PURPOSE: To improve heat transfer performance by a method wherein a ceramic coating layer, having a plurality of detecting flow passages of cracked condition, is provided integrally between an outer tube and an inner tube, in a heat transfer tube consisting of the outer tube and the inner tube combined concentrically in double layers under the condition of contacting closely.
CONSTITUTION: A ceramics coating layer 3, having a plurality of detecting flow passages of the condition of axial cracks, is provided integrally between an outer tube 1 and an inner tube 2, in a heat transfer tube, provided with the inner tube 2 and outer tube 1 concentrically and provided with an annular gap for detecting leakage between both tubes 2, 1 while being used for a large- size steam generator, heat exchanger and the like. The cracks provided on the ceramics coating layer 3 are formed by a method wherein pressure fluid is forced into the inner tube 2 to expand the inner tube 2 together with the outer tube 1 and the ceramics coating layer 3 outwardly whereby the cracks, divided circumferentially and generated in a direction along the axis of the tube, are formed. According to this method, effective leakage detecting flow passages can be obtained while securing prominent heat transfer performance.
KOMATA IPPEI
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