Fatigue crack growth resistance of the 12Kh1MF steel from different zones of steam pipeline bends of TPP after long term operation [in Ukrainian].
Journal Title: Вісник Тернопільського національного технічного університету - Year 2015, Vol 80, Issue 4
Abstract
Hard temperature-power operating condition of the steam pipeline (vapor pressure up to 14 MPa, temperature – up to 565 oC and a large number of shutdowns of the technological process), and long- term influence of an aggressive hydrogenating environment on stressed metal promote degradation of its structure and worsening of the mechanical properties, which ensured their workability at the beginning of operation. Therefore, the diagnostics of the technical state of steam pipeline bends directed on providing the reliability of their operation does not lose relevance to the power system of Ukraine with critically wear of equipment. The 12Kh1M1F steel from different zones of pipe bend from main steam pipelines after ~13104 h operation was investigated. During bend manufacturing the deformation of metal from its different zones (stretched, neutral and compressed) is not the same. As a result the properties of degraded metal from these zones are different too. The nominal and effective fatigue crack growth diagrams of the metal of stretched, neutral and compressed zones and straight pipe were received. Thresholds fatigue crack growth resistances were defined too. It is shown that the effective threshold fatigue crack growth resistance of metal with compressed zone is lower compared with other zones. High sensitivity of local fracture mechanics parameters to the metal degradation and their ambiguous changes in various zones at the same service duration and conditions were proved. It was shown that metal from compressed zone was the most degraded because its fatigue threshold levels were the least. It was explained by an appearance of dissipated intergranular damages in metal under the influence of thermal fatigue. Such intergranular elements on the fracture surface facilitate the fatigue crack growth and cause the strongest crack closure effect under fatigue test of degraded metal from compressed zone of bend.
Authors and Affiliations
Lesya Svirska, Halyna Krechkovska, Oleksandra Student
Keywords
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