Issue 30

D. Nappini et alii, Frattura ed Integrità Strutturale, 30 (2014) 394-402; DOI: 10.3221/IGF-ESIS.30.47 394 Focussed on: Fracture and Structural Integrity related Issues Evaluation of the material’s damage in gas turbine rotors by instrumented spherical indentation D. Nappini, G. Zonfrillo Department of Industrial Engineering, University of Florence, Via S.Marta 3, Florence, Italy duccio.nappini@unifi.it, giovanni.zonfrillo@unifi.it F. Mastromatteo, I. Giovannetti GE Oil&Gas, Florence, Italy francesco.mastromatteo@ge.com , iacopo.giovannetti@ge.com A BSTRACT . Experimental indentations are carried out on items of two different materials, taken in several location of various components from high pressure gas turbine rotor which have seen an extensive service. The components object of investigation consisted in 1 st and 2 nd high pressure turbine wheels made in nickel-base superalloy (Inconel 718), the spacer ring (Inconel 718) and the compressor shaft made in CrMoV low alloy steel (ASTM A471 type10). Aim of the work is to set up the capability of the instrumented spherical indentation testing system to evaluate variations in the material properties due to damage, resulting from temperature field and stresses acting on components during service. To perform this task load-indentation depth curves will be acquired in various zones of the above mentioned components. The analysis of the results has allowed to identify an energy parameter which shows a linear evolution with the mean temperature acting on the components. K EYWORDS . Instrumented indentation; Depth-sensing indentation; Material characterization. I NTRODUCTION eavy-duty and aircraft-derivative gas turbines rotors for power generation and industrial applications are among the most critical and highly stressed components of the plants and they are expected to reliably operate for a period which may be in excess of thirty years. Over the turbine’s life the structural integrity of rotor materials naturally declines when subjected to the harsh conditions of gas turbine operation; high temperatures exposure, mechanical stress and startup/shutdown cycles result in the initiation and growth of flaws, which can eventually compromise the machine’s safety and integrity. Remaining life assessment methodologies employ a combination of traditional and high-tech non-destructive tools and methods to evaluate the mechanical integrity of rotors; therefore, they can be used to confirm the safety of continued operation or to recommend necessary restoration [1-4]. The measure of material’s mechanical properties are a fundamental task in safety design and lifetime assessment of industrial components and among the in-field inspection and real-time monitoring non-destructive methods indentation- H