Silt Erosion Research Articles

Investigation on laser hardened and WC-Co-Cr based HVOF coated 13Cr 4Ni martensitic stainless steel materials under erosive environment

Abstract Coating materials are used on turbine blades. Coating plays an important role to protect the turbine blades from the silt erosion. In this study, comparison for erosion resistance between uncoated specimens of 13Cr 4Ni martensitic stainless, WC-Co-Cr based HVOF coated and laser hardened 13Cr 4Ni martensitic stainless steel specimens was carried out by performing air jet erosion tests. The micro structural analysis of eroded samples was done to ascertain the mode of erosion. From investigations it was observed that WC-Co-Cr based HVOF coated 13Cr 4Ni martensitic stainless steel specimens displayed maximum erosion resistance at all impingement angles i.e. 30°, 45° and 90° in comparison to uncoated and Laser hardened 13Cr 4Ni martensitic stainless steel specimens. Mass loss of WC-Co-Cr based HVOF coated 13Cr 4Ni martensitic stainless steel specimens were 0.0075, 0.007 and 0.005 g at 30°, 45° and 90°, respectively. Taguchi based design of experiment is implemented for optimizing the input process parameters. The calculated value of the whole mean of signal to noise (S/N) ratio for erosion wear is −89.2554 db for Bare material, −127.9290 db for HVOF coted material and −109.4730 db for laser hardened material observed. According to findings surface treatment of testing samples significantly affect erosion resistance.

Application of machine learning for hydropower plant silt data analysis

Among all renewable energy resources, hydropower is the most predictable and reliable source of energy. In the Himalayan region, most of the hydropower plants suffer from the problem of silt erosion. During the monsoon period, the quantum of silt particles is remained quite high, which damages the hydro-mechanical components of the plant. In order to reduce the risk that occurred by the silt erosion, a popular machine learning-based technique can be used. The Self-Organizing Map (SOM) algorithm based on artificial neural networks offers a broad range of techniques for the visualization of data. Under the present paper, a novel technique is used on MB-II (304 MW) hydropower plant of UJVN Ltd., which will classify the density of silt data resulting from neighbor and radius based distances. Based on the analysis of the silt data, maintenance scheduling of hydropower plants can be planned. The SOM technique provides a better insight into silt data. It identifies outliers data as well as useful data that can be used for accurate prediction of daily silt pattern.

Experimental Research on Filtration Effect of Mesh Filters in Dewatering of Silt Foundation

The filtration effect of four different filter structures is studied. These four designed filters are used in three different dry densities silt sand. The four filters are: 1) without filter; 2) 80 mesh single-layer filter structure; 3) 120 mesh single-layer filter structure; 4) one 80 mesh and one layer of 120 mesh filter combination structure. The result shows that the permeability coefficient of the soil is affected by the mesh size. The smaller the pore size, the lower permeability in the soil. The effect of filter depends on the aperture. The aperture of the filter influences the quality of sand adhere to the filter, and affects the silt erosion. The result of the experiment provides a suggestion for the selection of the mesh filters in the precipitation of the two-dimensional foundation.

Selection of Erosive Wear Rate Parameters of Pelton Turbine Buckets using PSI and TOPSIS Techniques

Hydro turbine machineries erosion due to silt is a complex issue for the effective practice of hydropower plants. Erosion caused by silt of the Pelton turbine buckets is a compound phenomenon that depends on size of silt particles , silt particles concentration , velocity of jet , and working time . This paper deals with the influence of silt erosion for various silt loaded factors and effective parameters. The preference selection index (PSI) and technique for order of preference by similarity to ideal solution (TOPSIS) approaches has been adopted to find optimal set of parameters which offers the highest performance for the Pelton turbine. Based up on the results obtained from both PSI and TOPSIS approaches it is found that optimal performance has been provided by A-1 alternate with geometric and flow parameters as , , and respectively.

