Assessment of the erosion resistance of steels used for slurry handling and transport in mineral processing applications

The wear environment of steels used for containing, transporting and processing erosive mineral slurries is often such that fluid borne particles form a layer moving at high speed across the wearing surface. Information on the performance ranking of such materials is limited, particularly with respect to the influence of steel hardness and microstructure on the resistance to erosion. This is particularly important for the oil sands industry of Northern Alberta where handling and processing of essentially silica-based solids results in extremely severe wear conditions. This paper presents slurry erosion data obtained on 11 commercially available wear resistant plate and pipeline steels with hardness values up to 750 HV. These data were obtained using a Coriolis erosion tester operated at 5000 rpm with an aqueous slurry containing 10 wt.% of 200–300 μm silica sand particles.

The Coriolis erosion tester was selected because it provides a low-angle scouring action that simulates the erosive conditions encountered in oil sands and tailings pipeline transport and in some related processing operations. Results show that this test method is able to discriminate clearly between the erosion resistance of these steels, expressed in terms of specific energy (the energy necessary to remove unit volume of test material), with the most erosion resistant steel being more than five times superior to the least resistant. A graphical relation between steel hardness and erosion resistance is given. A comparison is also made between slurry erosion data and the performance of the materials in the ASTM G65 dry sand rubber wheel (DSRW) sliding abrasion test. Comments on the influence of the macro- and microstructures of the steels on their wear behaviour are included.     

Electrochemical investigation of erosion-corrosion using a slurry pot erosion tester

The aim of this paper is to use a modified slurry pot erosion tester to perform in-situ electrochemical measurements during solid particle impingement to investigate the effects of velocity, sand size and sand concentration on a passive metal (UNS S31603). Samples are subjected to a set of erosion-corrosion experiments. The electrochemical response of UNS S31603 to the test parameters is plotted and compared to develop an understanding of the erosion-corrosion process. The current trend with variation of test parameters has been explained by an erosion enhanced corrosion synergistic effect. The current transients associated with depassivation and repassivation during solid particle impingement are observed through electrochemical noise measurements. It was observed that the increase in velocity and sand concentration increased the current levels during erosion-corrosion. However, the increase in sand size had a more complex response. Single particle impact experiments conducted revealed that the peak corrosion current and the repassivation time increased with increase in velocity. A linear trend was seen between the peak current and the kinetic energy. A second-order exponential decay was fitted to the repassivation kinetics of the single particle impact. SEM has been used to develop a mechanistic understanding of erosion-corrosion. The surface scars reveal that the depth of the craters and the length of the lips increase with increase in velocity. Micro-cracks also appear on these lips, believed to be due to corrosive action attacking the roots of these lips.     

Scouring erosion resistance of metallic materials used in slurry pump service

Low impact angle erosion resistance is a critical requirement of materials used in pumps, piping, valves, nozzles, cyclones and other components which transport and process most mineral slurries.The Coriolis method offers a suitable technique for assessing behavior under such scouring attack conditions. It is being used increasingly in support of the mining/mineral processing industry, to compare and discriminate between candidate materials and also assist in the development of new products and protection systems. The specific method used in the current study involves high velocity erosion with aqueous slurry containing 10 wt.% of AFS 50-70 silica test sand. This compares reasonably with the main, extremely abrasive solids constituent encountered in mining and processing oil sands deposits in northern Alberta, Canada. These are becoming a rapidly growing and critically important source of oil in North America.Abrasion resistant chrome white iron castings typically covered by the ASTM A532 standard, are used widely in slurry pump components particularly in oil sand operations. However, the development of proprietary cast hypereutectic chromium white irons with microstructures containing primary M₇C₃-type carbides, is providing the capability to significantly improve the wear performance of such parts. In certain applications where corrosion contributes significantly to overall attack, lower carbon and higher chromium-bearing variants are employed.A comparison of the Coriolis erosion behavior of a wide range of commercially available cast wear and corrosion resistant and high toughness alloys used in pump manufacture, has confirmed anticipated performance ranking and the superiority of the latest generation of hypereutectic chrome white irons. The ameliorative influence on scouring erosion behavior of high carbon content, hardness and carbide volume fraction and particularly of fine carbide size has been demonstrated. A correlation is drawn between test data and service performance.     

