Reliability evaluation of the welded structure is divided by method concentrating on defect and mechanical property. Thermal power plant facilities are operated in high temperature, high pressure and called for safety guarantee. Three factors are constituted for this. The First is PSI(pre-service inspection) and the second is ISI(in-service inspection) and the third is quantitative analysis in safety. Main steam and hot reheat steam pipes in thermal power plant are frequently making a trouble because of unsuitable quality control under construction. So, the suitable construction and the development of life forecast method is urgent matter. Therefore, the continuous indentation technique is interested in effective test method of pipes in power plant facilities. This strong point of the continuous indentation technique is possibility of super-precision measurement, programmed test analysis, nondestructive stiffness evaluation. This study is focused on the possibility of the continuous indentation technique application in main steam and hot reheat steam pipes for stiffness evaluation in thermal power plant facilities.