Scanning electron microscope image of a fracture surface for a creep test conducted on aged power plant main steam line weldment. Fracture occurred in the fine-grained heat affected zone of the creep aged metal. Image by Trisha Rasiawan.
Power Plant Materials
Power generating plants operate under highly demanding conditions that include high temperature, high stress, oxidation and corrosion, and complex tribological environments. In its most basic form, plant reliability is critically dependent on the integrity of a broad range of engineering materials (mostly metals) that make up the structures, machines and systems within the plant. Given the anticipated plant life-time, the materials’ integrity is expected to remain within the design performance for periods in excess of 100 000 hours in many instances. Consequently, it is necessary to not only be able to predict the damage that occurs in certain materials as function of exposure to operating conditions, and concomitant loss in design property, but also to be able to accurately characterise the material condition in order to assess the damage levels. Furthermore, the situation is complicated by the fact that repair activities, particularly those involving welding, cause alteration of the existing materials that may disadvantage integrity.
The Eskom fleet presently includes 13 power stations which are coal fired. One of the oldest stations still in operation was built in the 1960s and it has already exceeded its design life-time by some 200%. Advances in technology have allowed engineers to improve stations beyond design performance but there is still considerable opportunity to improve life prediction and extend design performance. Eskom is also expanding its capacity by introducing two new coal-fired stations to their fleet and intend on further expanding the capacity to 75 GW by 2025. While the capital expansion is important, the existing plant needs to continue operating and produce the most energy at the lowest price. A competent research activity that focuses primarily on the high temperature behaviour of engineering materials, with emphasis on materials utilised in power generation (referred to as the Eskom Materials Science Specialisation), is being established within the UCT Centre for Materials Engineering. Research will focus on investigating and understanding the influence of service operating environments on the performance of materials with a view to being able to (a) better predict the life of engineering materials and components in power generating plant, (b) optimize the selection of materials for plant construction, (c) improve manufacturing technologies including welding and (d) improve the reliability in monitoring material and component integrity.
The principal objectives of the Eskom Materials Science Specialisation are to promote knowledge development in materials science which relates to aspects of power generation in the first instance, and secondly to provide a research platform to promote the education of postgraduate candidates in focus areas that will elevate the skills levels of Eskom engineers. There are seven focus areas which can be identified within the materials science specialization requirements outlined by Eskom. These include (a) physical metallurgy and metallography, (b) structural integrity, (c) high temperature behaviour (including creep), (d) environmental degradation (including corrosion), (e) welding metallurgy and processes, (f) materials modelling, and (g) non-destructive evaluation (NDE). The Research Specialisation in materials science will support research projects that address various aspects of these focus areas so that the local knowledge base is expanded with particular relevance to the needs of Eskom and its power generation operations. Where appropriate, the expanded local knowledge base will also be able to provide assistance to the transmission and distribution sectors. The detailed research questions will be formulated in consultation with Eskom experts but it is envisaged that these will be based on topics which include the creep life assessment of metal alloys and welded joints, fracture and fatigue measurement and modelling of boiler tubes and other high temperature components, the creep rupture properties of advanced materials, the effect of welding thermal cycle on service properties, and the use of NDE to assess material integrity and remnant life.