Research Papers: Gas Turbines: Structures and Dynamics

Mechanical Behavior of Dissimilar Welds for Steam Turbine Rotors With High Application Temperature

[+] Author and Article Information
Stefan Krojer

Materials Testing Institute (MPA),
University of Stuttgart,
Pfaffenwaldring 32,
Stuttgart 70569, Germany
e-mail: stefan.krojer@mpa.uni-stuttgart.de

Eberhard Roos

Materials Testing Institute (MPA),
University of Stuttgart,
Pfaffenwaldring 32,
Stuttgart 70569, Germany
e-mail: eberhard.roos@mpa.uni-stuttgart.de

Andreas Klenk

Materials Testing Institute (MPA),
University of Stuttgart,
Pfaffenwaldring 32,
Stuttgart 70569, Germany
e-mail: andreas.klenk@mpa.uni-stuttgart.de

Shilun Sheng

Siemens AG, Energy Sector,
Rheinstraße 100,
Mülheim an der Ruhr 45478, Germany
e-mail: shilun.sheng@siemens.com

Torsten-Ulf Kern

Siemens AG, Energy Sector,
Rheinstraße 100,
Mülheim an der Ruhr 45478, Germany
e-mail: torsten-ulf.kern@siemens.com

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 23, 2014; final manuscript received July 29, 2014; published online October 7, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(3), 032511 (Oct 07, 2014) (8 pages) Paper No: GTP-14-1429; doi: 10.1115/1.4028435 History: Received July 23, 2014; Revised July 29, 2014

Fossil fired steam power plants of the latest generation require the elevation of steam parameters pressure and temperature to increase efficiency as well as to reduce greenhouse gas emissions. In order to achieve these goals for high temperatures, nickel-base alloys could play an important role for steam turbine applications in the future. Due to technological and economical restrictions, their application in turbine rotors shall be restricted to the most heavily stressed regions. Dissimilar welds offer a known solution to combine nickel-base alloys with ferritic/martensitic steels in this case. Thermal mismatch and differences in high temperature performance of the applied base materials make it very difficult to evaluate the lifetime of such dissimilar welds. Depending on temperature and type of loading, different failure mechanisms can be observed. Further, the type of weld material plays a major role for the service behavior of the weld. Therefore, this paper describes standard creep and fatigue tests which were conducted to identify failure mechanisms and failure locations at the weld zone. To simulate the outcome of the creep tests, a modified Graham-Walles approach is used that also accounts for the different creep behavior of the heat affected zones (HAZs) compared to the base material. For the simulation of the fatigue tests, the model type Chaboche–Nouailhas–Ohno–Wang (CNOW) is used. The results contribute to better knowledge in designing dissimilar welds between nickel-base alloys and martensitic steels under high temperature loading.

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Grahic Jump Location
Fig. 3

Specimen position across the weld: (a) center line = weld metal center position and (b) center line = fusion line at 10Cr side

Grahic Jump Location
Fig. 2

Weld strength factors for similar welds [20,21]

Grahic Jump Location
Fig. 1

Texture of the HAZ including the fusion line, after [19]

Grahic Jump Location
Fig. 4

Comparison of creep rupture behavior

Grahic Jump Location
Fig. 5

Creep rupture deformation behavior at a high stress level: (a) 550 °C and (b) 600 °C

Grahic Jump Location
Fig. 6

Creep rupture deformation behavior at a low stress level: (a) 550 °C and (b) 600 °C

Grahic Jump Location
Fig. 7

Creep rupture deformation behavior of matched welds: (a) high stress level and (b) low stress level

Grahic Jump Location
Fig. 11

Evolution of the maximum LCF stress ratio

Grahic Jump Location
Fig. 8

Creep deformation over time at 550 °C

Grahic Jump Location
Fig. 9

Gauge position for LCF-tests

Grahic Jump Location
Fig. 10

Crack initiation curves for 450 °C and 550 °C with trend line

Grahic Jump Location
Fig. 12

Formation of microcracks in matched welds

Grahic Jump Location
Fig. 13

Formation of microcracks in mismatched welds: (a) fusion line mechanism and (b) mixed mechanism

Grahic Jump Location
Fig. 14

Comparison FE versus experiment, 550 °C

Grahic Jump Location
Fig. 18

Equivalent strain distribution at 550 °C and high strain amplitude of matched welds

Grahic Jump Location
Fig. 15

Deformation response of mismatched creep specimens, 550 °C

Grahic Jump Location
Fig. 16

Stress concentration on the surface at the fusion line of matched creep specimen, no stress concentration for the mismatched specimen

Grahic Jump Location
Fig. 17

Schematic CLCF-preprogram



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