焦炉用铠装热电偶失效原因分析

Failure analysis of sheathed thermocouple used in coke oven

国内某钢铁厂焦炉测温用铠装热电偶,安装后使用5天便发生了失效故障,无法显示温度读数。为探究其热电偶失效原因,对其铠装热电偶先后进行了低倍下的宏观形貌观察、扫描断口分析、显微组织分析和电子探针成分分析等。结果表明:该热电偶失效的原因是镍铬端发生了择优氧化。改进措施及建议:使用时合理选择适合型号的热电偶,排除K型热电偶在加工时表面的氧化皮以及还原性介质的介入和采用较小的长径比。

A sheathed thermocouple used in a coke oven in a domestic steel plant became invalid after installed,and used for 5 days,which could not show the temperature readings any more. The failure reasons of the thermocouple were investigated by means of macroscopic appearance observation,fracture analysis by the scanning electron microscope( SEM),microstructure analysis by optical microscope( OM),composition analysis by electro probe microanalyzer( EPMA),respectively. The results show that the failure of the thermocouple is mainly attributed to the preferential oxidation of the nickel-chromium end. Improvement measures and suggestions: select the right type of thermocouple reasonably when using,eliminate the oxide skin on the surface of K-type thermocouple and the intervention of reducing medium during processing,and adopt a smaller length diameter ratio.