低硬度P91管件的安全性评价及寿命预测

为确保热力系统管材与设备使用安全,对不同硬度的P91试样在570 ℃下进行了持久断裂试验,并采用对数函数对试验结果进行了拟合,用以对P91管材进行安全性评价及寿命预测,可避免采用等温线外推法导致的持久强度过估。研究结果表明,低硬度P91管件,570 ℃下1×10⁵ h持久强度随硬度下降呈下降趋势,硬度低于165 HBW,P91钢持久强度下降至许用应力以下,不能保证其长期安全运行;低参数运行的P91管件（再热蒸汽管道及亚临界参数管道）强度裕量较高,允许硬度有适当降低;而在570 ℃左右运行的主蒸汽管道,尤其是未作增厚设计的弯头,强度裕量低,必须进行安全性评价和寿命预测。

Safety Evaluation and Lifespan Prediction of Low Hardness P91 Pipes

In order to ensure the safety of the piping and equipment used in the thermal system, the creep rupture test is carried out at 570 ℃ on the P91 specimens with different hardness. The test results are fitted by the logarithmic functionfor safety evaluation and lifespan prediction of the P91 pipe, such that the overestimation on long-term creep rupture caused by isothermal extrapolation method can be avoided. The study results show that for low hardness P91 pipe fittings, the creep rupture of 570 ℃/1×10⁵ h tends to drop with the decrease of hardness. Especially when the hardness goes down below 165 HBW, the creep rupture strength of P91 steel will decrease below the material allowable stress, which means its long-term safe operation cannot be ensured. The P91 pipes in operation with low parameter settings have a larger strength margin, and its hardness is allowed to be lower to some extents. However, for the main steam pipeline operated at 570 ℃, especially without thickening designed bend, the strength margin is very low. Therefore, the safety evaluation and lifespan prediction is compulsory.