Effect of test parameters on large particle high speed slurry erosion testing

Abstract

A high speed slurry-pot wear tester was developed for close-to-reality heavy-duty wear testing of materials used in mineral applications. The samples are attached on four levels in a pin mill configuration. The tester and the developed sample rotation test method deliver reproducible results. This study focuses on the effects of testing parameters in large particle slurry testing. Parameters such as the speed, particle size and slurry concentration were varied. The effect of test duration was also examined. Round steel samples and slurry of water and granite gravel were used for testing. The test parameter variations were 4 to 10 mm for particle size, up to 23 wt-% for concentration and up to 20 m s^?1 for the sample tip speed. The relationships between the parameters are discussed. The kinetic energy of the large abrasive particles is also considered. Wear surfaces studied with optical and electron microscopy are also presented and discussed.     

Sand–water slurry erosion of API 5L X65 pipe steel as quenched from intercritical temperature

The objective of this study was to analyse the erosion of API 5L X65 pipe steel whose microstructure consisted of ferrite and martensite obtained by quenching from intercritical temperature (770°C). Jet impingement tests with sand–water slurry were used. The changes in mechanical properties, caused by heat treatment carried out, did not induce changes in either the mechanism or erosion resistance. The erosion rate increased with angle of attack until 30° and later decreased until 90°. The microtexture of the eroded surfaces, at angles of attack of 30° and 90°, were similar for both conditions and were composed of craters and platelets at several stages of evolution. The erosion mechanism was by extrusion with the forming and forging of platelets.     

Evaluation of a semi-empirical model in predicting erosion–corrosion

The phenomenon of erosion–corrosion has been studied extensively by various investigators but no accurate model has been developed to predict the interactions between erosion and corrosion. This is mainly attributed to the complexity of the interactions that generate either a synergistic or antagonistic wear effect for a particular material in a certain environment. A semi-empirical model has recently been developed at the University of Southampton which incorporates dynamic Hertzian contact mechanics to model the damage during particle impact and accommodates the effect of erodent deforming the surface leading to an increased corrosion activity. The model was found to have good agreement with erosion–corrosion rates of carbon steel. The aim of this paper is to evaluate the robustness of this semi-empirical model by testing it on a passive metal. UNS S31603 was chosen due to its inherent passivity to corrosion. A slurry pot erosion tester was used as the test rig to perform the experiments. It was found that this passive metal produces high synergistic levels when exposed to erosion–corrosion in 0.3 M HCl with variation in erodent concentrations and flow velocities. SEM and surface profilometry show typical ductile material behaviour with cutting mechanism and deformation mechanism occurring simultaneously. A wear map is presented and it is observed that the increase in velocity and sand concentration causes the material to shift from a corrosion–erosion dominated region to an erosion–corrosion dominated region. This paper will also evaluate the semi-empirical model and discuss its applicability in predicting erosion–corrosion.     

Degradation process of typical Ti(C,N)–Mo2C–Ni cermet in slurry erosion conditions

Degradation process of Ti(C,N)-based cermet is investigated in solid–liquid erosion conditions. The results indicate that the erosion process of Ti(C,N)-based cermet is classified into incubation, development and prevalence. In the incubation stage, the weight loss is dominated by binder deterioration; in the development stage, ceramic phase and binder failure contribute to the material loss; and in the prevalence stage, ceramic fragments removal is responsible for the material loss. Impingement of Al₂O₃ particle results in ceramic phase deterioration, while in binder the degradation is caused by impingement and microcutting. Microcracks nucleate firstly at the interface and/or in the rim phase.     

Evaluation of erosive wear resistance of TiN coatings by a slurry jet impact test

In this paper, it is proposed to use a new type of solid particle impact test (slurry jet) to swiftly evaluate wear properties of thin, single layered or multilayered coatings. By the slurry jet, 1.2 μm alumina particles were impacted at high velocity perpendicular to thin PVD coatings of TiN deposited on high speed steel substrate materials under various substrate temperatures. Since the coatings have a much higher wear resistance than the substrate material, the wear rate increases significantly to the higher level of the HSS material when the coatings are penetrated. This is utilized in the quantification of the assessment of coating wear. A ranking of wear resistance and correlations to the coating surface hardness measured by nano-indentation tests, and coating morphology and structures are given and discussed. The TiN deposited under the highest substrate temperature proved to have the highest wear resistance although it had a relatively low hardness. The wear rate of the TiN coatings varies with the orientation of grains, that is, the {1 1 1} orientation that dominates for the high temperature deposition shows a higher wear resistance than the {1 0 0} orientation, which corresponds with the cleavage fracture behavior. Thus, it can be recommended as a screening test when evaluating coatings and coated materials.     

