Testability of Thick-walled Components Made from Nickel-based Alloys and Welded Connections Using Non-destructive Testing Methods (COORETEC, TD-1)

Project Number 296

The application of new technologies to increasing efficiency in high-performance power plants primarily consists in significantly increasing the steam parameters for pressure and temperature. The materials previously used are only conditionally suitable under such loading conditions, and nickel-based alloys must thus increasing be used.

In addition to the improved characteristics of the materials themselves, the adequate detectability of defects in thick-walled components made from nickel-based alloys is of critical significance for their manufacture, safe commissioning and reliable operation.

In order to guarantee this, work on the examination and development of suitable non-destructive ultrasound testing methods is being carried out in the COORETEC project TD-1 "Testability of thick-walled components made from nickel-based alloys and welded connections using non-destructive testing methods". The creation of a scientific database of process limits should also allow reliable decisions to be made regarding the applicability, reliability and confidence limits both of the conventional techniques and of the improved testing techniques in their application to welded components made from nickel-based alloys.

According to our current understanding, the same problems are to be expected in ultrasonic testing as for austenitic weld seams; probably in more severe form when inspecting wall thicknesses of 80 - 100 mm. The main problem lies in the acoustic anisotropy of the weld seams, which often interferes with the way in which the ultrasound waves spread, thus making them unpredictable. Backscattering, reflections, refractions and wave-splitting thus not only occur at the grain boundaries, but also in the area of the fusion line.

The inspection and analysis techniques developed for austenitic materials and welded connections (e. g. antenna arrays, SAFT) should therefore be tested and developed within the framework of the project for use on these thick-walled nickel-based alloys and their welded connections.

The project is being carried out in the period from 1 September 2006 to 31 October 2009 by the Fraunhofer Institute for Non-destructive Testing (Fraunhofer Institut für zerstörungsfreie Prüfverfahren - IZFP), the Federal Institute for Materials Research and Testing (Bundesanstalt für Materialforschung und -prüfung - BAM) and the University of Stuttgart Materials Testing Institute (Materialprüfungsanstalt Universität Stuttgart - MPA).

The research institutes are jointly examining existing processes with the aid of defined test objects. The IZFP and BAM are working on the development and improvement of the processes and are carrying out the examinations by determining the process limits. The MPA Stuttgart is coordinating the provision and distribution of test objects, and is implementing the results in fault tolerance and evaluation by fracture mechanics methods, in addition to verification of the non-destructive testing results.

The participating manufacturing companies,

  • ALSTOM Power Boiler GmbH (Stuttgart),
  • ALSTOM Power Generation AG (Mannheim),
  • Hitachi-Power Europe GmbH,
  • Essener-Hochdruck-Rohrleitungsbau GmbH,
  • Siemens Aktiengesellschaft,

supply the industrial know-how regarding the tests that have to be carried out during manufacturing and acceptance of components, and are participating in the manufacture of the test objects.

The participating power plant operators,

  • E.ON Energie AG,
  • EnBW Kraftwerke AG,
  • Grosskraftwerk Mannheim AG,
  • RWE Power AG,
  • STEAG Aktiengesellschaft,

define the requirements, contribute their practical experience in the use of non-destructive testing over many years of operation and are participating in the examination of the processes.

The partners from industry are accompanying the project in a steering committee coordinated by VGB, and are evaluating the results established.

Within the framework of the COORETEC research programme, 50 % of the research project is financed with funds from the German Ministry of Economics (sponsorship ID numbers 0327705Q, 0327705R and 0327705S); 80 % of the industrial funding comes from the participating power plant operators and 20 % comes from the participating manufacturers.