South Ural State University, Chelyabinsk, Russia¹ ; Russian Research Institute of the Tube and Pipe Industry (RusNITI), Chelyabinsk, Russia²:

A. V. Vydrin, Dr. Eng., Prof., Dept. of Machinery and Technologies for Materials Forming¹, Chief Researcher²

Russian Research Institute of the Tube and Pipe Industry (RusNITI), Chelyabinsk, Russia:

D. Yu. Zvonarev, Cand. Eng., Head of the Laboratory for Modeling Technological Processes
M. A. Pavlova, Senior Engineer, Laboratory for Modeling Technological Processes, e-mail: pavlova@rosniti.ru

Volzhsky Pipe Plant, Volzhsky, Russia:

A. S. Zhukov, Quality Director

The main factor determining the possible appearance of continuity defects in hotpressed pipes is the physical nature of the material subjected to deformation, namely, its plasticity. Alloying of a metal contributes to a decrease in its plasticity and an increase in the resistance to plastic deformation, which, on the one hand, increases the stress level during hot deformation, and, on the other hand, reduces the threshold stress value corresponding to the onset of metal fracture. The introduction of computer simulation tools, in particular software products based on the finite element method, made it possible to perform an analytical study of the features of the stress-strain state of the metal during hot pressing of steel pipes. Particular attention in the modeling is paid to the deformation conditions of the surface layers of the metal, since one of the characteristic surface defects of hot-pressed pipes is cracks and ruptures. The dependences of the stress-strain state on the technological parameters of the pressing process are revealed, namely, the nature of the change in the stress-strain state of the surface layers of the pressed shell along the deformation zone length, the effect of temperature, elongation coefficient and friction coefficient on the change in the stress-strain state are determined, the degree of the plasticity resource use by the Kolmogorov failure criterion is assessed. On the basis of the results obtained, a set of theoretical and experimental studies was carried out to investigate the mechanisms of the formation of surface defects in hot-pressed pipes, technological parameters and technological tool parameters that contribute to the elimination of surface defects were determined.

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