Chapter 9 - Erosion corrosion

Abstract

Erosion is a process by which individually separated small solid particles with the tendency to remain still and/or impact liquid droplets strike the surface of a material to cause damage and metal loss. The wall thickness of the piping and valve is reduced owing to the effect of erosion in the same manner as the effect of sweet or carbon dioxide corrosion. Erosion-corrosion is a combination of erosion and corrosion that has been used to explain the internal surface damage and dissolution under corrosion of components such as valves owing to the internal fluid service and loss rates under solid particle erosion. The severity of erosion depends on various factors such as the size, type, and material of sand particles; material and shape of steel exposed to erosion; and fluid flow factors like velocity and turbulence. Different approaches are used to mitigate erosion damage, such as selecting hardfacing materials, limiting the fluid flow velocity, and using erosion allowance. This chapter discusses two case studies. The first one is to prevent erosion damage in valves located upstream and downstream of the first stage separator on an offshore platform. Erosion allowance of 2mm has been added to the internal thickness of these valves to prevent erosion damage owing to the sandy service. The second case study reviews various types of valves (mainly super duplex or low-alloy steel with 3-mm Inconel 625 cladding (weld overlay)) used in the subsea oil and gas industry on manifolds that are exposed to a high risk of erosion because of a fluid service containing particles. Some subsea valves are used in extremely dirty services; therefore, 2-mm erosion allowance should be added. In such cases, the Inconel 625 weld overlay thickness should be increased from 3 to 5mm.