基于有限元的溶氧蒸汽环境TP347H管氧化膜剥落特性分析

Investigating the Role of Oxygenated Treatment on Oxide Exfoliation in TP34H Alloy Tube Based on Finite Element Method

超(超)临界火电机组广泛采用给水加氧处理方式,这使得蒸汽通道合金管氧化膜发生物理和化学变化,加剧氧化膜在停炉过程中大规模剥落,影响机组安全运行。该文针对停炉过程,建立包含交界面缺陷的氧化膜热力耦合有限元模型,量化分析氧化膜外表面Fe2O3和内外层交界面缺陷对TP347H合金氧化膜剥落的影响。研究结果表明,Fe2O3对氧化膜应力没有促进作用,反而会降低氧化膜应力。Fe2O3厚度对缺陷区能量释放率的影响也较少,不是加剧氧化膜剥落的主要因素。内外层交界面缺陷对氧化膜剥落的影响远高于Fe2O3,氧化膜交界面缺陷尺寸越大,越容易导致氧化膜剥落。现有理论研究仍难以量化分析缺陷生长,在实际工程中,可利用蒸汽中铬酸根离子量间接反映氧化膜缺陷。

The supercritical units adopt the oxygenated treatment(OT) widely, which could cause physical and chemical changes on the oxide scale formed on the inner surface of tubes. This behavior leads to the oxide exfoliation in the shutdown process and affect the safe operation of the power plant. This paper dealt with the shutdown process, and the finite element model containing interface defects was developed to compare the influence of Fe2O3 thickness and interface defect size on the oxide exfoliation. The results show that Fe2O3 could not promote the oxide stress, on the contrary, it would reduce the oxide stress. The Fe2O3 thickness has seldom effect on the energy release rate of the defect area, which is difficult to promote the oxide exfoliation. The interface defect between the inner and outer layers has greater effect on the oxide exfoliation than the Fe2O3 thickness. The larger the oxide defect, the more likely it will cause the oxide exfoliation. It is still difficult to quantify defect growth in existing studies. In the engineering application, the oxide defects can be indirectly reflected by the amount of chromate ions in the steam.