Identification of Silt Erosion Areas on Francis Turbine Guide Vanes Through Numerical Simulation

Hydro power plants in Himalayan region are severely affected by silt erosion and cavitation, and their combined effect, as both of these factors complement each other. The problem of silt erosion is acutely felt during monsoon season of the year, as silt laden water with high silt concentration, enters the turbine. Many researchers have reported the reduction in turbine hydraulic efficiency due to silt erosion in guides and runner vanes. In addition, the erosion in the blades also increases the maintenance cost and downtime period. The present work includes a numerical simulation to investigate the sediment erosion on guide vane. The numerical simulation has been carried out on Fluent software. The k-ω turbulent model has been applied to a 3-D model of NACA4412 blade profile. The simulations have been performed at an angle of attack equal to 20o for the range of water velocity 5–20 m/s and for silt concentration varying from 1000 to 4000 ppm. In all the cases considered in this study, the results shows a significant erosion at the leading edge followed by sparse erosion on the bottom side of the guide vane. The study will act as a precursor for experimental studies in the future. Accurate identification of erosion regions in turbines will help mitigate the problem easily.

Alternative Design of Double-Suction Centrifugal Pump to Reduce the Effects of Silt Erosion

Large amounts of sediment in the Himalayan rivers causes severe silt erosion to the hydraulic machinery operating along these rivers. In this study, the effects of silt characteristics on the silt-erosion characteristics of a double-suction centrifugal pump was studied and the anti-erosion property of bionic convex domes on silt erosion under these conditions was explored by using computational-fluid-dynamics methods, partly supported by a painted-blade erosion experiment. The results show that the silt size affects the erosion position and erosion strength, whereas the silt concentration mainly affects the erosion strength for the studied range. The bionic convex domes provide an effective solution to improve the silt erosion for most of the investigated silt-laden conditions by decreasing the erosion rate and the erosion area of the blade. The anti-erosion mechanism was studied combined with large eddy simulation. The analysis shows that the relative velocity of water around the blade surface is changed and the mass flow rate of silt particles hitting the blade is reduced by inducing swirling flows around the bionic convex domes.

Cavitation–silt erosion in sand suspensions

Cavitation–silt erosion in sand suspensions has elicited research attention. However, erosion characteristics in various conditions of liquids remain unknown due to their complex mechanisms. Thus, the effects of sand size, concentration, and temperature of sand suspensions on cavitation–silt erosion and viscosity were experimentally investigated in the present work. The findings proved the existence of critical sand size. The silt–cavitation erosion decreased with the increase of sand concentration when the sand was smaller than the critical size, and it increased with the increment of the sand size and temperature. A good relationship between the viscosity and the sand size, concentration, and temperature was determined. Moreover, the cavitation–silt erosion mechanisms were obtained on the basis of the viscosity and impingement erosion analysis standpoint.

Improved Resistance of Nanoparticle-Laden Polymer Coatings Subjected to Combined Silt and Cavitation

Abstract Hydropower generation, particularly in the Himalayan region during monsoons, suffers because of the erosion of turbine components, which is due to the high concentration of silt present in water. These high-power machines also suffer from cavitation, especially at off-design conditions. However, erosion caused by the synergistic effects of silt and cavitation can cause more serious degradation, is more complex, and remains an unsolved problem in hydraulic machines. The present work addresses this concern through the systematic study of different polymeric coatings under a controlled silt and cavitation environment. This article discusses the design and development of an experimental facility, where a specimen can be subjected to combined submerged slurry jet along with acoustic cavitation produced by a focused ultrasonic transducer. Novel polymeric coatings made of polyurethane (PU) reinforced with hard nanoparticles (B4C and SiC) of varying concentrations (from 1 to 75 weight percentage [wt. %] being defined with respect to polymer weight) are used in this work. These coatings show erosion resistance superior to the base material (16Cr-5Ni martensitic stainless steel) commonly used to make hydroturbine blades. Results are divided into three divisions. At first, we present erosion kinetics and discuss possible erosion wear mechanisms based on pure silt erosion experiments. Afterwards, pure cavitation erosion and synergistic studies of silt and cavitation studies under different experimental conditions are presented. Base material showed the maximum mass loss rate of ∼22 mg/h, pure PU suffered ∼9 mg/h, while nanoparticle-reinforced PU (10 wt. % B4C or 2 wt. % SiC) has a loss of ∼1.5 mg/h. This shows the tremendous potential that this approach of using polymer laden with hard nanoparticles has in combating the synergetic effects of silt and erosion. The results are well-supported by detailed scanning electron microscope images and analyses to explain the reason behind the successful performance of the coatings.

