The results of microstructure and mechanical properties changes of tubes made of Fe-Ni-Cr alloy G-X45NiCrNbTi35-25 after long term operation in methane reformer at elevated temperatures are presented. A method of tube regeneration by using solution heat treatment is proposed. Examinations included metallographic analysis with the use of light microscope (LM), scanning electron microscope (SEM), microanalysis of the chemical composition of precipitates (EDS) and static tensile tests. It was shown that solution heat treatment significantly affects the microstructure of the alloy, restoring the mechanical properties like tensile strength, yield strength and elongation of the tubes close to the values for the delivery condition, over 540 MPa, over 300 MPa and over 12%, respectively. The greatest improvement was observed in elongation, for samples after long-term operation at elevated temperature it was a minimum of 1.1% and after heat treatment 12.1% for the minimum requirement of 8% declared by producer (as cast).