METHOD FOR WELDING ENAMELED TUBES Russian patent published in 2003 - IPC

FIELD: welding, namely processes for welding tubes, for example enameled tubes, possibly at making, restoring gas- and oil mains pipelines, at transporting fluids containing oxygen, carbon dioxide or hydrogen sulfide, mineral salts at wide range of temperature and pressure values. SUBSTANCE: method comprises steps of using steel sleeves with inner corrosion resistant coating and with thickness of walls exceeding no more than by 1.3 times thickness of tube walls; welding sleeves to outer surface of steel tubes by angular seam at side of sleeve end opposite relative to end of tube butt and at shifting other end of sleeves relative to end of butt; applying enamel layer onto surfaces of openings of steel tubes; then dressing edges of tubes for welding in such a way that dressed edges are spaced from sleeves by distance equal to 0.5 - 1.0 of thickness value of tube wall at opening angle 25 - 40 degrees relative to vertical axis and with blunting corresponding to 0.5 -0.7 of thickness value of tube wall. Then cleaning is performed for further applying of additional enamel layer onto blunting surface and onto tube opening surfaces adjoining to butt. Assembling is realized without in butt gap. Welding for joining tubes is performed by two welded seams. First seam is made along thickness equal to summed thickness value of tube and sleeve. Further seams are made at cooling root seam until temperature at least twice less than enamel melting temperature. It provides simplification of method and its cost lowered at least by 5 times. EFFECT: enhanced quality of welded thin-wall tubes, integrity of enamel coating onto inner surface of thin-wall tubes, corrosion protection of root seams. 5 dwg, 1 ex