PRINCIPLE OF TRANSVERSAL FORMATION OF STRAIGHT-SEAM WELDED PIPE AND THE APPLICATION （Ⅰ）

With mathematical deduction, four transversal formation processes are systematically established, i.e. rim-bending formation, center-bending formation, circumference-bending formation and comprehensive bending formation, which provides aneasy computing method and theoretical basis for type-selection and pass design of welded pipe plant and reference for modification of the pass system of welded pipe mill as well.