Effect of heat treatment on the structure,cavitation erosion and erosion–corrosion behavior of Fe-based amorphous coatings

In this study, high-velocity oxygen-fuel sprayed amorphous coatings have been heat treated at various temperatures to form microstructures with crystalline phases. The structure, micro-hardness, cavitation erosion resistance and erosion–corrosion resistance of these coatings are compared. Crystalline phases are discovered in the coatings after heat treatments at 650 °C and 750 °C. The coating heat treated at 750 °C exhibits the poorest cavitation erosion resistance in 3.5 wt% NaCl solution among all coatings due to the degraded corrosion resistance. However, the hardness of the crystallized coating can reach 1000 Hv and the erosion–corrosion resistance of the heat treated coating is better than the untreated one.     

Investigation of erosion-corrosion mechanisms of UNS S31603 using FIB and TEM

Accelerated wear due to synergy during erosion-corrosion of UNS S31603 is extremely complex. It is this reason that current modelling approaches fail to accurately model the physical mechanisms in this wear process. The objective of this work was to perform FIB and TEM analysis on UNS S31603 to investigate the subsurface deformation mechanisms and microstructural changes in the material during erosion-corrosion. FIB investigation revealed a decrease in grain size at the surface and a change in grain orientation towards the impact direction. Networks of cracks were observed near the surface which is believed to be caused by work hardening of the material which increased the material susceptibility to fatigue cracking. Folding of lips is also proposed as an important mechanism for subsurface wear. The large amount of strain imposed on the material also induced martensitic phase transformation. Fragmented erodent particles and oxide film were found embedded into the material which caused formation stress concentrated regions in the material and contributed to crack initiation. A composite structure is formed consisting silicon oxide sand particles and chromium oxide film along with the martensitic phase transformed metal. The corrosive environment is also believed to have played a significant role in the initiation and propagation of cracks. Crack initiation and propagation due to the mechanical and electrochemical processes enhances the material mass loss as the crack networks coalesce and subsequently cause material spalling. Physical models are developed based on these observations to explain the microstructural changes and synergistic mechanisms.     

Correlation between solid particle erosion of cermets and particle impact dynamics

Since the erosion rate depends on energy exchange between particle and material, a reformulation and solution of the equations of two solid bodies collision is presented and adapted to the calculation of the energy absorbed by a material surface during impact of a spherical particle onto a plain target. It has been observed that energy loss is a strong function of dynamic coefficients named as coefficient of velocity restitution after impact, k, and coefficient of dynamic friction, f. The new method and experimental equipment for the coefficients determination are described. It was shown that energy consumption during application may be an appropriate guide for the material selection in the conditions of erosive wear.     

Understanding particle dynamics in erosion testers—A review of influences of particle movement on erosion test conditions

An understanding of particle dynamics is important when determining material erosive wear in any erosion tester, because particle impact conditions are primarily influenced by particle acceleration. A better understanding of particle dynamics in the testers will aid the control of erosion test conditions and therefore improve the accuracy of measurement. In this paper, particle dynamics in the two most popular erosion testers, the centrifugal erosion tester and the gas-blast erosion tester, has been discussed in detail. Mechanisms of particle acceleration in the two types of testers were explored and computational models of particle dynamics were described briefly. A review of the experimental determination of important characteristics of particle dynamics (such as particle velocity, particle trajectory, particle dispersion and particle rotation) showed how they influenced particle movement and therefore the particle impact conditions. In addition, comparison of the particle dynamics in the two types of erosion testers showed that differences of particle acceleration may lead to significantly different results at identical pre-set test conditions. It may be concluded that it is not possible to directly compare the results obtained in different types of erosion testers even under notionally identical test conditions.     

