaland Applied Mathematics 4 (1951) 20–41.

[7] K. Stewartson, On the flow between two rotating co-axial disks, in: Proceedingsof the Cambridge Philosophical Society, vol 49, 1953, pp. 333–341.

[8] B.J. Matkowsky, W.L. Siegmann, The flow between counter-rotating disks at highReynolds number, SIAM Journal on Applied Mathematics 30 (1976) 720–727.

[9] D. Eskin, Y. Leonnko, O. Vinogradov, On a turbulence model for slurry flow inpipelines, vol. 59, Chemical Engineering Science, 2004, pp. 557–565.

10] M.C. Roco, C.A. Shook, A model for turbulent slurry flow, Journal of Pipelines 4(1984) 3–13.

11] R. Gillies, C.A. Shook, Modelling high concentration settling slurry flows, TheCanadian Journal of Chemical Engineering 75 (2000) 709–716.

12] L.A. Oliveira, J. Pecheux, A.O. Restivo, On the flow between a rotating and acoaxial fixed disc: numerical validation of the radial similarity hypothesis, The-oretical Computational Fluid Dynamics 2 (1991) 211–221.

13] P. Novak, A. Macenauer, Erosion–corrosion of passive metals by solid particles,Corrosion Science 35 (1993) 635–640.

14] M.G. Fontana, Corrosion Engineering, IIIrd ed., Tata McGraw Hill, 2005.15] A. Neville, M. Reyes, H. Xu, Examining corrosion effects and corrosion/erosion

interactions on metallic materials in aqueous slurries, Tribology International35 (2002) 643–650.