CF-8M铸造不锈钢热老化的无损检测和评估方法研究

Nondestructive Testing and Evaluation Method of Thermal Aging of CF-8M Cast Stainless Steel

核电站主管道铸造不锈钢在280~325℃下长期运行服役过程中存在热老化脆化问题,韧性会大幅下降,为检测和评估主管道材料的热老化程度,通过对核级CF-8M静态铸造不锈钢主管道材料在400℃下热老化10000 h的样品进行了热电势测量,研究了不同热老化阶段的力学性能(冲击能)和热电势与老化时间的关系,获得了热老化影响因素归一化后的参数与力学性能(冲击能)和热电势的对应关系式。结果表明,在热老化初始阶段冲击能下降较快,达到8000 h后冲击能下降趋势已趋于平缓。在试验周期内,随着对数老化时间的增加,热电势呈线性增加;随着热电势的增加,冲击能开始下降较快,后期下降趋势变缓,逐渐趋于饱和,冲击能随热电势变化的形式和冲击能随热老化时间变化的形式相似。对热老化影响因素进行归一化后的参数值与热电势呈线性关系,基于该关系式可利用热电势检测技术评估服役部件热老化后的性能下降程度。

The main pipe of PWR is the key component of the steam supply system of nuclear power plant,and it is also an important part of the reactor coolant pressure boundary.The main pipe of the coolant system of light water reactor is made of cast stainless steel parts,which has high material strength,high toughness and good corrosion resistance.However,there is thermal aging embrittlement during long-term operation at 280-325℃,resulting in the increase of hardness and tensile strength of stainless steel,and the significant decrease of impact energy and toughness.Therefore,the safety margin of the main pipeline should be analyzed and evaluated to ensure the safe and reliable operation,which is an important link in the aging management of the main pipeline.Especially when the nuclear power unit in service is ready to prolong its life,the requirements of thermal aging detection and evaluation of main pipeline are put forward.Therefore,it is necessary to use nondestructive method to detect the thermal aging of the main pipeline in service and evaluate the thermal aging state.The thermoelectric power of nuclear grade CF-8M static cast stainless steel main pipe material was measured after thermal aging test at 400℃for 10000 h.The relationship of mechanical properties(impact energy)and thermoelectric power with aging parameters after different thermal aging time was investigated,and the corresponding relationship between normalized parameters of thermal aging influencing factors and mechanical properties,thermoelectric power value was obtained.The experimental results show that the impact energy decreases rapidly in the initial stage,and the decreasing trend of impact energy tends to be gentle after thermal aging to 8000 h.During the experiment,the thermoelectric power increases linearly with the increase of logarithmic aging time.With the increase of thermoelectric power,the impact energy begins to decrease rapidly,and then decreases slowly and gradually tends to saturation.The variation of impact energy with thermoelectric power is similar to that of impact energy with thermal aging time.Based on the linear relationship between the normalized parameters and thermoelectric power,the degree of performance degradation after thermal aging for service parts can be evaluated by the thermoelectric power.This experimental study provides a test basis for thermoelectric power detection and thermal aging evaluation of main pipe components on-site.