Full factorial investigation on the erosion-corrosion resistance of UNS S31603

The interactions that occur when erosion and corrosion act simultaneously are extremely complex and are often difficult to interpret. These interactions generate either a synergistic or antagonistic material loss effect for a particular material in a certain environment. The level of interaction between impact energy, number of impacts, fluid temperature, material properties, fluid flow and electrochemical properties severely complicates the analysis of erosion-corrosion wear rates. This paper investigates the interaction between the main parameters influencing erosion-corrosion. A combination of statistical analysis and interaction contour plots has been employed to obtain in-depth understanding of the variables influencing erosion-corrosion, namely particle velocity, sand size, sand concentration and fluid temperature. An empirical equation has been derived from test results to describe the relationship between the test parameters. Analysis of the residuals versus predicted erosion-corrosion shows a normalized distribution and thereby confirms the suitability of this model. Velocity was found to have the strongest influence on erosion-corrosion rate followed by sand concentration, temperature and finally sand size, which had the least significant effect. SEM surface features show that the increase in sand concentration causes the surface to be covered with a higher number of impact craters and lips indicating a linear relationship between the two. The SEM micrographs also show that the increase in sand size produces deeper craters and more prominent lips compared to fine sized particles where the particles tend to graze the surface without sufficient kinetic energy to plastically deform the material surface.     

The effects of manganese content and mould size on abrasion and slurry erosion behaviour of chromium–manganese iron systems investigated by positron lifetime spectroscopy

Abrasion and slurry erosion behaviour of chromium–manganese iron samples with chromium (Cr) in the range 16–19% and manganese (Mn) at 5 and 10% levels have been characterized for hardness followed by microstructural examination using optical and scanning electron microscopy. Positron lifetime studies have been conducted to understand the defects/microporosity influence on the microstructure. The samples were heat treated and characterized to understand the structural transformations in the matrix. The data reveals that hardness decreased with increase in Mn content from 5 to 10% in the first instance and then increase in the section size in the other case, irrespective of the sample conditions. The abrasion and slurry erosion losses show increase with increase in the section size as well as with increase in Mn content. The positron results show that as hardness increases from as-cast to heat treated sample, the positron trapping rate and hence defect concentration showed opposite trend as expected. So a good correlation between defects concentration and the hardness has been observed. These findings also corroborate well with the microstructural features obtained from optical and scanning electron microscopy.     

Coriolis flowmeters: a review of developments over the past 20 years,and an assessment of the state of the art and likely future directions

This paper starts from a brief revisit of key early published work so that an overview of modern Coriolis flowmeters can be provided based on a historical background. The paper, then, focuses on providing an updated review of Coriolis flow measurement technology over the past 20 years. Published research work and industrial Coriolis flowmeter design are both reviewed in details. It is the intention of this paper to provide a comprehensive review study of all important topics in the subject, which include interesting theoretical and experimental studies and innovative industrial developments and applications. The advances in fundamental understanding and technology development are clearly identified. Future directions in various areas together with some open questions are also outlined.     

Effect of impact angle on the slurry erosion–corrosion of 304L stainless steel

This communication describes an investigation of the effect of impact angle on slurry erosion–corrosion of stainless steel using a new slurry erosion rig. With the new apparatus, it is possible to measure the individual erosion events under impact as both electrochemical current/time transients, and mechanical transients through acoustic emission (AE) simultaneously. Each sharp rise observed in the electrochemical current transient under particle impact is accompanied by an AE event. These sharp current rises are attributed to the rupture or removal of the oxide film on the surface by the abrasive particles. The correlation between the current rise and the maximum of the AE event, although scattered, shows an increase with decreasing impact angle. The current transients due to individual erosion events show that on the average, the current rise is greater and the rise time is longer at oblique angles compared with those at normal incidence. The degree of denudation of the metal surface by individual particle impingements, the process which strips the surface of its passivity, increases at more oblique angles. Weight loss measurements demonstrate that the synergistic effect between erosion and corrosion is enhanced by a more oblique angle of impact. The origin of the synergism is discussed.     

