Flow accelerated corrosion

Keywords FAC- Flow accelerated corrosion HRSGs-Heat recovery steam generators AVT(R) - All volatile Reducing treatment... 

If the critical shear stress that acts on the layer of corrosion products present at a surface is exceeded, mechanical film damage leads to a strong increase in the rate of corrosion. According to this view, stainless steel and titanium are not susceptible to flow accelerated corrosion because the thin passive oxide films formed on these metals are more resistant to shear stresses than the corrosion product layers found on copper and its alloys [16]. 

Unfortunately, no experimental proof has been given so far that flow accelerated corrosion is the result of exceeding a critical shear stress that acts on protecting surface films of corrosion products. Rather, a number of studies suggest that flow accelerated corrosion can be explained simply based on mass transport considerations [17]. 

A sound design of fluid flow systems reduces the risk of flow accelerated corrosion (Chapter 10). Most important is to avoid sudden changes in flow direction at sharp bends. As a rule of thumb, the radius of a pipe bend carrying an aqueous fluid should be greater or equal to three times the pipe diameter (Figure 12.3). 

Figure 12.3 Reduction of the risk of flow accelerated corrosion at an elbow the risk is greater for the configuration (a) than for that of (b).

Chexal, B., Horowitz, J., Jones, R., Dooley, B., Wood, C., Bouchacourt, M., et al., Flow-Accelerated Corrosion in Power Plants, EPRI and Electricite de France, Palo Alto CA, 1996, pp. 4-11,... 

Efird, K. D., "Jet Impingement Testing for Flow Accelerated Corrosion, CORROSION/2000, NACE Annual Corrosion Conference, 2000, Paper No. 2000. 

Feedwater, Condensate, and Boiler Water (general and flow accelerated corrosion)... 

In environmental simulations in laboratory testing, the corrosion potential and pH are the most important variables. The difference between oxidizing and reducing conditions is important for all types of corrosion (in particular for stress corrosion, corrosion fatigue, and flow accelerated corrosion). 

Equipment exists to also monitor the temperature pH, corrosion and redox potentials, and the corrosion hydrogen that is always produced during corrosion by aqueous solutions [35]. Periodic analysis of condensate, feedwater, and boiler water samples for iron and copper gives a good indication of general corrosion and flow accelerated corrosion. 

Flow-Accelerated Corrosion in Power Plants, EPRI, Palo Alto, CA, 1998, TR-106611-R1. 

A physical model for flow-accelerated corrosion is shown in Figs. 6-13 and 6-14. 

Recently, terms flow-assisted corrosion and flow-accelerated corrosion (FAC) have been used to describe the erosion (or thinning) of carbon steel in nuclear and fossil power plants where there is no threshold solution velocity. FAC is a complex phenomenon that is a function of many parameters of water chemistry, material composition and hydrodynamics. FAC involves the electrochemical aspects of general corrosion plus the effects of mass transfer and momentum transfer. 

With the exception of cavitation, flow-induced corrosion problems are generally termed erosion-corrosion, encompassing flow enhanced dissolution and impingement attack. The fluid can be aqueous or gaseous, single or multiphase [23]. There are several mechanisms described by the conjoint action of flow and corrosion that result in flow-accelerated corrosion (FAC) [24 25] ... 

Figure 6.37 Pipe wall thinning (a) and corrosion patterns (b) caused by flow accelerated corrosion (FAC) inside a steam line. (Courtesy of Russ Green, TMI)...

Chexal B, Horowitz J, Dooley B, Mfllett P, Wood C, Jones R. Flow-Accelerated Corrosion in Power Plants, Revision 1. EPRI TR-lO ll-Rl. Palo Alto, Calif. Electric Power Research Institute, 1998. 

HRSG flow-accelerated corrosion Combustion turbine 10 0.09... 

Erosion-corrosion (flow accelerated corrosion) Piping components Thinning rate for materials of concern in the specific suspected areas of piping... 

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