During the exploitation of the atomic power stations the tubing metal is exposed to the influence of temperatures in the range of 290-320С. It can lead to thermal ageing and to the decrease of the embrittlement resistance. The critical embrittlement temperature is the main value which is needed to calculate the embrittlement resistance of materials. The metal properties degradation is taking into account by introduction of the shift of critical embrittlement temperature. The presented data ensure the prognosis of tube steels properties and shift of the critical embrittlement temperature for 60 years resource.