Influence of microstructure on erosion resistance of steels

Erosive wear due to solid particle impingement is a very intensive degradation process of surface layers of metallic materials. Erosion resistance is influenced by the working conditions (impact angle, impact velocity of solid particles, size, shape, hardness and amount of impinging particles) and the parameters of the worn material like hardness and microstructure. In our experiments some structural and tool steels were tested by slurry with SiO₂ particles at a flow velocity of 20 m/s. The microstructures of the tested steels were modified in a broad range by changing the conditions of their heat treatment. Increasing pearlite share in the structure of annealed carbon and low-alloyed steels has a positive effect on their erosion resistance. The growing carbon content in the tested hardened steels increases their erosion resistance. Maximum erosion resistance was found in hardened chromium ledeburite steel. Hardened high-speed steel HS 11-0-4 in spite of its high hardness has lower erosion resistance than ledeburitic chomium steels. An increasing amount of retained austenite and decreasing carbide and martensite shares with growing quenching temperature of the tested ledeburitic chromium steels leads to the reduction of their erosion resistance.     

Effects of Cr3C2 addition on the erosion–corrosion resistance of Ti(C,N)-based cermets in alkaline conditions

Effects of Cr₃C₂ on the erosion–corrosion behavior of Ti(C,N)-based cermets are studied in alkaline conditions. The results indicate that the erosion–corrosion resistance of cermets is improved with proper Cr₃C₂ content. Corrosion performance of cermets is deteriorated by Cr₃C₂ addition in NaOH solution. With the increase of Cr₃C₂, the erosion–corrosion behavior of Ti(C,N)-based cermets is classified to be erosion regime, erosion–corrosion regime, corrosion–erosion regime and corrosion regime. Materials degradation is determined by particles erosion for cermets with low Cr₃C₂ content, while for materials containing more Cr₃C₂ addition, binder corrosion and subsequent erosion are responsible for materials deterioration.     

Cavitation erosion resistance of Cr–N coating deposited on stainless steel

Results of investigation on cavitation-erosion resistance of Cr–N coating deposited on stainless steel X6CrNiTi18-10 (1H18N9T) by means of the cathodic-arc method are presented. The evaluation of Cr–N coating resistance to cavitation erosion is based on the investigation performed in a cavitation tunnel with a slot cavitator and tap water as a medium. The investigation was performed at variable-cavitation intensity and the estimated cavitation resistance parameters of coatings were the incubation period of damage and the instantaneous erosion rate after exposure of specified duration. It has been confirmed that the incubation period of the Cr–N coating damage is approximately 50% longer than that of the uncoated X6CrNiTi18-10 steel, and the instantaneous erosion rate after exposure of specified duration is comparable in both cases. The scanning microscope analysis indicates that the damage of Cr–N coating is due mainly to its delamination, while the erosion of deeper parts of the coating is of minor importance. The character of the coating and substrate damage in multiple locations indicates that the hard coating microparticles torn-off during the cavitation bubbles implosion hit against the coating and the revealed areas of substrate. As a result, the coating and especially the substrate of relatively low hardness are subject to cavitation erosion and to solid particle erosion with the hard torn-off microparticles of coating. The results of the investigation and the analysis indicate that the factors mainly responsible for a long incubation period and low cavitation erosion rate of the steel substrate/hard coating systems are the gained high hardness of substrate and high level of coating adhesion.     

Solid particle erosion of unidirectional fibre reinforced thermoplastic composites

In the present study, the solid particle erosion behaviour of neat PEEK matrix and unidirectional glass fibre (GF) and carbon fibre (CF) reinforced polyetheretherketone (PEEK) and polyetherketoneketone (PEKK) composites has been studied. The erosion experiments have been carried out by using silica sand particles (200 ± 50 μm) as an erodent. Steady state erosion rates of these composites have been evaluated at different impact angles and impact velocities. The neat PEEK exhibited peak erosion rate at 30° impingement angle whereas the composites exhibited a semi-ductile behaviour with peak erosion rate at 60° impact angle. The erosion rate of the glass fibre reinforced composites was higher than that of the carbon fibre reinforced composites. The results show that the fibre orientation has a significant influence on erosion rate only at lower impact angles. The erosion rate of the composites was higher when the particles impact perpendicular to the fibre direction than parallel to the fibres. The morphology of eroded surfaces was observed under scanning electron microscope and damage mechanisms were discussed.