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Licensed Unlicensed Requires Authentication Published by De Gruyter February 19, 2021

Gamma Prime Solutioning Tests of Alloy 247 Specimens

Lösungsglühversuche an Proben aus Alloy 247
  • A. Neidel EMAIL logo , B. Fischer

    Boromir Fischercompleted a training as State Certified Technical Assistant for Metallography and Physical Material Analysis at Lette-Verein in Berlin. He has worked in the metallographic laboratory of the Siemens Gas Turbine Plant (Siemens-Gasturbinenwerk) Berlin for more than a decade. The key areas of his work are failure analysis and microstructural examinations using the field emission scanning electron microscope.

    and M. Giller

    Madeleine Gillerapprenticeship as a materials testing technician at the welding institute SLV Berlin-Brandenburg. After that, she studied materials science at the Berlin Institute of Technology. She graduated with a masters degree in materials science in 2012. Since November 2012 employment as engineer at the Metallography Laboratory of the Siemens Gas Turbine Works in Berlin. She has been appointed laboratory manager within the Berlin Testing Center of the Large Gas Turbine Engineering Group in 2014. Her main fields of expertise comprise failure analysis and microstructural investigations using the field emission scanning electron microscope.

From the journal Practical Metallography

Abstract

Strictly speaking, this contribution is not about a case study in failure analysis. However, the investigation described herein was inspired by a failure case. A heavyduty gas turbine engine used in a power and desalination plant in the Middle East experienced creep damage and cracking in some of its row 4 turbine blades after only some 15,000 operating hours. Microstructural alterations detrimental to the creep strength of the alloy were determined to be the metallurgical root cause of the failure. It was believed that said microstructural alterations were brought about by unusual transient operating conditions in engine service. Heat treatment tests were ordered to verify or disprove this hypothesis. It was established that the peculiar gamma prime morphology found in the failed blades can be produced by very high solutioning temperatures and subsequent rapid cooling. Such conditions in engine service are conceivable if sufficient unburnt fuel enters the turbine and ignites downstream of the combustion chamber (high temperature), and if water used in fuel line purging is injected into the turbine section immediately thereafter (rapid cooling). Solutioning above 1240 °C, followed by a water quench, produced said mono-modal fine γ' morphology.

Kurzfassung

Streng genommen geht es in diesem Beitrag nicht um eine Fallstudie auf dem Gebiet der Schadensfallanalyse. Die im Folgenden beschriebene Untersuchung wurde jedoch von einem Schadensfall angeregt. Bei einer Großgasturbine, die in einer Kraftwerks- und Entsalzungsanlage im Mittleren Osten eingesetzt ist, wurden nach nur etwa 15.000 Betriebsstunden Kriechschäden und Risse in einigen Turbinenschaufeln der 4. Reihe entdeckt. Veränderungen der Mikrostruktur, die sich nachteilig auf die Kriechbeständigkeit der Legierung auswirken, wurden als metallurgische Schadensursache ermittelt. Es ist davon auszugehen, dass die beschriebenen Veränderungen der Mikrostruktur durch ungewöhnliche transiente Betriebszustände im Turbinenbetrieb hervorgerufen wurden. Um diese Annahme zu bestätigen bzw. zu widerlegen, wurden Wärmebehandlungsversuche in Auftrag gegeben. Es konnte nachgewiesen werden, dass die spezielle γ'-Morphologie, wie sie in den beschädigten Schaufeln beobachtet wurde, durch sehr hohe Lösungsglühtemperaturen und anschließendes schnelles Abkühlen hervorgerufen werden kann. Solche Bedingungen sind im Turbinenbetrieb dann vorstellbar, wenn eine ausreichend große Menge an unverbranntem Brennstoff in die Turbine gelangt und sich hinter der Brennkammer entzündet (hohe Temperatur) und wenn Wasser, das zum Spülen der Brennstoffleitung verwendet wird, unmittelbar danach in diesen Turbinenabschnitt gelangt (schnelles Abkühlen). Lösungsglühen bei über 1240 °C mit anschließender Wasserabschreckung führt zu der beschriebenen monomodalen feinen γ'-Morphologie.

About the authors

B. Fischer

Boromir Fischercompleted a training as State Certified Technical Assistant for Metallography and Physical Material Analysis at Lette-Verein in Berlin. He has worked in the metallographic laboratory of the Siemens Gas Turbine Plant (Siemens-Gasturbinenwerk) Berlin for more than a decade. The key areas of his work are failure analysis and microstructural examinations using the field emission scanning electron microscope.

M. Giller

Madeleine Gillerapprenticeship as a materials testing technician at the welding institute SLV Berlin-Brandenburg. After that, she studied materials science at the Berlin Institute of Technology. She graduated with a masters degree in materials science in 2012. Since November 2012 employment as engineer at the Metallography Laboratory of the Siemens Gas Turbine Works in Berlin. She has been appointed laboratory manager within the Berlin Testing Center of the Large Gas Turbine Engineering Group in 2014. Her main fields of expertise comprise failure analysis and microstructural investigations using the field emission scanning electron microscope.

References / Literatur

[1] Neidel, A.; Giller, M.; Riesenbeck, S.; Wöhl, E.: Ageing Tests of Alloy 617 to Simulate Service Embrittlement. Pract. Metallogr. 55 (2018) 12, S. 826 – 841 DOI: 10.3139/147.11050310.3139/147.110503Search in Google Scholar

[2] Neidel, A.; Matijasevic-Lux, B.; Riesenbeck, S.; Ullrich, T.; Völker, J.; Wallich, S.: Schäden an Brennerkomponenten von Heavy duty-Gasturbinen. Prakt. Metallogr. 47 (2010) 3, S. 135 – 149 DOI: 10.3139/147.11005610.3139/147.110056Search in Google Scholar

[3] Neidel, A.; Fischer, B.; Giller, M.: Internal report BLN MT/2019/0385. Berlin, August 1, 2019Search in Google Scholar

[4] Nadeer, A.: Internal fact finding report 2018 – 015, January 1, 2018.Search in Google Scholar

Received: 2020-02-28
Accepted: 2020-07-01
Published Online: 2021-02-19

© 2021 Walter de Gruyter GmbH, Berlin/Boston

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