Causes of uneven wall thickness of large diameter seamless pipe

Large-diameter seamless steel pipe, as the name suggests, is a seamless steel pipe with a relatively large diameter. The main production processes are hot-rolled large-diameter seamless steel pipes(hot-rolled seamless pipe)  and heat-enlarged diameter seamless steel pipes.

The problem of uneven wall thickness of large-diameter seamless steel pipes is relatively common in the production of seamless steel pipes, and it is also a headache for customers. The unevenness of thick-walled seamless steel pipes is mainly reflected in uneven spiral walls, uneven linear wall thickness, and slightly thicker and thinner ends at the head and tail.

The inducing factors for the unevenness of large-diameter seamless steel pipes are uneven wall thickness caused by adjustment reasons such as the inclination of the cold-rolling center line of the cutting machine, the different inclination angles of the two hot-rolled strips, or the insufficient front reduction of the top. The entire length of the tube extends in a spiral shape. The important preventive measure is to adjust the cold rolling center line of the cutting machine so that the inclination angles of the two hot-rolled strips are the same, and adjust the cold drawing machine according to the basic parameters obtained from the cold rolling table.

The reason for the uneven linear wall thickness is that the height of the pre-threading saddle of the mandrel is not adjusted properly. The mandrel contacts the capillary tube on a certain side during pre-threading, causing the surface temperature of the capillary tube to drop too quickly, resulting in uneven wall thickness and even dent defects. . The gap between the hot rolled strips in the rolling mill is too small or too large. Deviation of the centerline of the cold drawing machine. The uneven reduction amount of single and double frames will cause the seamless pipe to be ultra-thin (ultra-thick) in the single-frame direction and ultra-thick (ultra-thin) in the double-frame direction. The important preventive measure is to control the height of the pre-piercing saddle of the mandrel to ensure the centering of the mandrel and the capillary tube. When replacing plate holes and cold-rolled model specifications, it is necessary to accurately measure the hot-rolled strip gap to ensure that the actual hot-rolled strip gap is consistent with the cold-rolled table.

The reason for the uneven wall thickness at the head and tail is that the front end of the large-diameter seamless steel pipe is sloped, and the bend is too large. The tilt of the relief hole of the large-diameter seamless steel pipe can easily cause uneven wall thickness at the head of the seamless pipe. When holes are broken, the widening index value is very large, the transmission ratio of hot-rolled strip steel is too high, and cold rolling is unstable. Unstable steel thrown by the cutting machine can easily cause uneven wall thickness at the end of the capillary tube. The preventive measures are to check the quality of large-diameter seamless steel pipes, prevent the front-end engineers of large-diameter seamless steel pipes from cutting slopes, and reduce the amount of pressure. The replacement of plate holes or maintenance should be done with the correct holes. A lower hole breaking speed is used to ensure the stability of cold rolling and the accuracy of thick rough walls. When the hot-rolled strip transmission ratio is adjusted, the matching guide plate is also adjusted accordingly.

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