Analysis and Study on Residual Elastic Recovery of Spiral Welded Pipe（Part Ⅱ）

The relationship between the elastic recovery characteristics of the spiral welded pipe and the forming/sizing process thereof is discussed,resulting in identification of the problems relating to form-adjusting process by means of the outer formation device for making welded pipes with negative circumferential elastic come-back characteristics,and proposal of relevant countermeasures. Based on the results of systematic analysis and studies concerning the issue of residual elastic recovery of the spiral welded pipe,two math formulas for calculating the interior bending moment of residual elastic recovery are derived. Meanwhile,a brand-new mathematic control model for finished pipe blank is set up, showing the relationship between the interior residual stress σ^r and the three elements,i.e.,seam slot opening ΔL,radial displacement Δr and axial displacement ΔS, and thus being worth using for guiding in a certain extent the forming process design and manufacture equipment adjustment for spiral welded pipe production. Also analyzed and discussed is the specification for control of the welded pipe residual stress as specified under the supplementary technical terms for ordering of spiral welded pipes. Accordingly,some effective suggestions are proposed.