Studies on Enhancement of Silt Erosion Resistance of 13/4 Martensitic Stainless Steel by Low-Temperature Salt Bath Nitriding

Low-temperature salt bath nitriding of heat treated and tempered 13/4 Martensitic stainless steel (13/4HTT) was carried at 450 °C (N450) and 500 °C (N500) for 10 h each. The nitrided samples were characterized by using x-ray diffractometer, field emission scanning electron microscope and optical microscope. The nanohardness and elastic modulus of the cross section of nitrided specimen were measured by nanoindentation test using Hysitron TI950 triboindenter. The nitrided 13/4HTT (N450 and N500) and 13/4HTT specimens were subjected to slurry erosion test in a slurry pot tester. The test was conducted for 48 h, and weight loss was measured after every 6 h. The relative speed of slurry with respect to specimen was 4.55 m/s. It was found that the weight loss due to erosion of the N450 is 83% less than that of 13/4HTT and that of N500 was 92% more than that of 13/4HTT. The erosion mechanism is correlated to the phases present in the specimens. The improvement in the slurry erosion resistance of N450 is due to presence of expanded martensite ( $$\alpha_{N}$$ -Fe). Increasing the temperature of nitriding to 500 °C led to the decrease in the slurry erosion resistance of N500 due to the formation of brittle CrN phase.

Advanced condition monitoring of Pelton turbines

The ability of hydropower to adapt the electricity generation to the demand is necessary to integrate wind and solar energy into the electrical grid. Nowadays, hydropower turbines are required to work under harsher operating conditions and an advanced condition monitoring to detect damage is crucial.In this paper the methodology to improve the condition monitoring of Pelton turbines is presented. First, the field data obtained from the vibration monitoring of 28 different Pelton turbines over 25 years has been studied. The main types of damage found were due to fatigue, cavitation and silt erosion. By analyzing the vibration signatures before and after maintenance tasks, the symptoms of damage detected from the measuring locations were determined for each case.Second, a theoretical model using numerical methods (FEM) was created in order to simulate the dynamic behavior of the turbine. The model was validated with the results obtained from on-site tests that were carried out in an existing turbine. The deformations and the stresses of the runner under different operating conditions could then be computed.The calibrated model was used to analyze in detail the effect of misalignment between nozzle and runner. In historic cases, this abnormal operating condition lead to severe damage in the turbine, due to the effect of fatigue in some locations of the buckets. The model reproduced well the symptoms detected in the field measurements. The stresses could be calculated, which eventually can be used to estimate the remaining useful life of the turbine.

Influences of sand cover on erosion processes of loess slopes based on rainfall simulation experiments

Aeolian-fluvial interplay erosion regions are subject to intense soil erosion and are of particular concern in loess areas of northwestern China. Understanding the composition, distribution, and transport processes of eroded sediments in these regions is of considerable scientific significance for controlling soil erosion. In this study, based on laboratory rainfall simulation experiments, we analyzed rainfall-induced erosion processes on sand-covered loess slopes (SS) with different sand cover patterns (including length and thickness) and uncovered loess slopes (LS) to investigate the influences of sand cover on erosion processes of loess slopes in case regions of aeolian-fluvial erosion. The grain-size curves of eroded sediments were fitted using the Weibull function. Compositions of eroded sediments under different sand cover patterns and rainfall intensities were analyzed to explore sediment transport modes of SS. The influences of sand cover amount and pattern on erosion processes of loess slopes were also discussed. The results show that sand cover on loess slopes influences the proportion of loess erosion and that the compositions of eroded sediments vary between SS and LS. Sand cover on loess slopes transforms silt erosion into sand erosion by reducing splash erosion and changing the rainfall-induced erosion processes. The percentage of eroded sand from SS in the early stage of runoff and sediment generation is always higher than that in the late stage. Sand cover on loess slopes aggravates loess erosion, not only by adding sand as additional eroded sediments but also by increasing the amount of eroded loess, compared with the loess slopes without sand cover. The influence of sand cover pattern on runoff yield and the amount of eroded sediments is larger than that of sand cover amount. Furthermore, given the same sand cover pattern, a thicker sand cover could increase sand erosion while a thinner sand cover could aggravate loess erosion. This difference explains the existence of intense erosion on slopes that are thinly covered with sand in regions where aeolian erosion and fluvial erosion interact.

