Effect of Rejuvenation Heat Treatment on the Degraded Turbine Blades
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TECHNICAL ARTICLE—PEER-REVIEWED
Effect of Rejuvenation Heat Treatment on the Degraded Turbine Blades Khier Sabri
. Mohamed Ouali Si-Chaib . Mohamed Gaceb
Submitted: 15 March 2020 / in revised form: 29 July 2020 / Accepted: 25 September 2020 ASM International 2020
Abstract This paper presents a novel approach to estimate the extended lifetime of first-stage turbine blades made of directionally solidified GTD-111 nickel-based superalloys. These turbine blades were removed from landbased industrial gas turbines for power generation. In addition, this new way to evaluate the lifetime extension of degraded turbine blades after rejuvenation heat treatment is based on knowledge of newly introduced degradation index (Di) evolution. The rejuvenation heat treatment (RHT) process offers an extension of 36% in blades lifetime. Effect of the RHT on the aged c-c’ microstructures is presented and discussed. Keywords Rejuvenation heat treatment (DS) GTD-111 superalloy Lifetime extension Degradation index c’ (Ni3, Al) precipitates
Introduction Lifetime extension of first-stage gas turbine blades has emerged, as an important issue for industrial operators since each time the blades need to be replaced the turbine must be shutdown [1]. Degraded high-pressure turbine blades may still be in operation, but their residual life was considerably reduced [2]. An analysis is vital to establish inspection periods and to determine the hazard urgency relative to other plants that require being open during the following maintenance intervals [3]. It is a well-known fact
K. Sabri (&) M. O. Si-Chaib M. Gaceb Laboratory of Petroleum Equipment’s Reliability and Materials, Hydrocarbons and Chemistry Faculty, Universite´ M’Hamed Bougara de Boumerde`s, UMBB, Boumerde`s, Algeria e-mail: [email protected]
that rejuvenation heat treatment process is the standard way for the returning to service operation of first-stage turbine blades [4]. The lifetime extension (LTE) is an important economically since it maximizes profits to the operator [5]. Important techniques of critical gas turbine components lifetime assessments are established in the technical literature [6, 7]. Kelekanjeri et al. [8] and Arman et al. [9] suggested that the size coarsening of c’ precipitates is the widely used indicator for accurately estimating the lifetime of creeping turbine blades. Degraded Ni-based superalloys are characterized by c’ particles growth, carbide degeneration, and formation of deleterious phases such as acicular r and platelets g nucleation [10]. The lifetime extension of aged turbine blades was based on rejuvenation heat treatment in order to: revert the c’ precipitates size, reform these particles into the desired shapes, and eliminate deleterious phases formed during service to recover the original microstructure and mechanical properties of turbine blades [11]. The changes in mean size of c’ (Ni3, Al) are very informative to estimate the lifetime extension of rejuvenated GTD-111 blades [12]; therefore, the goal of the restorativ
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