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

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.

CALCULATION OF PARAMETERS OF CHANNEL THROTTLING OF EXPENSIVE ELEMENTS OF FIRMWARE

The article considers possible options for supplying coolant to the cutting and deforming teeth of multi-pronged firmware for processing deep holes. The advantages and disadvantages of each scheme are indicated. It is noted that when the lubricant-cooling liquid (coolant) is pushed through straight or screw slotted grooves made on the outer surface of the mandrel teeth, "damping pads" are created on the surface to be processed, which improve the mandrel process and reduce wear of the stitches for processing deep holes. For each of the schemes, a method for calculating the coolant flow rate is described, depending on the parameters of the slotted grooves for the coolant flow and the pressure of its supply. The ability to calculate the consumption of coolant through the cutting and deforming teeth of multi-toothed stitches allows you to correctly assign processing modes and, thereby, increase the technical and economic efficiency of mechanical processing of long pipe blanks.

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.