JPS57156844A - Manufacture of double pipe - Google Patents

Abstract

PURPOSE:To obtain an auto-frettage double pipe forming a high degree of fitting at a working temperature, by oppositely superposing in layers an outside pipe whose coefficient of linear expansion is larger than that of the inside pipe, on the inside pipe, expanding the inside pipe at a higher temperature than an actual working temperature, bringing both the pipes to yield plastic deformation, and after that, contracting the pipes. CONSTITUTION:For instance, in order to manufacture a pipe laid in a refrigerated warehouse, in a factory whose average temperature through a year is TH, an outside pipe having the inside diameter DOTH and an inside pipe having the outside diameter DiTH(DOTH>DiTH) made of carbon steel whose coefficient of expansion is alpha0, alphai, respectively (alpha0>alphai) and invar are manufactured. Subsequently, the inside pipe is superposed oppositely in layers in the outside pipe, the inside pipe is expanded by hydraulic pressure by use of water whose temperature is TH, is brought into press-contact with the outside pipe, both the pipes are brought to yield plastic deformation, and the diameter of both the pipes is contracted by releasing the hydraulic pressure by a designed diameter epsilon0. The outside and inside pipes become D'OTH, D'iTH, respectively, and a temporary double pipe having a degree of fitting of a difference DELTAD between both the pipes is obtained. When they are laid at a working temperature of a low temperature in the refrigerated warehouse, D'iTH and D'CTH are contracted to DiTL and DOTL, respectively, a degree of fitting DELTAD' of DiTL-DOTL is formed automatically, and the inside and outside pipes are coupled and clamped tightly.