Erosion concerns deal with the ability of a selected material to resist the wear that results from the impingement of dirt, scale, sand, vapor droplets, or other small particles on critical valve surfaces.
Conditions For Erosion – Erosion is the result of many factors. Figure 22 illustrates the major factors that influence the potential for erosion damage.
Erosion And Corrosion – Erosion and corrosion often occur simultaneously. Many materials gain corrosion resistance from a passive layer of oxides that form on the material surface. If this layer is damaged or removed by erosion, then corrosion and erosion work together to remove material from the surface of the affected component.
Erosive Applications – The potential for erosion damage is generally greatest in applications that are near the wellhead because the fluids typically carry sand, dirt, gravel, and scale; however, it is common for fine grit and other particulates to remain in the fluid stream even in intermediate refinery and gas plant processes. Vapor droplets can also result in erosion damage. Vapor droplets are common in steam applications, and in flashing liquids.
Evaluating The Potential For Erosion Damage – Unfortunately, there is no standard scale on which the potential for erosion damage can be empirically measured, and there is no absolute guideline for material selection. Experience and professional engineering judgment must be applied when selecting materials for erosive applications.
Material Selection – Figure 23 lists some of the materials that are commonly specified for erosive applications. In general, the materials are listed in the order of increasing erosion resistance. In addition to erosion resistance, specifiers must also evaluate materials in terms of their corrosion resistance, strength, temperature limits, and other material properties.