Patterns of Growth of an Internal Annular Crack Under the Influence of Thermal Stresses During Turbine Startup

IF 0.7 4区 材料科学 Q4 MATERIALS SCIENCE, CHARACTERIZATION & TESTING
V. A. Peshko, A. P. Bovsunovskyi
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Abstract

During the operation of a steam turbine, its structural elements are subjected to significant thermal and mechanical loads. The consequence of the long-term effect of such a load is the accumulation of scattered fatigue damage to the material of the structural elements of the steam turbine, which is localized over time in the form of fatigue cracks of various types. Evidence of this is several accidents and catastrophic failures of steam turbines due to significant fatigue damage to the shafting. The localization of damage in turbine rotors is facilitated by stress concentration in the gouges and fillets, as well as damage to the surface layer of the rotors during the thermomechanical treatment stage since all metal processing operations (forging, turning and milling, heat treatment) are accompanied by plastic deformation of the material. One of the reasons for the long-term accumulation of fatigue damage in the structural elements of steam turbines is thermal stresses, which can reach dangerous values during turbine startup operations. In certain parts of the rotors, these stresses are sufficient to cause scattered fatigue damage to the material (the so-called thermoplasticity), especially when starting the turbine from a cold state. In the case of crack initiation, the thermal stresses are all the more sufficient for its further intensive development even when starting the turbine from uncooled and hot states, which are less damaging than starting from the cold state. To study the intensity of crack growth in the turbine rotor due to thermal stresses arising during turbine startup, a computational model based on using a finite element model of the shaft of the K-200-130 steam turbine and fracture mechanics approaches is proposed. Studies based on the proposed computational model have demonstrated the ability to predict the process of crack growth in the rotor due to turbine startup from different thermal states and assess its danger to structural integrity. The initial size of the internal annular crack was determined, which has the potential for further intensive growth under the influence of thermal stresses.

Abstract Image

涡轮机启动期间热应力影响下内部环形裂缝的生长模式
在蒸汽轮机的运行过程中,其结构部件会承受巨大的热负荷和机械负荷。这种载荷长期作用的后果是,蒸汽轮机结构元件的材料会积累分散的疲劳损伤,随着时间的推移,这些损伤会以各种疲劳裂纹的形式局部出现。一些事故和蒸汽轮机的灾难性故障就证明了这一点,这些事故和故障都是由于轴系的严重疲劳损伤造成的。由于所有金属加工操作(锻造、车削和铣削、热处理)都伴随着材料的塑性变形,因此在热机械处理阶段,沟槽和圆角处的应力集中以及转子表层的损坏都会促进汽轮机转子损坏的局部化。热应力是导致汽轮机结构件疲劳损伤长期累积的原因之一,在汽轮机启动运行期间,热应力会达到危险值。在转子的某些部位,这些应力足以对材料造成分散的疲劳损伤(即所谓的热塑性),尤其是当汽轮机从冷态启动时。在裂纹产生的情况下,即使涡轮机从未冷却状态和热状态启动,热应力也足以使裂纹进一步密集发展,而未冷却状态和热状态比从冷状态启动时的破坏性要小。为了研究汽轮机启动过程中产生的热应力导致的汽轮机转子裂纹增长强度,提出了一个基于 K-200-130 汽轮机轴有限元模型和断裂力学方法的计算模型。基于该计算模型的研究表明,该模型能够预测汽轮机启动时不同热状态下转子中裂纹的生长过程,并评估其对结构完整性的危害。确定了内部环形裂缝的初始尺寸,在热应力的影响下,裂缝有可能进一步密集增长。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Strength of Materials
Strength of Materials MATERIALS SCIENCE, CHARACTERIZATION & TESTING-
CiteScore
1.20
自引率
14.30%
发文量
89
审稿时长
6-12 weeks
期刊介绍: Strength of Materials focuses on the strength of materials and structural components subjected to different types of force and thermal loadings, the limiting strength criteria of structures, and the theory of strength of structures. Consideration is given to actual operating conditions, problems of crack resistance and theories of failure, the theory of oscillations of real mechanical systems, and calculations of the stress-strain state of structural components.
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