Patent ID: 6186182
Filing Date: 2001-02-13
Classification: F02M,F16L

Abstract:
A double-walled spiral pipe comprising:an outer wall 10 having a cylindrical shape, said outer wall 10 being prepared by winding spirally a coated steel plate 11 having corrugations 12; and an inner wall 20 having a cylindrical shape, said inner wall 20 being contacted with the wave bottom of the corrugations of said outer wall 10, and comprising semi-circular portions 22a or small corrugations 22c in order to cover the wave bottom of the corrugations of the outer wall such that a plane surface or half small corrugation is formed between said semi-circular portions 22a or other half small corrugations 22c whereby said inner wall 20 can be contracted or elongated depending upon a change of the pitch of the corrugations of said outer wall 10.