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Why must be centered when hot-rolled thick-walled seamless steel pipes?

To know why the tube blank must be centered when hot-rolling thick-walled seamless steel pipes, we must first know what is the centering of the tube blank?

In order to align the nose of the hot-rolled seamless steel pipe with the front end of the tube blank during piercing, a shallow circular hole is processed at the front end of the tube blank before the tube blank is pierced. This process is called centering.

So why must the billet be centered when hot-rolling thick-walled seamless steel pipes? The purpose of centering the tube blank is to help the nose of the tip align with the axis of the tube blank during piercing, to prevent deviation during piercing, to reduce the uneven wall thickness of the front end of the capillary, and to improve the secondary bite conditions of oblique piercing and make the piercing process smooth get on.

The centering of the front end of the tube blank increases the depression of the front end after deformation, which is beneficial to align the nose of the plug and can reduce the uneven thickness of the front carbonyl wall. Especially when the thick-walled tube is worn, centering is more important. Because the compression of the thick-walled capillary tube is small, the depression after deformation of the front end is also small, and the diameter of the tip is much smaller than that of the tube blank (compared with the thin-walled tube) ), all of these increase the chance of misalignment when the head and nose of the abutment meets the front end of the tube blank. Therefore, in order to reduce uneven wall thickness and metal consumption, centering is important when rolling thick-walled tubes.

Centering can also improve the secondary bite conditions because of the increased compression in front of the head.
When some alloy steels are perforated, a smaller amount of compression is often used in order to achieve normal secondary biting and prevent uneven front-end wall thickness. At this time, centering is particularly important. If it is not centered, the tube blank and the nose The distance between the two parts is small, that is, the contact area is small. When the friction force of the roller dragging into the tube is less than the head resistance, the secondary bite cannot be achieved. That is to say, the contact area can be increased by centering, thereby increasing The large drag-in friction is conducive to the realization of the second bite. However, centering is not required under any circumstances. For example, when rolling small-diameter thin-walled tubes, whether or not centering has little effect on the uneven wall thickness of the front end, the tube blank can be pierced directly without centering. 

Tips: In case ASTM A53 Grade B in ERW (electric resistance welded) pipe, the weld seam shall be done the heat treatment with a minimum 1000°F [540°C]. In this way the no untempered martensite remains.
In case ASTM A53 B pipe in cold expanded, then expansion should not exceed 1.5% of the required OD.
 

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