Silt Erosion in Hydro Turbines and Status of Small Hydropower in India - A Review

Silt Erosion in Hydro Turbines and Status of Small Hydropower in India - A Review

Slurry Erosion Behaviour of Pack Boronized 13-4 Martensitic Stainless Steel for Hydro Turbine Blades

Pack boronizing of hydro turbine blade steel i.e. 13Cr-4Ni martensitic stainless steel (13-4 MSS) has been conducted as a protective coating against silt erosion. A boride coating of approximately 40 µm was deposited on the samples. Slurry pot method was used to evaluate the erosive wear resistance in which samples were rotated in an abrasive slurry of 100 g/litre silica sand (size 210 – 297 µm) in water at a speed of 4.45 m/s for a period of 40 hrs. Higher wear resistance of pack boronized 13-4 MSS has been attributed to the higher hardness of boride coating (2300 VHN) over that of bare 13-4 MSS (345 VHN).

Stainless Steels as Erosion Resistant Materials for Hydraulic Machines

The corrosion phenomena lead to serious modifications in the structure of metallic materials from which are manufactured the important active components of hydraulic machines. There are two important types of corrosion: cavitation and silt erosion (abrasive erosion), that are specific to machines which are producing energy [1, 2, 3]. As a corrosion mechanism, in hydrodynamic cavitation [4, 5], when cavitation bubbles implode on the solid surface of hydraulic machine component, the local pressure developed is high and can exceed the fatigue strength, yield point or compression strength of the material. Cavitation phenomenon can be produced in different ways. Four types of cavitation are described in the literature, looking for the method of producing, [6]: hydrodynamic cavitation, particle cavitation, acoustic cavitation, and optic cavitation. Abrasive erosion is the gradual degradation of a structure under the action of solid particles suspended in the working fluid. Impact and sliding erosion are the main categories of abrasive erosion approached in the literature by considering the mechanisms of which the abrasive particles act on the metallic surface, [2]. In the last decades the abrasive erosion phenomenon became a serious problem for the efficient operation of power plants, for instance in hydropower plants [7, 8]. Geothermal energy is the heat energy of the earth given by capturing the springs of heat water. In Romania the geothermal energy is used only for heating because the water has a low temperature and cannot be used to produce electric energy, only heat energy. So, although Romania is the third highest potential geothermal in Europe, practically electric energy from geothermal resource has a low thermal potential, [9]. A steam turbine is working at high rotational speed, high temperatures and using the working fluid which could be steam or wet steam. The working fluid is composed of corrosive chemicals with an aggressive pH. For this reason the common problems of the geothermal steam turbine failures are given by fractures of the blades (rotor blades or stator blades).

A pragmatic approach and quantitative assessment of silt erosion characteristics of HVOF and HVAF processed WC-CoCr coatings and 16Cr5Ni steel for hydro turbine applications

In the present study, WC-CoCr hard composite coatings were deposited on the hydro turbine steels using two different thermal spray techniques such as High Velocity Air Fuel (HVAF) and High Velocity Oxy Fuel (HVOF). The slurry erosion tests were performed with three different jet impingement kinetic energies and at five different impact angles. The influence of impact angle on the erosion wear behavior of the coatings was analyzed using CFD simulation technique. Erosion mechanisms were investigated in detail using SEM and laser scanning confocal microscopy. Among all the WC–CoCr coated samples, the HVAF coating sprayed at highest spray velocity has shown superior erosion resistance compared to the HVOF coatings. It could be attributed to the better adhesion, higher density, enhanced hardness and surface compressive residual stresses coupled with lower oxidation of the coated samples. The erosion wear mechanisms were found to be nearly micro-cutting and plowing with layered material removal at a lower impact angle and a low cycle fatigue linked to repeated impact leading to rounding of the edges and brittle cracking of the WC grains at normal impact conditions.

