New laboratory for high temperature corrosion at the Duisburg location

The commissioning of two experimental  set-ups for the simulation of high temperature corrosion processes in power plants has extended the expertise of SZMF Research and Development in Duisburg by a new field of competence in the area of heat resistant steel products.

 

Currently, state-of-the-art, coal-fired high-performance power plants operate with steam parameters of 600°C und 290 bar at efficiencies of 47 %. In order to be able to achieve an efficiency of 50 % and higher, it is mandatory to increase the steam temperature to approximately 700°C and operating pressure to approximately 350 bar in future power plants. In addition, the application of new technologies such as the Oxyfuel combustion process generates new conditions. The impact of such conditions on the material  lifetime  are more or less unknown. Since the boiler components (superheater tubes, membrane walls, and live steam lines) must be capable to withstand these new conditions, power plant operators, boilermakers and tube manufacturers are strongly promoting the development of resistant materials for the new power plant concepts.

 

The aspect of creep rupture strength played a primary role in previous approaches to the development of materials for high-performance power plants, whereas oxidation resistance in steam and corrosion on the flue gas side  were not considered to be significant  becausee of the relatively low metal temperatures. However, due to the planned operating temperatures and modified combustion atmospheres for the power plants of the next generation,  oxidation in steam at the inner surface of the tubes and,  in contact with the  flue gas will play a  more and more important role.

 

Generally, at temperatures above 600°C the chemical reactions of the inner tube surface with hot steam will increase. These reactions lead to the formation of thick oxide layers and

evaporation of volatile corrosion products. Both the wall thickness losses and restricted thermal transfer capabilities are not acceptable. The development of corrosion on flue gas side at temperatures in the range of 700°C propagated particularly by sulfur components in the flue gas (SO₂) and ash deposits (sulfates). There is an urgent need to examine and assess the aspect of high temperature corrosion and creep rupture strength at an equal level of importance right from the start of material development.

The thermal technology laboratory in the  department  of material technology can now rely on two test stands for the examination of the material response under steam and flue gas corrosion conditions. For this purpose, two horizontal furnaces were installed to cover the temperature range from 400 °C to 900 °C. For examinations of high temperature corrosion under fuel gas conditions, the furnace is charged at a constant flow rate with a corrosive gas mixture that is especially prepared for this test. The variability of the gas components facilitates selection of different gas compositions and optimization of a practical material environment. It is also possible to perform tests at simulated ash deposit conditions. For examinations of steam corrosion, the furnace is charged with saturated steam at a constant flow rate. Each test stand facilitates up to 18 simultaneous high temperature corrosion tests with a runtime from 1 h to more than 10.000 h. This enables the examination of the entire material spectrum that comprises conventional martensitic chrome steels to sophisticated nickel base materials.

Appropriate experimental control and post examination processes enable the determination of the time-dependent corrosion behavior (e.g. metal losses) at given operating conditions (atmosphere and temperature). In these processes, it is also possible to ascertain the effects of specific alloying elements on corrosion.

 

With the new field of competence, SZMF has responded to growing demands on the development of new high-performance materials for the next generation of power plants. SZMF is thereby meeting the currently rising demands for a systematic, experimental analysis of the corrosion behaviour of high temperatur materials in steam and flue gas.