High temperature In-situ Monitoring of Power Station Steels using Electromagnetic Sensors - POWEREMS

目前尚无技术可用于监测在役(即高温下)的电站钢部件的微观结构状况。这个问题将变得更加严重，因为燃煤发电站正在发展，以在更高的压力和温度下运行，以提供更高的效率；超临界发电站可以产生45%到50%的输出效率，而亚临界发电站的效率为30%到35%。现在可以在620摄氏度下运行，计划到2014年将温度进一步提高到700摄氏度。超临界发电站向环境中排放的二氧化碳也减少了25%(效率每提高1%，二氧化碳、氮氧化物和硫氧化物等排放量就会下降2%)。目前，电站部件的状况是在停机期间进行监测的，此时绝缘层被移除，并从部件表面复制。对这些复制品进行检查，以确定微观结构状态(退化程度，例如通过碳化物数量的变化)以及是否已开始蠕变空化。当达到预计使用寿命结束或检测到严重气蚀时，部件将被从服务中移除并更换。然而，由于只能在预定的停机期内检查部件状况，因此经常过早更换部件。如果一个部件发生故障，经济影响是严重的(非计划关闭估计每个发电站每天的损失约为150万英镑)，并可能对生命和环境造成重大风险。拟议的项目是研究多频电磁(EM)传感器系统的潜力，该系统用于监测发电用钢(例如锅炉板和管)由于高温暴露和蠕变而产生的微观结构变化，以便在维护期间进行在役监测和评估。这项工作将涉及开发长期在高温下使用的传感器系统，以及与钢的微观结构变化相关的传感器信号的分析和建模。

There are currently no techniques available to monitor the microstructural condition of power station steel components in-service (i.e. at elevated temperatures). This problem will become more acute as coal-fuelled power stations are being developed to operate at higher pressures and temperatures to provide greater efficiency; supercritical power stations could produce output efficiencies of 45 to 50 %, compared to subcritical power stations with efficiencies of 30 to 35 %. Operation at 620 deg C is now possible, with further temperature increases to 700 deg C planned by the year 2014. Supercritical power stations also emit up to 25 % less carbon dioxide into the environment (a one percent increase in efficiency gives a two percent drop in emissions such as carbon dioxide, and nitrogen and sulphur oxides). Currently the condition of power station components is monitored during shut down periods, when insulating lagging layers are removed and replicas from the component surface are made. These replicas are examined to determine the microstructural state (degree of degradation, e.g. through carbide population changes) and whether creep cavitation has initiated. Components are removed from service and replaced when end of predicted service life is reached or significant cavitation is detected. However, as the component condition can only be checked during a scheduled shut down period, sections are often replaced prematurely. If failure of a component occurs the economic impact is severe (an unplanned shutdown is estimated to cost approximately 1.5M per day per power station) and there is potentially significant risk to life and the environment. The proposed project is to investigate the potential of a multi-frequency electromagnetic (EM) sensor system for monitoring microstructural changes in power generation steels (e.g. boiler plate and pipe) due to high temperature exposure and creep for both in-service monitoring and evaluation during maintenance periods. The work will involve development of a sensor system for long term use at elevated temperatures, and analysis and modelling of sensor signals relative to microstructural changes in the steels.