Clarification of the operating behaviour of welded connections between pipes in T91 and E911 X3 CrNiMoN 17-13 at 625 °C under a combined thermal and mechanical load

Project Number 213

A concept for assessing the operating behaviour of mixed pipe connections has been devised as part of a "Mixed Material Weld" project (AVIF 109) funded via the Forschungsvereinigung der Arbeitsgemeinschaft der Eisen und Metallverabeitenden Industrie e.V. (AVIF).

The projects results are published in:

  • R.-U. Husemann, Q. Chen, W. Bendick, J. Heeschen, V. Denner, W. Burget, T. Hollstein, R. Mohrmann, A. Klenk, J. Schemmel, Final report on the research project A109, Mixed material weld; Düsseldorf, Freiburg; March 2001
  • W. Burget, . Hollstein, R. Mohrmann, "Verhalten von Rohrmischverbindung zwischen 9% Chrom-Stählen T91 und E911 und dem Stahl X3 CrNiMo17-13 unter Innendruck und zyklischer Temperaturbelastung: Experiment und numerische Simulation"; VGB Conference "Materials and welding technology in the power plant 1998", Hanover, 14th/15th October 1998
  • W. Burget, T. Hollstein, R. Mohrmann, V. Denner, "Simulation des Verformungsverhaltens und Eigenschaften von Rohrmischverbindungen zwischen den 9% Chromstählen T91 und E911 und dem Stahl X3 CrNiMoN 17-13 unter Innendruck und zyklischer Temperaturbeanspruchung bis 625°C, 2nd lecture event of the AGW and AGH, VDEh, Düsseldorf, 26th November 1999.

This will allow better use to be made of the potential of the new 9%-12% Cr steels for mixed welded connections. The behaviour of welded components is described on the basis of local loads occurring in the mixed connections as the result of combined thermal and mechanical operating loads. The main feature of the new assessment is the transferability of the behaviour of the mixed connections from single axis loads, as in the case of standard material qualification and testing, to multi-axis and combined load states relevant for components, which are characteristic for the operation of mixed pipe connections in installations, for example.

The aim of the project is to verify this evaluation concept for the long-term behaviour of welded mixed pipe connections by coordinated component tests and digital simulation calculations. This will be achieved on the basis of existing results of the AVIF project and through the following investigation stages for mixed pipe connections between 9% Cr steel T91 (and E911) and the austentic steel 1.4910:

  • incorporating the long-term single axis creep properties of the HAZ areas of T91 (coarse particle, fine particle, inter-critical HAZ) in existing material models to describe the complex load
  • qualification of mixed pipe connections optimised beforehand in the component test up to a total test time of 5000 hours
  • verification of the concept for predicting the deformation and failure behaviour on the basis of FE calculations for the above-mentioned component tests
  • application of the life prediction concept for available component tests on mixed pipe connections.

The project will be conducted by the Fraunhofer Institut für Werkstoffmechanik, Freiburg, under the leadership of Dr. Thomas Hollstein. Helmut Salomon, FDBR, and Dr. Thomas Hollstein will coordinate the project. The VGB Technical Committee "Materials and Quality Supervision" will provide technical support for the project.