During the operating of metal constructions, including pipelines, as a result of exposure to metal various external factors, in it can occur different changes. These changes can have a significant impact on the mechanical characteristics of the metal and, as a result, on the operational reliability of the constructions. The article presents a new method of non-destructive assessment of modification of metal technical condition. The essence of the method consists in obtaining sample values of microhardness of the metal (about 100 values) in the investigated area of construction and comparing it with a sample of the microhardness values of the same metal, but in the initial state. Due to the studies, it have been established the criterias, according to which the comparison of samples of microhardness values, allows qualitative evaluation of the flow in the metal different processes such as an increase in the dislocation density, the formation of microcracks and age-hardening. In case of increasing the dislocation density in the metal, in the sample of the microhardness values appears the array of higher values of microhardness, in comparison to the original sample. In case of forming microcracks in metal, when hit by the indenter in it's, in the samples of microhardness values will be detected the failures of single values. The age-hardening of the metal leads to appearance of the array of microhardness values, lower than the minimum value of microhardness in the source samples. The established criterias were obtained on different types of steels and confirmed by electron-microscopic researches, which allowed to conclude about the universality and validity of the developed method.