Fabrication and Testing of Slurry Pot Erosion Tester
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- Gadhikar, A.A., Sharma, A., Goel, D.B. et al. Trans Indian Inst Met (2011) 64: 493. doi:10.1007/s12666-011-0075-8
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Slurry pot erosion tester is a simple and inexpensive test rig which can provide a rapid ranking of the erosion resistance for different materials. The fabrication of modified slurry pot erosion tester has been reported here. The present slurry pot erosion tester facilitates to handle large cylindrical and flat samples. It also allows using slurry with variety in its volume, and concentration and particle size of sand. The much needed uniform distribution of solid particles along the vertical section of the slurry is controlled by the speed of the stirrer. In the present investigation, the effect of stirrer speed on the distribution of sand particles inside the slurry pot is studied for variety of slurry. The optimum stirrer speed for uniform distribution of 300 μ sand particles over the vertical cross section in slurry of 10% concentration and 20 l volume comes out to be 850 rpm. The erosion behaviour of mild steel was also studied to ensure suitability of the device for determination of erosive wear.
KeywordsErosion test rigSlurry pot testerStirrer speedSolid distribution
In many industrial applications a surface is attacked by fluid stream containing solid particles which causes the erosive wear of the surface. It ultimately leads to repair or replacement of the component. Erosion is the most significant and continuing problem in many systems like catalytic cracking of oil, coal hydrogenation, fluidised bed system, transport lines for slurries, aeronautical, mining and process industries and thermal and hydroelectric power plants [1–4]. Use of better erosion resistant material can mitigate the deleterious effect of erosion in such applications. However, the accurate prediction of erosion behaviour of material is very difficult as numerous parameters govern the erosion phenomenon. All these parameters can be broadly classified as (i) impinging variables, (ii) particle variables and (iii) material variables . The relative importance of these parameters in the systems undergoing erosive wear varies depending on the different flow configurations and their physical characteristics. Generally laboratory test method is popularly adopted  to evaluate erosion resistance of material in which practical conditions are simulated to generate meaningful and reproducible data. In practice, generally erosive wear takes place at low rates. Hence the simulation test period becomes lengthy. In such circumstances, widely accelerated erosion conditions may be imposed with precision to shorten the test period.
Literature Review on Methodology and Design of Erosion Testers
The standardization of methodology and design of equipment for erosion testing is difficult to achieve considering the complexity of the problem. Clark  opined that no ideal erosion test was likely to exist which would allow the prediction of erosion rate and its distribution in any flow regime under any material or slurry condition along with optimization of hardware design criteria. Subsequently no universal correlation valid for all types of slurries could be obtained to determine wear rate in a slurry pipe line . However, at a lower level of expectations, many lab tests can be used for performance ranking of the materials and study of influencing factors. Various types of erosion test rigs used so far for determination of erosion rate in different conditions can be listed as linear gas gun , slurry pot erosion tester [10, 11], contra rotating disc tester , slurry jet erosion wear test rig , sliding bed erosion test fixture , flow-through slurry wear tester  and sliding bed wear test and closed hydraulic loop tester . Those can be further classified into four types  as sand or gas-blast rig , re-circulating liquid slurry loop , centrifugal accelerator and whirling arm rig [19, 20]. The most commonly used bench scale test rigs to evaluate the erosive wear at an accelerated rate are slurry pot tester (a variant of whirling arm rig) and jet impingement tester (JIT) (sand blast type). Slurry pot tester can provide a rapid ranking of the erosion resistance of different materials besides being inexpensive and easy to operate . However the investigation on the effect of particle size, impact velocity and impact angle cannot be undertaken with slurry pot tester . JIT is generally applied to determine the variation of the wear with impact angle at low solid concentration. However, the impact angle and the impact velocity of all the solid particles do not remain same during the test in JIT [23–25]. The inadequate grasp and control of particle impact conditions in the test rig ultimately leads to erroneous data on erosion behavior of material . Efforts are being taken for the continuous modification in the design of existing test rigs to overcome the flaws/limitations observed in them [27, 28]. Recently, the coriolis tester (a variant of centrifugal accelerator), has been reported to be simple and rapid with excellent control of experimental condition . There, coriolis effect is used to closely simulate the action of slurries moving inside centrifugal pump, cyclones etc. . However, the above discussed test rigs mostly operate under laminar flow conditions. In order to study the erosion due to turbulence, a compact, convenient and reliable counter rotating double disc tester has been reported for first level erosion characterization of engineering materials .
However, the slurry pot tester is reported to give comparatively more realistic results for many field applications and hence it is preferred over other tester which can be prohibitively expensive and time consuming [6, 8, 10]. In the present work, a slurry pot tester is fabricated, keeping in view all the problems faced earlier, to evaluate the erosion resistance of variety of material for various erosion parameters. The effect of stirrer speed on solid distribution in variety of slurry is also studied. Experiment on erosion of mild steel in sand-water mixture has been carried out to ensure suitability of the device for determination of erosive wear.
