Pipe Blank Research Articles

Numerical Analysis of Temperature Fields and Thermal Stress Fields in Heating Process of Large-Diameter Seamless Steel Pipe Blanks

Abstract In the piercing process of large-diameter seamless steel pipe blanks after heating, severe lateral cracks easily occur on the surface of pierced pipe blanks owing to the effects of the large temperature difference and thermal stress during the heating phase, influencing the finished product ratio and the safety and stability of use. Therefore, obtaining pipe blanks with uniform temperature distributions and low thermal stress peaks is the basis for the quality assurance of seamless pipes. In this paper, a study was conducted with large-diameter TP321 seamless pipe blanks with an example. The heating process of the pipe blank was investigated from two perspectives, temperature fields and thermal stress fields. Moreover, the effects of heating rate, initial furnace temperature, and hot-charging temperature were quantitatively analyzed. It was found that the peaks of the temperature difference and thermal stress both occurred at the early stage of heating. The temperature field and thermal stress distribution of the pipe blank gradually changed during heating. At the initial stage of heating, the temperature at the outer diameter edge was the highest, and the maximum thermal stress zones were concentrated on the inner hole edge and external surface. At the late stage of heating, the highest temperature zone and the maximum thermal stress zone were both focused on the inner hole surface. Lower initial furnace temperature and higher hot-charging temperature were more conducive to decreasing the maximum temperature difference and peak thermal stress, while the changes in heating rate had insignificant effects.

Simulation of vibration piercing of pipe blank at press

In some cases, the processes of piercing or expanding pipe blanks involve the use of high-frequency active vibrations. However, due to insufficient knowledge, these processes are not widely used in the practice of seamless pipes production. In particular, the problems of increasing the efficiency of the processes of piercing or expanding a pipe blank at a piercing press using high-frequency vibrations are being solved without proper research and, as a rule, by experiments. The elaboration of modern technological processes for the production of seamless pipes using high-frequency vibrations is directly related to the choice of rational modes of metal deformation and the prediction resistance indicators of technological tools and the reliability of equipment operation. The creation of a mathematical model of the process of vibrating piercing (expansion) of an axisymmetric pipe blank at a piercing press of a pipe press facility is an actual task. A calculation scheme for the process of piercing a pipe plank has been elaborated. A dependence was obtained characterizing the speed of front of plastic deformation propagation on the speed of penetration of a vibrated axisymmetric mandrel into the pipe workpiece being pierced. The dynamic characteristics of the occurrence of wave phenomena in the metal being pierced under the influence of a vibrated tool have been determined, which significantly complements the previously known ideas about the stress-strain state of the metal in the deformation zone. The deformation fields in the zones of the disturbed region of the deformation zone were established, taking into account the high-frequency vibrations of the technological tool. It has been established that the choice of rational parameters (amplitude-frequency characteristics) of the vibration piercing process of a pipe blank results in significant increase in the efficiency of the process, the durability of the technological tool and the quality of the pierced blanks.

Continuous Shaping of Welded Straight-Seam Pipe in the Open Stands of a Pipe-Welding System

Physical and computer modeling of continuous shaping is described. In the experiments, strip workpieces undergo continuous shaping on a TESA 10-50 pipe-electrowelding system for pipe of diameter 50 mm with wall thickness 1 mm. The pipe blanks are shaped in horizontal and vertical shaping stands, with estimation of the geometric parameters. Single-radius grooves are used on the rollers. The forces affecting the geometry of the pipe blank are determined. Analysis of the workpiece geometry reveals defects of corrugation type on its right edge between the second edging stand and the third shaping stand. A similar defect appears on the left edge in the section between the third shaping stand and third edging stand. To eliminate defects in the shaping section, the horizontal stands are adjusted so that the forces at the drives are the same. Then the relevant forces are again determined: the tractional forces of the drives; the resistance to strip motion in the stands; and the vertical shaping forces. In calculating the forces, the basic parameters are determined by two methods. In the first, the geometric parameters of the pipe blank and the parameters in the bending section are taken into account, with allowance for deformation outside of the contact zone. In the second, the contact interaction of the pipe blank and the shaping tool over the deformation cross section is taken into account. The discrepancy between the calculation results and the experimental data is 8–12%. After correcting the shaping parameters and adjusting the roller grooving, defect-free pipe blanks are shaped. According to comparison of the calculated and experimental trajectories of the edges of the workpiece over the height and width in the stands, the discrepancy is 6–9%. In investigating the geometric parameters of the deformation region, the bending zones with and without contact are taken into account, as well as the springback section. The shaping parameters of the pipe blank are calculated in uniform and roller shaping zones. Analysis of the results shows that shaping of the workpiece corresponds to the assumptions regarding the change in its geometry in roller grooves.

Numerical Analysis of Flow Fields and Temperature Fields in a Regenerative Heating Furnace for Steel Pipes

In the production process of large-diameter seamless steel pipes, the blank heating quality before roll piercing has an important effect on whether subsequently conforming piping is produced. Obtaining accurate pipe blank heating temperature fields is the basis for establishing and optimizing a seamless pipe heating schedule. In this paper, the thermal process in a regenerative heating furnace was studied using fluent software, and the distribution laws of the flow field in the furnace and of the temperature field around the pipe blanks were obtained and verified experimentally. The heating furnace for pipe blanks was analyzed from multiple perspectives, including overall flow field, flow fields at different cross sections, and overall temperature field. It was found that the changeover process of the regenerative heating furnace caused the temperature in the upper part of the furnace to fluctuate. Under the pipe blanks, the gas flow was relatively thin, and the flow velocity was relatively low, facilitating the formation of a viscous turbulent layer and thereby inhibiting heat exchange around the pipe blanks. The mutual interference between the gas flow from burners and the return gas from the furnace tail flue led to different flow velocity directions at different positions, and such interference was relatively evident in the middle part of the furnace. A temperature “layering” phenomenon occurred between the upper and lower parts of the pipe blanks. The study in this paper has some significant usefulness for in-depth exploration of the characteristics of regenerative heating furnaces for steel pipes.

