Method of extending life expectancy of high-temperature piping and life expectancy extension structure of high-temperature piping

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;
• and
• lowering 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, and
• the 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.