Double-walled pipe construction

A length of double-walled pipe for a reverse-circulation drill string including:

• an outer pipe having a thickened box end at one end thereof and a thickened pin end at the other end;
• an inner pipe concentrically mounted in said outer pipe to provide a flow passage of annular cross-section between said pipes, the ends of said inner pipe being spaced axially inwardly of said box end and said pin end respectively;
• and means for mounting said inner pipe within said outer pipe, said means comprising, for each end of said inner pipe:
• a bushing slidably received on said inner pipe and spaced axially inwardly of the end thereof;
• at least three circumferentially spaced locating straps positioned between and welded to said bushing and the inner wall of said outer pipe;
• and a pair of annular locating sleeves slidably received on said inner pipe, one of said sleeves being positioned adjacent one end of said bushing and being welded to said inner pipe, the other of said sleeves being positioned adjacent the other end of said bushing and being welded to said inner pipe;
• whereby said inner pipe is concentrically mounted in said outer pipe while being free to rotate in said bushing and being restrained from axial movement relative to said outer pipe by interaction between said sleeves and the associated bushing.