Erosion-corrosion prediction

Basically there are two approaches to predicting the occurrence of erosion corrosion. Practical or experience based methods typified by Keller s approach for carbon steels in wet steam. Keller developed an equation that related the erosion corrosion rate as a function of temperature, steam quality, velocity and geometric factor. In recent years this approach has... 

Toughness can influence the performance of materials under conditions of erosion-corrosion. The soft metals are often more susceptible to erosion corrosion because they are more susceptible to mechanical wear. The toughness is a good criterion for the resistance to the mechanical erosion or abrasion, but this is not necessarily a good criterion to predict the resistance to the erosion-corrosion. Stellite (Co-Cr-W-Fe-C alloy), which has better toughness than 18-8 stainless steel, showed better resistance to cavitation erosion on a water brake.25... 

The velocity profiles and transverse momentum transfer close to the solid/liquid interface dictate wall shear stress levels and mass transport efficiencies, both of which are important drivers for erosion-corrosion. Therefore, critical velocity values are very geometry-specific and cannot be readily applied to predict component service life in generic flow systems. 

However, the ability to predict or map erosion-corrosion relies on including the correct mechanisms and material responses (i.e., phase transformations). 

Materials selection plays an important role in minimizing erosion corrosion damage. Caution is in order when predicting erosion corrosion behavior on the basis of hardness. High hardness in a material does not necessarily guarantee a high degree of resistance to erosion corrosion. 

B. D. Craig 1998. Predicting critical erosion-corrosion limits of alloys for oil and gas production. 

In order to predict the direction of corrosion and mass transfer, it is essential to have data on thermodynamic properties of chemical compositions and steel components as a function of temperature. If the liquid metal is flowing at high velocity, the material is subject to erosion. Formation of the film (consisting of both steel and liquid metal coolant components) on the structural metal surface is another type of corrosion, since this is not protective film. Due to the difference in chemical activity between sodium and lead, technologies of these coolants are quite different, although some methods share a number of common features. 

Escalation as rapid as this cannot be caused by the corrosion-erosion or overheating mechanisms described above. An external mechanical cause either from a seismic event, impact of a foreign body, or sudden catastrophic failure of a tubeplate, would be needed. To predict the consequences of such an event in which the sodium side of an SGU is suddenly raised to the steam-side pressure, the flow and pressure in the secondary circuit and the protective systems have to be calculated taking account of the compressibility of the sodium. 

Commercial cyclone installations are usually subject to a performance evaluation after they are brought on-line and process conditions have stabilized. Such Start-of-run measmements may be performed to verify vendor performance predictions or, a closely related objective, to determine if the cyclone(s) are performing their intended process duty. Aside from these important reasons, early in-the-run performance measm-ements also provide a benchmark with which to compare preformance later in the run. cyclone performance will usually deteriorate with rim time in coimnercial systems since they are normally required to run for months or even years between turnarounds. Such deterioration may be due to a munber of factors erosion (increased wall roughness or holes in walls), corrosion, weld cracking, deposit formation, distortion, seal problems, etc. (see related discussion in Chap. 12). Periodic performance measurements allow plant persoimel to detect and monitor the rate of performance degradation and thereby estimate its useful remaining run life. 

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