Patent ID: 7866378
Filing Date: 2011-01-11
Classification: B23P,F16L,F25B,F28D,F28F,Y10T

Abstract:
1. A double-wall pipe comprising: an outer pipe; and an inner pipe disposed inside the outer pipe, the inner pipe having thereon three or more separate ridge portions defining an outer portion of an outer surface of the inner pipe, the ridge portions defining a groove portion extending in a longitudinal direction of the inner pipe, the groove portion defining an inner portion of the outer surface of the inner pipe; wherein: the three or more separate groove portions are three or more separate helical grooves winding around the inner pipe and extending the longitudinal direction; each of the helical grooves have a groove depth that is in a range of 5% to 15% of an outside diameter of the inner pipe; the outer pipe and the inner pipe are bent to have a straight portion extending straightly, and a bend portion bent from the straight portion; the outer pipe has an inside diameter that is larger than an outside diameter of an imaginary cylinder defined by an outer surface of the ridge portions of the inner pipe, in the straight portion; the outside diameter of the imaginary cylinder defined by the outer surface of the ridge portions of the inner pipe in the straight portion is in a range of 0.7 to 0.95 of the inside diameter of the outer pipe in the straight portion; and the outer pipe is deformed in a radial direction in the bend portion to radially squeeze the inner pipe such that the three or more separate ridge portions of the inner pipe are all in direct contact with an inside surface of the outer pipe.