Investigation of the method of the accuracy increase of hot-rolled pipes under expansion

At present, the main characteristics of steel pipes are their mechanical properties, surface finish and dimensional accuracy. Accuracy is one of characteristics that defines the service life in such industries as machine building, oil and petrochemical industry, nuclear power engineering, etc. In domestic and foreign standards for hot-rolled pipes there are no dimensionless accuracy factors taking into account the statistical distribution of sizes. This aspect complicates the analysis of dimensional accuracy of products, as well as the assessment of its increase feasibility. For this reason, the accuracy factor that takes into account the statistical distribution of pipe sizes before and after deformation is offered by authors. Thus, the influence of different technological factors may be assessed and calculation of the accuracy factor for pump and compression pipes can be carried out. The effective way to increase the accuracy of the internal diameter and surface finish of hot-rolled pipes is the calibration operation by means of pipe expansion on the mandrel. With the aim to assess calibration efficiency, computer simulation in the finite element modelling package Deform-3D was carried out. Pump and compressor pipes with different internal channel diameters within the state GOST standard were chosen as a simulation object. Computer simulation showed features of forming pipes under expansion on the mandrel. As a result of the experiment the graph of accuracy changes before and after expansion was obtained and recom¬mendations were formulated on their basis. Finite element simulation showed that under optimum conditions of the accuracy of the pipe internal channel can be increased more than three times.