Patent Number: 
Section: claims

1. A method of extending a life expectancy of a high-temperature piping, comprising:when it is determined that a continued stationary use cannot be performed by a remaining life expectancy evaluation of a creep rupture of a welded portion of the high-temperature piping,peeling off a part of a heat insulation material from an outer surface of the high-temperature piping, which covers a location having a high creep rupture risk in the high-temperature piping, to form an exposed portion of the high-temperature piping; andlowering an outer surface temperature of the high-temperature piping locally to extend the life expectancy of the location having the high creep rupture risk,wherein a width of the exposed portion of the heat insulation material is twice or more a distance from an end portion of the exposed portion to a portion where a compressive stress is asymptotical to 0 after a change in stress between a tensile stress and the compressive stress occurring in the high-temperature piping due to the removal of the heat insulation material is made from the tensile stress to the compressive stress, andthe distance at which the compressive stress after a change in stress is made from the tensile stress to the compressive stress is asymptotical to 0 is based on the following formula (1),βx=5  (1)β is expressed by the following formula (2),                    β        =                                            3              ⁢                              (                                  1                  -                                      v                    2                                                  )                                                                    a                2                            ⁢                              h                2                                              4                                    (        2        )            here, x is a distance from the end portion of the exposed portion, ν is a Poisson's ratio, and symbol a is an average radius of the piping, and symbol h is a plate thickness of the piping. 2. The method of extending the life expectancy of the high-temperature piping according to claim 1, wherein the outer surface of the high-temperature piping, from which the heat insulation material has been removed, is cooled. 3. The method of extending the life expectancy of the high-temperature piping according to claim 2, wherein the cooling is cooling by air or cooling by cooling water. 4. The method of extending the life expectancy of the high-temperature piping according to claim 1, wherein a heat dissipating member is installed on the outer surface of the high-temperature piping from which the heat insulation material has been removed. 5. The method of extending the life expectancy of the high-temperature piping according to claim 1, wherein the temperature of the outer surface of the high-temperature piping, from which the heat insulation material has been removed, is measured to determine that the cooling capacity is appropriate. 6. The method of extending the life expectancy of the high-temperature piping according to claim 5, wherein, when the cooling capacity is not appropriate, the cooling capacity is changed to be appropriate. 7. A life expectancy extension structure of a high-temperature piping,in which a width of an exposed portion of the high temperature piping where a part of a heat insulation material that covers a location having a high creep rupture risk in the high-temperature piping is peeled off is twice or more a distance from an end portion of the exposed portion to a portion where a compressive stress is asymptotical to 0 after a change in stress between a tensile stress and the compressive stress occurring in the high-temperature piping due to the removal of the heat insulation material is made from the tensile stress to the compressive stress, andthe distance at which the compressive stress after a change in stress is made from the tensile stress to the compressive stress is asymptotical to 0 is based on the following formula (1),βx=5  (1)β is expressed by the following formula (2),                    β        =                                            3              ⁢                              (                                  1                  -                                      v                    2                                                  )                                                                    a                2                            ⁢                              h                2                                              4                                    (        2        )            here, x is a distance from the end portion of the exposed portion, ν is a Poisson's ratio, and symbol a is an average radius of the piping, and symbol h is a plate thickness of the piping. 8. The life expectancy extension structure of the high-temperature piping according to claim 7, comprising:a cooling unit that cools a surface of the exposed portion of the high temperature piping from which the heat insulation material has been removed. 9. The life expectancy extension structure of the high-temperature piping according to claim 8, wherein the cooling unit is an air-cooling unit by air or a water-cooling unit by cooling water. 10. The life expectancy extension structure of the high-temperature piping according to claim 7, wherein a heat dissipating member is installed on the surface of the exposed portion of the high temperature piping from which the heat insulation material has been removed.