Measurement and compilation of materials degradation data in the COST522 programme

Abstract

Within the European COST522 programme, there are extensive project groupings investigating the degradation of materials, both alloys and coatings, in a wide variety of power plants. Two project groupings are addressing materials degradation in (a) gas turbines and (b) the hot gas paths/heat exchangers of boilers and gasifiers. In both of these broad topics there is a need to generate and compile quantitative information on materials degradation that is appropriate to components operating in systems using new/dirtier fuels, as well as to components operating at higher metal temperatures.

The data generated from research into both of the topics are being compiled into databases. For the boiler/gasifier heat exchanger fireside, the database contains corrosion damage information generated from: (a) a range of plant and pilot plant operations (using biomass, waste and coal fuels), (b) laboratory tests (targeted at particular environments to investigate different specific degradation effects in more detail), and (c) data gathered from the open literature and previous test programmes. For the gas turbine database, data of the performance of base alloys and especially coatings are being included from burner rig and laboratory tests of isothermal oxidation, thermal cycling, hot corrosion performance (as well as data on erosion-oxidation, mechanical and thermo-physical properties). Both databases contain information that precisely specifies the material (coating and substrate, if applicable), as well as accurately describing each test environment and the data produced from each test. The databases are intended to facilitate the comparison of the performance of candidate materials under specific conditions and to enable some of their limitations to be identified, in terms of metal temperature and sensitivity to particular corrosive conditions.

The most valuable corrosion data for inclusion in these databases are those reported in terms of metal loss (or metal loss distribution) and with a well-characterised exposure environment. For the data to be readily incorporated into the databases, it has been necessary to develop and apply standardised methods of data collection, computerised compilation and presentation. The preferred method of gathering corrosion damage data has been by dimensional metrology before and after exposure to obtain a distribution of damage measurements. The structured format of the data in the databases can be used to produce models of materials performance as a function of environmental exposure parameters. This is being investigated for the heat exchanger materials database using both neural network and more conventional empirical modelling.

Keywords:

• degradation of materials
• alloys
• coatings
• COST522 programme