Study on manufacture of large size pipe elbows by hydro‐bulging tubular single‐curvature polyhedron

This paper presents a method to manufacture pipe elbows by hydro‐bulging a tubular single‐curvature polyhedron. The basic idea is: first to build an enclosed tubular single‐curvature polyhedron using sector single‐curvature shell plates; then hydro‐bulge the polyhedron to make the tubular single‐curvature polyhedron deform plastically into a smooth double‐curvature tubular polyhedron; finally to cut the polyhedron into pipe elbows. Main technology steps are: first, to cut steel sheet plates into sheet blanks; second, to form the sheet blanks into single‐curvature cylindrical shells; third, to assemble and weld the single‐curvature cylindrical shells into an enclosed tubular single‐curvature polyhedron; fourth, to hydro‐bulge the polyhedron; fifth, to cut the polyhedron hydro‐bulged to get pipe elbows. This paper also describes a tubular single‐curvature polyhedron hydro‐bulging experiment. The results show that the single‐curvature polyhedron hydro‐bulging technology can be used to manufacture pipe elbows of a large size.