Pipe usually has thicker walls and may be threaded or welded , where tubes have thinner walls , and needsspecial joining techniques such as ` brazing ' , ` compression fitting ' , ` crimping ' , or for plastics , ` solvent welding ' . Pipe normally has thicker walls and may be threaded or welded , where tubing is thinner-walled and requires special joining techniques such as `` brazing '' , `` compression fitting '' , `` crimping '' , or for plastics , `` solvent welding '' .