Structural Aspects of Silt Erosion Resistant Materials Used in Hydraulic Machines Manufacturing

The corrosion effects caused by cavitation and silt erosion (abrasive erosion) phenomena lead to serious modifications in the structure of metallic materials from which are manufactured the important active components of hydraulic machines. In the first part of the paper, a brief presentation of the mechanism of silt erosion phenomenon comparatively with the cavitation one is made. The synergy between cavitation-erosion-corrosion is approached. The structure elements of the most used metallic materials corrosive resistant are described, too. It follows a comparative synthesis of specific structures stainless steels resistant to cavitation erosion and abrasive erosion. The structures of new stainless materials, originally obtained in the laboratory, are discussed on Schaeffler's diagram showing the influence of alloying elements on these forms of corrosion.

Quantification of Metal Loss Due to Silt Erosion under Laboratory Conditions

Quantification of Metal Loss Due to Silt Erosion under Laboratory Conditions

Field application of a multi-frequency acoustic instrument to monitor sediment for silt erosion study in Pelton turbine in Himalayan region, India

High sediment load passing through hydropower components erodes the hydraulic components resulting in loss of efficiency, interruptions in power production and downtime for repair/maintenance, especially in Himalayan regions. The size and concentration of sediment play a major role in silt erosion. The traditional process of collecting samples manually to analyse in laboratory cannot suffice the need of monitoring temporal variation in sediment properties. In this study, a multi-frequency acoustic instrument was applied at desilting chamber to monitor sediment size and concentration entering the turbine. The sediment size and concentration entering the turbine were also measured with manual samples collected twice daily. The samples collected manually were analysed in laboratory with a laser diffraction instrument for size and concentration apart from analysis by drying and filtering methods for concentration. A conductivity probe was used to calculate total dissolved solids, which was further used in results from drying method to calculate suspended solid content of the samples. The acoustic instrument was found to provide sediment concentration values similar to drying and filtering methods. However, no good match was found between mean grain size from the acoustic method with the current status of development and laser diffraction method in the first field application presented here. The future versions of the software and significant sensitivity improvements of the ultrasonic transducers are expected to increase the accuracy in the obtained results. As the instrument is able to capture the concentration and in the future most likely more accurate mean grain size of the suspended sediments, its application for monitoring silt erosion in hydropower plant shall be highly useful.

Silt erosion study on the performance of an impulse turbine in small hydropower

Silt particle laden flow through hydro turbine components causes erosion to the surface which comes in contact with it. Silt size, silt concentration, velocity of flow, properties of silt materials and operating hours of turbine play a vital role in damaging the turbine components. Efficiency of the turbine decreases with increase in erosive wear. The present study has been carried out to experimentally investigate the effect of silt size, silt concentration, jet velocity and operating time on performance of Turgo impulse turbine under actual flow conditions. It has been found that turbine efficiency loss strongly depends upon silt parameters. Existing test bed has shown erosion wear up to 1.8%, therefore resulting in the loss of power generation. Based on experimental data obtained for different parameters, correlations have been developed for the prediction of percentage efficiency loss of Turgo impulse turbine.

Erosion Characteristics of Nanoparticle-Reinforced Polyurethane Coatings on Stainless Steel Substrate

Hydropower generation from the Himalayan rivers in India faces challenge in the form of silt-laden water which can erode the turbine blades and reduce turbine life. To address this issue, polyurethane coatings reinforced with boron carbide (B4C) or silicon carbide (SiC) nanoparticles on 16Cr-5Ni martensitic stainless steel substrate were used in the present investigation to improve erosion wear resistance in silt erosion conditions. Slurry erosive wear tests were carried out based on ASTM G-73 protocol at various test conditions of impact velocity, impingement angle, and erodent particle size as well as slurry concentrations as determined by the implementation of Taguchi design of experiments. Analysis of variance studies of erosion rate indicated that nanoparticle content in PU material is the single most important parameter, and interaction of impact velocity and impingement angle was also proved to be significant. The coatings with B4C nanoparticles had higher wear resistances than those with SiC nanoparticles due to higher hardness of the former. An interesting finding from the results is that there is an optimum amount of nanoparticles at which mass removal is the minimum. This observation has been explained in terms of surface characteristics of coatings as brought out by a combination of measurements including SEM images as well as roughness measurement.