We have investigated the mechanical properties of 15Kh1M1F heat-resistant steel after long-term operation in steam pipelines of steam power plants. The anisotropy of its strength and plasticity characteristics as a result of degradation has been determined. We have established that the number of shutdowns of the process in operation of the steel, orientation of specimens (axial, tangential, and radial), and their location in sections of pipe walls (near their external surface, internal surface, and at the center of the section) influence these parameters. The obtained results enable us to justify the choice of the orientation of specimens and their location in sections of pipes to provide the highest sensitivity of characteristics to a change in the technical state of the steel in operation.