Degradation of Type PR and R Thermocouples during Long-term Creep Test

摘要

Controlling of accurate testing temperature is most important for reliable creep test. However, degradation of thermocouples occurs during long-term service for creep test at the elevated temperatures. Thermocouples have been calibrated prior to creep test and thermal electromotive force of those has been measured after service. Magnitude of drift was very small for the thermocouples used at 550℃ and below of that, however, it increased with increasing temperature. Degradation of thermocouples has been sufficiently recovered by repair treatment that is annealing and re-welding. Thermocouples used for the creep test of NRIM/NIMS Creep Data Sheets have been conducted to repair treatment after every creep test regardless of testing time, and a drift of Type R thermocouples has been maintained within ± 4℃ for 100,000h at 650℃.