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In recent years, the heavy and chemical facilities have been extended its service life through the life assessment and maintenance to reduce the investment because of the economic depression.However, the materials of the facilities operated under high temperature and high pressure is degrading the mechanical properties as increased the service times, so the fracture risk is increased.Therefore, it is necessary to quantitatively evaluate the mechanical properties as well as the nondestructive inspection to decide the operation of the facilities.And, the mechanical properties should be compared to the design values.In general, the non-destructive inspection such as ultrasonic testing, radiography testing, eddy current testing and replication could use the detection and sizing the flaw in the materials.However, the mechanical properties could not be quantitatively evaluated with the general NDT methods.Engineering Critical Assessment (ECA) and Fitness for Purpose for the facilities integrity assessment needs the quantitative information of the flaw and mechanical properties.The instrumented indentation technique(IIT) is a method to quantitatively evaluate the mechanical properties of the materials of the facilities without damage.For the facilities constructed with steel, which is over the design life time and is applied with the repeated load in high temperature and corrosion environment, the mechanical properties snch as yield strength and ultimate tensile strength are evaluated with IIT.And, the operating or not the facilities is decided with the IIT data.