Special features of the structure and properties of the metal of centrifugally cast large-diameter tubes from steel 15Kh1M1F used in hot reheat steam conduits of high-power generating units are discussed. The metal of the tubes in the initial state is shown to possess structural heterogeneity primarily represented by segregation bands. The segregation bands are responsible for scattering of the mechanical properties and a 5 – 10% decrease in the long-term strength in the initial condition. The decline of the long-term strength intensifies with the propagation of the segregation over the cross section of the tubes. The segregation lowers the stability of the structure and properties of the tubes in operation at a high level of long-term plasticity. By reducing the degree of segregation in centrifugally cast tubes the time of their operation in steam conduits can be increased to 200,000 h.