Why does the Stainless Steel Welded Pipe Have Wall Thickness Eccentricity?
Date:2022-03-08View:512Tags:Stainless Steel Welded Pipe,Wall Thickness Eccentricity
The most common defect of stainless steel welded pipe is the uneven wall thickness of the pipe. The relationship between the minimum deviation of the average wall thickness and the pipe making process is as follows: The pipe making equipment consists of a piercing machine, a pipe rolling machine, and a tension reducer. Take the stainless steel pipe blank as an example: The wall thickness deviation of the capillary from the piercer is at least 7.5%, reduced to 4.5% after extension rolling, increased to 7% after expansion, and reduced to 4.5% after tension reduction.
The eccentricity of the wall thickness of the stainless steel welded pipe will bring a series of adverse effects on the strength of the steel pipe and further cold working, thus affecting the economic benefits. When rolling large-diameter thick-walled stainless steel pipes, the local reduction increases, causing cracks and mechanical failure of the rolling mill.
Causes and influencing factors of eccentricity of wall thickness of stainless steel welded pipe
Cross-rolled piercing
In the process of skew rolling and piercing, the tube blank moves forward as it rotates. The spiral wall thickness eccentricity is generated in the perforated capillary, and the perforated capillary wall thickness distribution has multiple fluctuations with different amplitudes and different periods, showing a complex wall thickness deviation curve. The following Fourier analysis is performed on the wall thickness distribution, and the factors that cause the eccentricity of the stainless steel welded pipe wall thickness are deduced.
According to the respective period analysis, the eccentricity of stainless steel welded pipe wall thickness is mainly caused by the following factors:
1) The temperature of the blank section
2) Vibration of the plug (the center of the plug is inconsistent with the center of the mandrel)
Eccentricity of stainless steel welded pipe wall thickness caused by temperature difference of billet section
When the temperature of the blank section is uneven, the deformation resistance difference will be generated in the circumferential direction, and the pressure on the left and right sides will be out of balance; temperature difference.
Head accuracy and eccentricity caused by head vibration
The capillary threading test of the tube blank of small batch stainless steel welded pipe shows that if the center of the plug is misaligned or not round, when threading a capillary tube with a size of 136 x 8mm, using a plug with a maximum eccentricity of 1.5mm to thread a capillary tube is compared with a non-eccentric plug. It can be concluded that the wall thickness eccentricity caused by the precision of the plug will reach 0.3-0.8mm, indicating that the precision of the plug has a great influence on the eccentricity of the wall thickness of the stainless steel welded pipe; the vibration of the plug causes the force in the cross-rolling area to be insufficient during the process of cross-rolling and piercing. uniform, resulting in poor deformation resistance, resulting in uneven surrounding wall thickness.
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