Development of Corrosion Assessment Diagrams for High Temperature Chlorine Corrosion Part II: Development of “Dynamic” Quasi-stability Diagrams

Abstract

The corrosion of metals at high temperatures in halogen containing environments differs from most other types of high temperature corrosion in that in addition to solid and liquid corrosion products volatile phases are also formed. The latter are not covered by the usual thermodynamic stability diagrams, which are often used for prediction of the corrosion products formed, and indirectly on whether corrosion has to be regarded as critical or not. The present paper aims at including the situation where gas phase corrosion products determine the extent of corrosion and a new type of diagram is developed and discussed for the example of chlorine containing environments. Part I of this paper (Latreche et al. Oxid Met 2009) was dedicated to the establishment of the basis for a new extended approach to a corrosion risk assessment diagram called the ''dynamic'' quasi-stability diagram. The present part deals with the principles of the new type of diagram and the establishment of specific diagrams for the most common alloying elements, i.e. Fe, Ni, Mo, Cr, Si, Al. For the development of the specific diagrams, the calculation of gas viscosities and gas diffusion coefficients of all relevant volatile potential corrosion products was conducted, with methods specified in the paper. The new ''dynamic'' quasi-stability diagrams were then compared to experimental results from kinetics investigations of pure metals, which showed quite good agreement with the experimental observations. Furthermore, the diagrams were used to assess H. Latreche the behaviour of the metallic elements in alloys. Again, in this case good agreement between prediction and experimental results was observed if the specific role of the different elements in the corrosion behaviour of the alloys was taken into account.

High temperature corrosion during biomass firing: improved understanding by depth resolved characterisation of corrosion products

“…Such a cyclic corrosion mechanism caused by Cl is termed the 'chlorine cycle' and is chiefly responsible for the active oxidation of steels in Cl-containing environments. 33,35 Following such a mechanism, the likely oxides to be observed in a Fe-Cr-Ni alloyed steel (similar to the alloy investigated in the present work) are the Fe and Cr oxides. This is because the alloying elements, Fe and Cr have a higher affinity for Cl(to generate metal chlorides), relative to that of Ni .…”

Performance of NiCrAlY Coatings Deposited by Oxyfuel Thermal Spraying in High Temperature Chlorine Environment

“…In previous investigations (Ref 35), the experimental gas components (O 2 and Cl 2 ) are shown to be the species with the highest diffusion coefficients. Among these two species, O 2 diffuses more rapidly; the diffusion coefficient at 1000 K for O 2 is 1.55 cm 2 /s, while at the same temperature Cl 2 diffuses with 0.96 cm 2 /s in the gas mixture.…”

Effect of flue gas composition on deposit induced high temperature corrosion under laboratory conditions mimicking biomass firing. Part I: Exposures in oxidizing and chlorinating atmospheres

“…. It is important to note that for the Fe–Cl 2 –O 2 diagram, the line separating solid metal chloride and gas metal chloride phases, only represents the maximum limit for the solid metal chloride because volatile metal chlorides may exist at chloride partial pressures below this limit . According to Fig.…”