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ABSTRACT Erosion-corrosion is an important aspect of durability for materials used in the oilsands industry. The combination of a corrosive fluid and high volume of sand means that erosion, corrosion and their synergistic interactions all act to accelerate material damage. Material degradation rates are typically controlled by use of surface engineering or by use of hard alloys such as those studied in this paper. The high chromium Cast White Irons (CWIs) are an important class of material for components used for slurry handing apparatus in the oilsands process. In this paper results from an evaluation of corrosion and combined erosion-corrosion are reported. Erosion processes accelerate corrosion and the extent of the acceleration is dependent on the alloying of the CWI. However, it is found that the ranking of the three CWIs tested was common when assessing corrosion and combined erosion-corrosion degradation. The degradation in erosion-corrosion is primarily by matrix extrusion from a mechanical point of view. Corrosion processes act to accentuate that mechanism of damage. INTRODUCTION Separating oil from sand is a unique combination of mining and oil processing. Every day huge amounts of oil-saturated sand is dug in open pit mining operations in Alberta, Canada. Huge shovels, dump trucks and hydrotransport are the principal means by which oilsand slurries move the sand to the extraction process. The multi-stage efforts remove and clean a slick tar-like substance known as bitumen, the main feedstock for petroleum products [1-3]. Throughout the process, plant parts and materials must withstand extreme conditions such as high temperature and high pressure. They are faced with a host of degradation processes like abrasion, erosion, corrosion and fatigue. This results in reduced lifetimes for certain components and associated high maintenance costs are experienced. It is estimated that damage due to wear costs the world's largest oilsands producer over $ 450 million annually [2, 3]. In order to reduce operating costs, materials research and design modifications have been carried out to improve equipment run life. Numerous material selection strategies are needed for varied applications because there are always trade-offs between other properties such as corrosion resistance, toughness, strength, wear resistance, etc. In the oilsands industry one of the key degradation processes is erosioncorrosion and the complexities of this are such that material selection strategies have not yet been optimised. Alternative materials are often required to combat erosion-corrosion. Because in some cases, corrosion processes magnify material degradation by erosion processes [1, 4] and vice versa it is not always clear what the key material selection criteria should be. As a result it is important to understand how materials behave in the erosion-corrosion environments in which they are used. High-alloy white irons are primarily used for abrasion-resistant applications and are readily cast into the parts needed in machinery for crushing, grinding, and handling of abrasive materials. The chromium content of high-alloy white irons also enhances their corrosion-resistance. High-chromium Cast White Irons (CWI) can be described as composites with large, hard proeutectic or eutectic M7C3 carbides in a softer matrix [5,6].
- North America > United States (0.46)
- North America > Canada > Alberta (0.34)
Study of corrosion in erosion-corrosion of two stainless steels in simulated marine conditions via experimental design
Meng, H. (Corrosion and Surface Engineering Research Group, School of Mechanical Engineering, University of Leeds) | Hu, X. (Corrosion and Surface Engineering Research Group, School of Mechanical Engineering, University of Leeds) | Neville, A. (Corrosion and Surface Engineering Research Group, School of Mechanical Engineering, University of Leeds)
ABSTRACT ABSTRACT The corrosion behavior of two stainless steels (UNS S32760 and UNS S31603) for marine applications has been assessed under liquid-solid impingement conditions in 3.5% NaCl. The corrosion rate and the amount of material degradation due to corrosion and corrosion effects on erosion have been determined under various conditions. The three environmental parameters considered in this study are solid loading, flow velocity and temperature. A full two-level factorial experimental design method was applied to study the individual effects of each parameter as well as their interactive contributions to corrosion and the effect of corrosion in erosion-corrosion. From the analysis, velocity shows the greatest effect on the corrosion rate of both materials, followed by solid loading, temperature, and interactive effects of temperature-velocity and solid loading-velocity. However, the most effective contributions to the corrosion effect on erosion, often denoted synergy, are mainly from velocity, solid loading and the interactive effect of solid loading and velocity. In this paper, the corrosion behavior of two stainless steels and the mechanisms of material degradation under different experimental conditions will be discussed. INTRODUCTION Year year year corrosion causes rapid material degradation in marine environments, and millions of dollars are spent to repair material damage in marine industries every year. Marine corrosion continues to cause mundane failures everyday, which lead to downtime of sub-sea systems, material wastage, energy inefficiency and large costs to industry. In the oil and gas sector it is condition for corrosion to occur in partnership with erosion as large flow velocities and solid-laden fluids are encountered. This makes long term material performance even more challenging. In 1912 English metallurgist Harry Brearley invented stainless steels in his search for an alloy to protect cannon bores from erosion; stainless steels still play a very important role in industry and still offer good resistance to erosion-corrosion. It is well known that stainless steel is one of the prominent corrosion resistant alloys due to a tightly adherent, stable and self-healing film on the surface to provide a barrier to charge transfer between the relatively active bulk material and the corrosive environment. But solid particles are entrained, the protective film can be removed by mechanical wear or bubble collapse during the impingement process. Where the films are mechanically removed, charge transfer can occur at the steel/water interface without retardation from the barrier film. Technical developments over the decades have improved the standard grades invented in the 1920s with higher strength, higher corrosion resistance and lower maintenance. A wealth of recorded data contributes to the excellent understanding of stainless steels' corrosion behavior and corrosion mechanisms. Erosion-corrosion in aqueous systems is dominated by two major mechanisms: electrochemical corrosion and mechanical erosion. On account of the greater material loss from erosion-corrosion than the sum of their individual contributing components, the interaction between electrochemical and mechanical processes has been recognized in many works, and they have been referred to as 'Synergistic' and 'Additive' effects. The so-called synergistic effect is normally used to describe the way in which corrosion can enhance erosion, while the so-called additive effect refers to the mechanism by which erosion can enhance corrosion.