Non-destructive Testing of Material Amendments in Creep-stressed Power Plant Components - Feasibility Study

Project Number 269

In case of increased stress temperatures, steels show time-related expansion characteristics. Damage to the materials happens under this stress via formation of creep pores and their growing together and forming micro cracks. Quantity and formation of the creep pores, that can be detected experimentally, form a damage measure.

Thus stressed components, however, dispose of another extensive service life potential, that is normally not exhausted. This is due to uncertainties in assessing the material characteristics and the actual operational stress as well as in the calculation methods applied, which do allow only a restricted residual service life prediction.

Within the framework of the VGB Research Programme, research projects are realised which aim at improved calculation of operating parameters, i. e. temperature, component stress as well as material characteristics and thus contribute towards reducing such uncertainties.

In order to be able to exploit the component service life potential, suitable supervision and testing methods must be available to ensure safety and availability.

Actually, irreversible structure changes in the form of creep pores are proved by means of component metallography (replica-technology) within the framework of recurring testing. Other proven, non-destructive testing methods are not available.

In this project it is thus planned to combine several non-destructive procedures. Besides the classic replica technology, these are the multi-frequency eddy current testing (MPA) and the so-called 3MA-process (micro-magnetic multi-parameter microstructure- and tension analysis) developed by IZFP (Institute for non-destructive testing). Furthermore, in order to extend the data basis, comparing tests using also the ultrasound laminography already supported in earlier projects are to be realised.

Investigations are to be realised with operationally stressed and already removed power plant components (also damaged ones) - among them also components from the KOMET650 test plant. Information on creep damage of these components is already available from recurring tests or VGB damage investigations.

This feasibility study primarily aims at determining the meaningfulness of non-destructive test methods in relation to early detection of creep damage in the form of creep pores in heat resistant-steels used in power plant technology. Depending on the results, perhaps a further investigation programme is to be developed.

The investigations planned in this project are to create the conditions to give power plant operators an efficient tool enabling them to realise short-term non-destructive component supervision at reasonable costs.

The project is being co-ordinated by VGB Material Test Laboratory.

The following research institutes are involved:

  • Fraunhofer Gesellschaft - Institut für zerstörungsfreie Prüfung (IZFP) (Institute for non-destructive testing), Saarbrücken
  • Staatliche Materialprüfungsanstalt (MPA) (State materials testing institute), Stuttgart,
  • IST - Ingenieure für Schadensanalyse und Technologietransfer (Engineers for damage analysis and technology transfer), Munich.

The Technical Committee "Materials and Quality Supervision" is supporting the investigations.

The project results are expected in autumn 2007.