DECHEMA

About: DECHEMA is a nonprofit organization based out in Frankfurt am Main, Germany. It is known for research contribution in the topics: Corrosion & Oxide. The organization has 756 authors who have published 1307 publications receiving 25693 citations.

Development of Corrosion Assessment Diagrams for High Temperature Chlorine Corrosion. Part I: State of the Art and Development of the Basis for a New Extended Approach

Abstract: As in many other areas of material science there is an increasing need for computational tools predicting materials behaviour, also in high temperature corrosion. In many cases stability diagrams have been developed for the assessment of high temperature corrosion resistance of metallic materials where the potentially formed corrosion products are plotted as fields of stability as a function of the activities or partial pressures of the species in the reaction environment. One major drawback of these diagrams is that they only contain solid or liquid phases as reaction products, but in halogen induced high temperature corrosion volatile metal halides are also formed. In order to overcome this drawback, the present paper deals with the development of a new type of diagram for high temperature halogen corrosion which will be developed and discussed for the example of oxygen/chlorine environments and which will be named “dynamic” quasi-stability diagram. In part I of the paper, the basis for this new approach to the corrosion resistance assessment of metals under chlorine environments is established using the present understanding described in the literature. A comparison is made between the concept of the conventional stability diagram and the recently developed “static” quasi-stability diagram, where in the latter case the evaporation of the gaseous metal chloride phases is taken into account through the use of a critical metal chloride partial pressure of 10−4 bar, as a criterion distinguishing critical and non-critical corrosion conditions. Concluding from the existing knowledge, the fundamentals for the new improved approach are developed in the form of a “dynamic” quasi-stability diagram. This new type of diagram is based not only on thermodynamic considerations (as for the diagrams existing so far) but also on the products and reactants flow through a gas boundary layer formed on the material surface. As a consequence, in this approach the criterion for corrosion resistance is given in terms of a metal recession rate for dynamic conditions as encountered in most industrial applications. In part II diagrams of the new type will be established for the most common alloying elements, i.e. Fe, Ni, Mo, Cr, Si and Al, and a comparison with experimental data will be performed.

The influence of copper in ash deposits on the corrosion of boiler tube alloys for waste‐to‐energy plants

Abstract: Previous laboratory studies reported in the literature and field experience have revealed the accelerating effect of the heavy metals lead and zinc on the corrosion behaviour of materials used in waste incineration plants. The major problem is that heavy metal containing chloride and sulphate salts usually have relatively low melting points, often below the metal temperature of the boiler surfaces. While the negative influence of lead and zinc is well-known, copper is another heavy metal that can occur in high amounts of up to 2000 mg/kg in refuse-derived fuel, which is the fuel produced by shredding and dehydrating solid municipal waste that is burned in modern waste-to-energy plants. The impact of copper additions on the corrosion behaviour of one iron-based austenitic alloy 1.4952 and three nickel-based alloys 2.4856 (alloy 625), 2.4633 (alloy 602 CA), 2.4605 (alloy 59), which are often used in waste incineration plants was investigated. The results of these studies clearly show the strong corrosive effect of copper content in salt mixtures on the corrosion of steels and nickel-based alloys.

Vanadium-Containing Oil Ash Corrosion of Boilers Under Oxidizing and Syngas Atmospheres

Abstract: Corrosion in oil-fired boilers is accelerated in the presence of vanadium, sodium, and sulfur from low grade fuels. Several iron-based alloys and a nickel-based alloy were studied in order to verify the effect of different Cr and Al contents under conditions typical for the partial oxidation process. Materials performance was analyzed by means of substrate recession rate and metallographic characterization. Samples were exposed to H2S-containing syngas atmosphere in order to simulate boiler operating conditions without ash deposition. The prevailing corrosion mechanism under this reducing atmosphere was sulfidation. In order to simulate boiler conditions with oil ash deposits, samples were immersed in 60 mol% V2O5–40 Na2SO4 salt in the same syngas atmosphere. The prevailing corrosion mechanism in this case was sulfidation under a reducing atmosphere and dissolution of iron or chromium from the substrate. The nickel-based substrate showed the best performance under these experimental conditions. In order to simulate air inlet due to shutdowns, samples were immersed in the same salt during exposure in air. The prevailing corrosion mechanism was still sulfidation in the oxidizing atmosphere accelerated by the presence of vanadate salt. This corrosion mechanism is characterized by the formation of a sulfide/oxide layer adjacent to the metal, the dissolution of oxides in the molten deposit, and their precipitation near the outer surface of the deposit.