Edge geometry of pipe blanks produced by JCOE flexure

For the shaping of welded straight-seam large-diameter pipe in the TESA 1420 production line, methods are proposed for calculating the geometric parameters of the edge of the blank and the profile of the deforming tool. The edge geometry obtained on an edge-bending press is compared when using surface tools of involute and single-radius type. For tools of single-radius type, edge geometry consistent with the required shaping quality may be produced. For the edge-bending presses, a method of calculating the edge geometry in loading and unloading is outlined. The height of the bent edge, the residual radii of curvature, and the coordinates of the loading and unloading points at the external and internal edge contour of the pipe blank are determined. The coordinates of the edge formed by a tool with an involute profile are also calculated. The involute tool profile is universal on passing from one type of tool to another within a standardized group. The calculation permit conversion from an involute edge profile to a multiradial profile, followed by determination of the fixed coordinates of the points of the blank after springback. On the basis of those coordinates, the output edge geometry is estimated. Within the 1220–1420 mm standardized group, the longitudinal edge deformation for the 1220 × 10 mm type is calculated. Standardization is found to be much simpler with a single- radius tool profile. For edge-bending presses, a method of calculating the edge parameters of the pipe blank when using a tool with an involute contact profile is developed and tested in industrial conditions. Single- radius calibration of the profile of the edge-bending tool is proposed, such that fixed time coordinates are ensured. These are analogous to the coordinates with an involute punch profile. The blank’s weighted mean radius of curvature maximizes the agreement of the coordinates of the blank profile at fixed points in both approaches. (The maximum discrepancy is no more than 6–7%.)

Shaping of sheet to produce large-diameter welded pipe

The quality of welded pipe (diameter 508–1420 mm; wall thickness 8–48 mm) of strength class up to K80 (X100) is investigated. Plastic shaping is simulated, with quantitative estimation of the stress–strain state of thick-walled pipe blanks in TESA 1420 presses during edge bending and stepwise shaping. The corresponding computer program permits calculation of the setup of the equipment and determination of the geometric parameters of the pipe blank specified in the standards. Theoretical results are presented for a range of large-diameter pipe produced on the TESA 1420 system.

Production of continuous-cast pipe blank without large nonmetallic inclusions

The quality of metal in continuous-cast pipe blanks is investigated, for different steel-production technologies. The presence of large nonmetallic inclusions is largely due to disruptions in the continuouscasting technology. Other significant factors are nonoptimal modification of the nonmetallic inclusions and problems in ladle treatment. Measures ensuring acceptable content of nonmetallic inclusions are developed and tested.

Expansion of pipe blanks

The development of new shaping technologies for pipe blanks requires simulation of the stress and strain fields, which permits assessment of the limiting stress and strain values. The stress–strain state of a pipe blank in expansion (including nonuniform expansion) is analyzed in the present work. Joint solution of the equilibrium equations and plasticity condition is employed here; that is the traditional approach. Analytical dependences of the stress in the wall of the pipe blank on the technological parameters are obtained; the basic formulas for estimating the strain are also presented. Experiments confirm the results.

Shaping of pipe blanks on specialized bending equipment

A method is proposed for measuring the profile of the pipe blank in shaping. In the production of welded large-diameter straight-seam pipe, the blank breaks away from the bending roller in the deforming region. Such breakaway is investigated in a bending system. Experiments show that, in the breakaway zone, the blank has complex curvature. Software is developed for calculating the coordinates and radii of curvature of the blank surface from photographs of the deformation region. The profile of the pipe blank is plotted with allowance for the change in curvature at breakaway from the bending roller. Breakaway is taken into account in calculating the radius of curvature after unloading.

Shaping of pipe blanks in the edge-bending press of the TESA 1420 pipe-electrowelding line

Contact geometric measurements of pipe blanks in the edge-bending section of the TESA 1420 pipe-electrowelding line are made by a new method. The influence of the pipe blank’s edge geometry on the shape of the edge zone after the subsequent processes is assessed. The stages of the experiment are outlined. The experimental data are obtained in the form of the coordinates of points on the edge. Measurements of the edge geometry by different methods are compared. The use of photographic-survey measurements is promising for use in the production of large-diameter pipe.

Production of pipe blanks from corrosion-resistant duplex steel

The introduction of pipe-blank production (blank diameter 180 mm) from corrosion-resistant duplex steel (UNS S 31803, UNS S 32205, DIN 1.4462, and 03X22H5AM3) at PAO Dneprospetsstal’ plant is considered. The chemical composition of the melts at PAO Dneprospetsstal’ and pipe blank produced from duplex at traditional foreign suppliers is compared. The content of nonmetallic inclusions is studied, as well as the distribution and content of ferrite-austenite phases, the impact strength, the resistance to pitting corrosion, and the high-temperature deformability.

Thick-walled centrifugally cast 08X18H10T steel blank for seamless-pipe production

Thick-walled pipe blanks made by centrifugal casting of corrosion-resistant 08X18H10T steel are investigated. These blanks are intended for subsequent hot pressing of pipe (diameter 89 mm, wall thickness 12 mm). The macrostructure of the castings is studied, as well as the mechanical properties of cast and heat-treated tangential, transverse, and longitudinal samples. The defects observed in the centrifugally cast pipe are analyzed. The resistance of the cast metal to deformation is assessed, as well as the technological plasticity of the cast pipe blank.