Method and equipment for manufacturing electric resistance welded steel pipe

A method of operating an electric resistance welded steel pipe manufacturing line comprising:

• (a) producing sample open, substantially tubular steel pipes from a steel strip as a testing sample by roll forming, said open, substantially tubular steel pipes each having an opening and two proximate, opposing edges adjacent to said opening, and having sample groove shapes having a sample groove height, said sample groove shapes being applied to each edge by tapering corner portions at inner and outer tubular surfaces of each one of said edges, and measuring said sample groove height;
• establishing through measurements obtained by variation of sample groove height an adjustment of a setting of a level of electric welding power to a value at which the seam Charpy test transition temperature is minimal as a function of said electric welding power, thereby establishing a relationship between groove height and welding electric power at which toughness of a weld is optimal;
• and
• (b) producing an electric resistance welded steel pipe as a product based upon said relationship according to the following steps:
• (i) forming an open, substantially tubular product pipe from a steel strip by roll forming as a product source, said open, substantially tubular steel pipe having an opening and two proximate, opposing edges adjacent to said opening, and having product groove shapes having a product groove height, said product groove shapes being applied to each edge by tapering corner portions at inner and outer tubular surfaces of each one of said edges;
• (ii) measuring said product groove height;
• (iii) obtaining a setting of a value of welding power at which toughness is optimal based on the measured product groove height and said relationship as obtained in step (a);
• (iv) welding both edges of the open, substantially tubular steel product pipe by electric resistance welding, wherein the welding power is set to said value at which toughness is optimal for the measured product groove height.