Published: Jan 2007
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EROSION IS DIFFERENT FROM WEAR IN THAT there is a fluid contribution to the mechanical action that is producing wear. If the fluid is corrosive to the material being eroded, it will increase material removal. Water is often corrosive in erosion on metal base systems so there will be a contribution. On the other hand, air in solid particle and droplet erosion is not corrosive to most materials so there will not be a “dissolution component.” When a fast-moving stream erodes a canyon through solid rock there may or may not be a corrosion component depending on the type of rock. Water in copper plumbing can certainly have a chemical component. In fact, any of the metals that rely on passive films for corrosion resistance are likely to be corroded when the mechanical action of the fluid or particles in the fluid disrupts the film formation kinetics.
This chapter will describe some of the tests that are commonly used to research erosion processes and rank engineering materials for use in erosive applications. Retrieving oil from hundreds/thousands of meters below ground always produces erosion of the drilling tools. Handling coal in mining and again in coal-fired boilers produces erosion. Venting sand/dirt-laden air erodes fans and impellors. Droplets impacting aircraft erode affected surfaces. And, of course, working soil as in farming erodes tillage tools. Thus, erosion is very widespread and of great economic importance. Hopefully, this chapter will provide people who are confronted with solving erosion problems a path forward. This chapter will discuss tests for the major forms of erosion, solid particle, slurry, droplet, impingement, cavitation, and erosion corrosion. Standard tests will be described where they are available.
As a repeat of the definition in Chapter 2, solid particle erosion is material removal/damage to a solid surface produced by repeated impacts of solid particles. Sand blasting is the most common example. Holding a sandblast nozzle a short distance from a steel surface and impinging it on the surface will erode a hole through the steel plate if allowed to impinge for a length of time. It is erosion by our definition because it involves the mechanical action of a fluid. The gas propellant imparts kinetic energy to the particles and that energy is expended in deformation and fracture on impact.