Concentric, insulated tubular conduits and method for assembly

Abstract

Concentric, tubular sections are assembled by first securing annular centralizers and insulation about the external surface of the smaller diameter tube while the tube is horizontally disposed. The larger tube is then vertically aligned and lowered into a recessed area formed below the assembly area work level. A lifting cable, secured at one end to a lifting device, is extended through the smaller diameter tube and attached to a hoisting arrangement that vertically orients the tube concentrically over the larger diameter tube. Spring-loaded legs on the lifting device are manually retracted radially to permit the smaller tube to be lowered concentrically through the larger tube. The inner tube is lowered until the legs spring radially outwardly to engage the base of the larger tube. The entire assembly may then be lifted as a unit by the hoist with the lifting device, establishing the axial positions of the two tubes relative to each other. The centralizers closely engage the internal surface of the larger tube to centralize the inner tube and to prevent relative radial movement between the tubes. The external surface of the centralizers is specially configured to provide an interrupted line contact with the external tube, and the centralizers are rotated relative to each other to circumferentially displace points of contact with the external tube to minimize heat transfer.

What is claimed:  
     
         1 . A centralizing ring for spacing an inner tube annularly from a surrounding outer tube comprising: 
 a curving external surface contour on said ring for forming a line contact with a cylindrical surface in said inner or outer tube; and    radially recessed areas in said external surface contour circumferentially spaced about said ring for circumferentially disrupting said line contact whereby heat transfer between said inner and outer tube is reduced.    
     
     
         2 . A centralizing ring as defined in  claim 1  wherein said external surface contour is carried on the radially outer surface of said ring.  
     
     
         3 . A centralizing ring as defined in  claim 2  wherein said ring includes a circumferential gap whereby said ring can be diametrically expanded for assembly onto an inner tube.