Fabrication of Slurry Pot Tester
The tank is covered by a transparent acrylic sheet from the top which allows to view the inside portion of the tank during testing. Another 0.75 KW DC motor is directly mounted on the top of the acrylic sheet. As shown in Fig. 1a, the stainless steel shaft attached to the motor is inserted from the acrylic lid to hold and rotate the wear specimen inside the slurry at required speed as can be measured by non contact type digital tachometer. The wear samples can be in the form of either right circular cylinder of 10 mm diameter or rectangular plate of 20 × 3 mm2 cross section with a T-Shaped head at the top. These samples, maximum four in number, can be fitted in the matching groove on the sample holding disc. The holding disc is then bolted to supporting disc attached to holding shaft and the whole assembly is then fitted to the motor shaft. The degree of freedom for wear specimen is designed to be zero to avoid relative motion during test (Fig. 1c). All the components of the holding fixture are made up of stainless steel.
It was thought that the quantification of the impact angle in the pot tester was difficult due to complex relative flow conditions between the slurry and the wear specimen during the test . However, the orientation angle of the specimens was varied to study the effect of impact angle . The orientation angle was defined as the angle between tangents to the plane surface and its velocity. Special test fixture was designed for analyzing the effect of impact angle in the slurry pot tester . The flat wear sample in the present pot tester can also be placed at different orientation angle as shown in Fig. 1d by selecting the holding disc with grooves in the desired orientation angle.
The acrylic lid along with the motor and the special holding assembly can be lifted up through rope winch system for loading and unloading of sample. The guiding rods help easy placing of the lid on the tank. The lid can be bolted to the tank flanges at the top. The tank is provided with total five outlets at different height along the wall. The outlet at the bottom (D) is solely for draining the tank whenever the used slurry has to be replaced by new slurry. The remaining four ports (T1, T2, T3, T4) are arranged at 75, 150, 225 and 300 mm from bottom and alternately at left and right side of the drain port. These ports are used to check the actual sand concentration at different height from the bottom.
Optimization of Stirrer Speed
Parameters for optimisation of stirrer speed
Type and sp. gravity of sand
Overall sand concentration
5, 10, 20% (in 20 l water)
Avg. sand particle size
300 μm (150–450 μm), 525 μm (450–600 μm), 750 μm (600–900 μm)
750, 850, 950 rpm
Tap position from bottom
T1: 75 mm, T2: 150 mm, T3: 225 mm
Testing of Mild Steel for Erosion Resistance
Parameters for erosion testing of mild steel
10 mm dia., 45 mm height
Avg. sand particle size
Sample rotation speed
Overall sand concentration
Sp. gravity of sand
Result and Discussion
The present slurry pot erosion tester facilitates to handle larger samples and variety of slurry and its volume. Also, the orientation angle of the specimen and the speed of the sample rotation can be conveniently adjusted to suit the experimental requirements. The distribution pattern for the given slurry can be checked at any time by measuring the relative concentration at the vertical section of the slurry. Accordingly stirrer speed can be adjusted.
Effect of Stirrer Speed
Effect of Slurry Concentration
Effect of Particle Size
Erosion Behaviour of Mild Steel
The modified slurry pot erosion tester has the capacity to handle large samples and variety of slurry. The arrangement of adjustable specimen orientation angle and stirrer speed facilitate for erosion testing of material under different conditions. The precise control over the suspension characteristics of the slurry ensures the accurate and reproducible data of erosion behavior of materials.
From the experimental study it is observed that the rise in stirrer speed improves the uniformity of the flow along the vertical section. The increase in overall sand concentration of the slurry requires more energy for suspension of additional sand particles. Hence stirrer speed needs to be increased to maintain the uniformity of the flow.
The increase in the size of sand particles tends to reduce the effect of liquid drag on the bigger particle. Hence these particles do not closely confirm with the flow of liquid medium. This also calls for increase in stirrer speed to improve the distribution pattern of the sand particles in the slurry.
Thus the optimum stirrer speed is different for variety of slurry and it mainly depends on the concentration and size of sand particles in the given volume of the slurry. The optimum stirrer speed was found to 850 rpm most uniform distribution of 300 μ sand particles over the vertical cross section of the slurry of 10% concentration in 20 l volume.
For slurries of higher overall concentration and sand particle size, the uniform distribution of the sand particles along vertical section of the pot tester can be obtained at higher stirrer speed. However the excessive increase in the stirrer speed will cause turbulence and formation of vortices in the slurry pot. Hence stirrer speed needs to be controlled in the constraint of turbulent flow conditions to obtain more uniformity in the distribution of sand particles.
The results obtained from the erosion testing of mild steel in the present slurry pot tester are found to be consistent with the literature. This ensures realistic results for the various erosion conditions in pipeline, pump, water turbines etc.