METHOD FOR JOINING TUBES HAVING INNER CEMENT-SAND COATING Russian patent published in 2003 - IPC

FIELD: machine engineering, namely non-detachable joints, possibly used in pipelines for housing and also in oil production industry branch. SUBSTANCE: method comprises steps of placing thin-wall sleeves of corrosion resistant metal inside end portions of tubes along distance subjected to thermic influence at welding process and joining prepared end portions of tubes by welding; placing said sleeves before applying cement-sand coating; at applying cement-sand coating placing sleeve ends at side of tube ends in such a way that they protrude outside tube ends by value equal to thickness of cement-sand coating; after cement setting rolling-in said ends or using sleeves with inner surface in the form of truncated cone whose small base is turned to welded ends of tubes; after welding sealing annular recess formed between ends of sleeves and coating, for example by pumping cement "milk" or by applying cement-sand coating. Method provides protection of coating material against destructive action of welding heat. EFFECT: increased useful life period of joint, less labor and material consumption, simplified joining process. 3 cl, 5 dwg