Tribology matters

Tribology touches every aspect of our day to day existence and the wonder of this is that we are completely unaware how central it is to how we function. Take a snapshot of thebeginning of a normal working day for example. A typical morning start will involve brushing one's teeth with toothpaste containing mild abrasive (with a toothbrush with an optimized design for brushing efficiency), using a shampoo and conditioner which have been tested for frictional properties on a wide range of hair types, and for those who have the traditional morning fry up - lubricating the pan in advance with cooking oil to provide a boundary layer between the food and the pan and to reduce adhesion and heat transfer. It is clear that tribology plays a major role in our everyday lives. Whether starting out for work by foot, bicycle or car, friction will define whether our shoes or tyres can grip the road surface and whether the brake or clutch will do their job. If it is raining, the speed limit is modified in some countries, testifying to the influence of tribologists in decision making in the transport industries

Tribo-corrosion maps for application in bio-tribology : some new approaches

Advances in the study of tribo-corrosion of materials in recent years have included the development of mechanistic maps, showing the transitions between the regimes as a function of the main process parameters. In such cases, maps have been constructed in both two and three dimensions. There are now a variety of modelling algorithms which may be used to map a range of performance indicators over a multi-parameter space. The interactions of tribo-corrosion in biological environments are becoming of increasing importance

Erosion-corrosion maps for carbon steel in crude oil/water slurries : impact angle and applied potential effects

In studies of erosion-corrosion, there have been few investigations into the effect of tribological issues, such as particle impact and impact angle, on erosion-corrosion of materials in oil field production. Despite this fact, erosion-corrosion in such environments is a major issue. In such conditions, it is important to define regimes where the effect of lubricating oil may modify the erosion properties of the materials. In this study, the combined effects of erosion and corrosion were investigated in three environments, crude oil (high API gravity 52), reservoir water, and 20% reservoir water with crude oil at a range of applied potentials. Erosion-corrosion maps were constructed, based on the results, showing the change in mechanisms and wastage rates as a function of impact angle and applied potential. Regimes of erosion-corrosion were described on such maps using such an approach. From this work, it can be seen that the corrosion contribution was increased with an increase in the percentage of reservoir water. In the crude oil environment, it was shown that the erosion contribution (Ke) was generally higher than that for corrosion suggesting that corrosion was reduced in crude oil. The results are interpreted in terms of the effect of the crude oil environment in modifying the impact properties of the particles therefore providing surprising resistance to particle impacts in nominally aggressive corrosion environments

Mapping erosion-corrosion of carbon steel in oil exploration conditions : some new approaches to characterizing mechanisms and synergies

Erosion by solid particles in oil/water slurries is a technologically important area. In such conditions, it is necessary to distinguish between the effects of the sand, aqueous environment, and the oil. Erosion-corrosion maps provide a means of identification between erosion-corrosion regimes as a function of erosion and corrosion parameters. However, there has been no work carried out to map the effects of parameters in oil/water slurries. This paper investigates the effect of erosion-corrosion on carbon steel in oil field production and maps the results. Distinctions between "synergistic" and "additive" erosion-corrosion behaviour are superimposed on the maps in the various environments

A note on threshold velocity criteria for modelling the solid particle erosion of WC/Co MMCs

The threshold velocity for erosion of a ductile material is considered as the velocity required for initiation of plastic deformation in the substrate. For a brittle material, it defines the velocity required to nucleate a median crack in the elastic/plastic interface beneath the indentation. By invoking models for the solid particle erosion of ductile and brittle materials from the literature, together with a set of criteria based on threshold velocity calculations for erosion of the individual components, various predictions of erosion behaviour of WC/Co MMCs have been made. Qualitative agreement was found between the model predictions and various trends of the solid particle erosion behaviour of WC/Co cermets in the literature. The implications of the findings in addressing some of the puzzling trends of the solid particle erosion of MMCs in the literature, and how such insights may result in a reconsideration of some "classical" solid particle erosion relationships, are addressed in this paper

Wear maps for TiC composite based coatings deposited on 303 stainless steel

Dry sliding wear (pin-on-disc) tests were carried out under ambient conditions at room temperature for TiC coated and uncoated 303 stainless steel, using alumina as a counterface. The composite coating which was developed by Tungsten Inert Gas (TIG) methods increased the surface hardness of the substrate and the sliding wear resistance of the substrate. Wear maps for both uncoated and coated materials were developed on the basis of tests results. The results indicated that the role of oxidative wear differed significantly for both coated and uncoated materials on the wear map. In addition, it was found that TiC composite coatings not only increased the wear resistance but also expanded the mild wear region towards higher loads and sliding speeds

CFD modelling of erosion-corrosion of steel in aqueous environments : particle concentration effects on the regime boundaries

In this study, a new methodology is used to model the effects of particle concentration on the inner surfaces of a circular pipe 90º bend, assuming applied potential controlled aqueous slurry flow at room temperature. This enables the regimes of the component to be mapped according to the intensity of erosion and corrosion contributions. The results show that for a constant inlet particle concentration, it is shown how transitions between erosion-corrosion regimes are observed around the pipe. For increases in particle concentration, significant variation of the erosion-corrosion regimes are observed, with a reduction of the corrosion dominated regime. The results are interpreted in the terms of the changes in local erosion conditions along the component in the flowing environments. Typical results from the model are shown illustrating how this new mapping method can be used effectively to optimize process conditions and materials in such environments

A new methodology for modelling erosion–corrosion regimes on real surfaces : Gliding down the galvanic series for a range of metal-corrosion systems

Erosion-corrosion of materials in aqueous environments is a complex phenomenon involving a very large number of variables. In such cases, characteristics of the target, particle and the environment affect the degradation mechanism. Predicting material behaviour may sometimes be a "black art" due to the parameter size which is involved in such processes. In studies of erosion-corrosion, there have been significant advances in the modelling of such processes in recent years. Various methodologies employed include quasi-static modelling, using CFD modelling and erosion-corrosion mapping. In such cases, the output of the various models can differ significantly. In this work, a methodology combining CFD modelling and erosion-corrosion mapping has been developed to model erosion-corrosion behaviour of pure metals, which variously passivate and dissolve under a range of simulated conditions. This provides a means of mapping the component undergoing erosion-corrosion and thus is a step change on previous modelling work in this area as it enables superimposition of the erosion-corrosion map on real surfaces. The relative advantages and limitations of this approach are discussed in this paper

Some comments on mapping the combined effects of slurry concentration, impact velocity and electrochemical potential on the erosion–corrosion of WC/Co–Cr coatings

Materials exposed to aqueous slurry environments must not only resist the impact of solid particles and the flowing environment but also the degradation caused by electrochemical corrosion. In this study, the combined effects of slurry particle concentration and velocity on the erosion-corrosion of a WC/Co-Cr coating were assessed at a range of electrochemical potentials in a synthetic sea water solution containing sand particles and compared to the performance of a mild steel exposed to similar conditions. The erosion and corrosion contributions and their interactions were evaluated for the materials. The results indicated that the erosion-corrosion mechanism of the coating and the mild steel showed significant differences when particle velocity and concentration were increased at various potentials. For both materials, degradation mechanisms were identified and superimposed on erosion-corrosion maps. Maps indicating levels of wastage, extent of synergy between the processes and the optimum material performance were also generated as part of this study. Scanning electron microscopy was used to confirm the degradation regimes and mechanisms of material removal during the erosion-corrosion process

A map and a pipe : a new approach to characterizing erosion-corrosion regimes of Fe in three dimensions using CFD modelling

In studies of erosion-corrosion, much work has been carried out in recent years to identify regimes of behaviour. Such regimes describe the transition between the erosion and corrosion dominated mechanisms. They can also be used, by assigning various criteria, to identify other regimes of behaviour such as extent of "synergy/antagonism" in the process, so-called "additive" behaviour and the extent of wastage. Despite this work, there has been very little effort to combine the two dimensional erosion-corrosion map with CFD modelling approaches, in which the characteristics of the fluid are accounted for in the regime description. This means that extrapolation of such maps in two dimensions to a three dimensional real surface presents some difficulties. However, it is these surfaces that corrosion engineers are required to tailor, either through modification of the material composition, the surface or the process parameters, for optimum erosion-corrosion resistance. In this paper, a methodology is generated to combine the concepts of CFD modelling, and the erosion-corrosion regime map for a specific geometry and for a range of pure metals in descending order in the Galvanic series. The changes in regimes are presented as a function of variation in the erosion and corrosion variables i.e. particle size, hardness and solution pH. Erosion-corrosion regimes are presented, based on the model results, showing the wide range of mechanistic and wastage mechanisms possible over the component surface