8 major defects of seamless steel pipe
Characteristics and causes of 8 major defects of seamless steel pipe
If there are some defects in seamless steel pipes, it will undoubtedly have a fatal impact on the quality of our products. So how to avoid these defects? Then we need to understand the causes of these defects. Let's introduce the specific causes of the eight defects of seamless steel pipe:
1. Seamless steel pipe folding
It is a kind of straight or spiral, continuous or discontinuous state existing on the outer or inner surface of seamless steel pipe. The main reason for the folding is that the quality of the tube is poor, there is folding itself, or there are inclusions, serious scratches and cracks on the surface, there are edges and corners at the grinding place, and the folding occurs after drawing and extending. In order to avoid folding, we should improve the quality of pipe material and pay attention to inspection and grinding.
2. Seamless steel pipe crack
It refers to the small cracks on the inner and outer surfaces of seamless steel pipes, which are distributed in a straight line or a spiral line, with a depth of 1mm or more, continuous and discontinuous. According to the analysis of Shandong jute tube industry, the causes are: there are subcutaneous bubbles and inclusions in the hot rolled tube blank, there are cracks or deep pockmarks on the steel tube before drawing, and there are longitudinal scratches or scratches in the hot rolling or cold drawing processes. The prevention of crack formation also lies in improving the quality of tube blank and strengthening the inspection and grinding of tube material. At the same time, it is necessary to avoid pitting, scratch and scratch in the process of cold drawing.
3. Scratch of seamless steel pipe
The defect is characterized by long and short scratches with longitudinal straight lines on the inner and outer surfaces of seamless pipes, most of which are groove like, but may also be raised stripes. The main causes of scratch (scratch) are as follows: there is internal scratch on the pipe material, which can not be eliminated during drawing, there is oxide scale die stuck on the steel pipe, the strength and hardness of the die are not enough or uneven, the die is broken and worn, the hammer head is not good, and the sharp edges and corners of the transition part of the hammer head damage the die, etc. In order to prevent scratch and scratch, we should improve the quality of each preparation process before drawing, and use the mould with high strength, hardness and finish.
4. Pit of seamless steel pipe
This is one of the most common surface defects of seamless pipe. Some of them are periodic and some are irregular. The pit is caused by the oxide scale or other hard dirt pressed into the steel pipe surface during the drawing or straightening process, or by the warping and peeling of the original steel pipe surface. Shandong jute Pipe Co., Ltd. points out that the measures to prevent the pit are to carefully check the pipe material and remove the defects such as warped skin, keep the working site, tools and lubricants clean, and prevent the oxide skin and dirt from falling on the surface of the steel pipe.
When there are round or sharp spiral marks on the outer surface of seamless steel pipe, the straightener shall be checked. Due to the incorrect position and angle of the straightening roller, the steel pipe rubbed the shoulder at the edge of the straightening roller during straightening, and there were worn grooves on the straightening roller. If both ends of the steel pipe were bent too much, there might be pits on the outer surface of the steel pipe.
5. Pitted surface of seamless steel pipe
The utility model is characterized in that the surface of the steel pipe is provided with small pits in the form of flakes and dots. The main cause of pitting is pitting corrosion during acid pickling. After annealing, the iron oxide scale is too thick and straightened, and then pressed into the steel pipe surface to form pitting. The steel pipe is kept in a humid environment, and even pitting corrosion occurs after water inflow, and pitting is formed after rust removal.
6. Seamless steel pipe spot
As seamless steel pipes are not treated in time (such as drying) due to contact with water (or water vapor) in the process of processing or storage, traces left after water evaporation are called water spots, such as long contact time with water, or rust spots will be formed when there are corrosive substances in the water. Generally, there is no depth of water spots, and rust spots often corrode to the steel pipe surface, and there will still be pockmarks after removal.
7. Seamless steel pipe warping
It is characterized in that the inner and outer surfaces of seamless steel pipes have thin sections separated from the metal matrix, some of which are massive and discontinuous, rooting or not rooting on the pipe wall, but can not peel off naturally. The causes include poor steel quality, subcutaneous bubbles, which are exposed after cold drawing; the warped skin generated during hot rolling is not removed from the tube blank and brought to cold drawing; the original deep and angular transverse pits on the tube form warped skin after drawing.
8. Seamless steel pipe scarring
The inner and outer surfaces of steel pipes are not removed in time due to the defects such as folding and warping skin. In the subsequent processing, thin sheets that cannot be separated from the metal matrix are formed, some of which are lumpy and discontinuous. They take root or do not take root on the pipe wall, but cannot peel off naturally, which is called scabbing. The surface defects must be checked and removed in time to eliminate scabs.
If there are some defects in seamless steel pipes, it will undoubtedly have a fatal impact on the quality of our products. So how to avoid these defects? Then we need to understand the causes of these defects. Let's introduce the specific causes of the eight defects of seamless steel pipe:
1. Seamless steel pipe folding
It is a kind of straight or spiral, continuous or discontinuous state existing on the outer or inner surface of seamless steel pipe. The main reason for the folding is that the quality of the tube is poor, there is folding itself, or there are inclusions, serious scratches and cracks on the surface, there are edges and corners at the grinding place, and the folding occurs after drawing and extending. In order to avoid folding, we should improve the quality of pipe material and pay attention to inspection and grinding.
2. Seamless steel pipe crack
It refers to the small cracks on the inner and outer surfaces of seamless steel pipes, which are distributed in a straight line or a spiral line, with a depth of 1mm or more, continuous and discontinuous. According to the analysis of Shandong jute tube industry, the causes are: there are subcutaneous bubbles and inclusions in the hot rolled tube blank, there are cracks or deep pockmarks on the steel tube before drawing, and there are longitudinal scratches or scratches in the hot rolling or cold drawing processes. The prevention of crack formation also lies in improving the quality of tube blank and strengthening the inspection and grinding of tube material. At the same time, it is necessary to avoid pitting, scratch and scratch in the process of cold drawing.
3. Scratch of seamless steel pipe
The defect is characterized by long and short scratches with longitudinal straight lines on the inner and outer surfaces of seamless pipes, most of which are groove like, but may also be raised stripes. The main causes of scratch (scratch) are as follows: there is internal scratch on the pipe material, which can not be eliminated during drawing, there is oxide scale die stuck on the steel pipe, the strength and hardness of the die are not enough or uneven, the die is broken and worn, the hammer head is not good, and the sharp edges and corners of the transition part of the hammer head damage the die, etc. In order to prevent scratch and scratch, we should improve the quality of each preparation process before drawing, and use the mould with high strength, hardness and finish.
4. Pit of seamless steel pipe
This is one of the most common surface defects of seamless pipe. Some of them are periodic and some are irregular. The pit is caused by the oxide scale or other hard dirt pressed into the steel pipe surface during the drawing or straightening process, or by the warping and peeling of the original steel pipe surface. Shandong jute Pipe Co., Ltd. points out that the measures to prevent the pit are to carefully check the pipe material and remove the defects such as warped skin, keep the working site, tools and lubricants clean, and prevent the oxide skin and dirt from falling on the surface of the steel pipe.
When there are round or sharp spiral marks on the outer surface of seamless steel pipe, the straightener shall be checked. Due to the incorrect position and angle of the straightening roller, the steel pipe rubbed the shoulder at the edge of the straightening roller during straightening, and there were worn grooves on the straightening roller. If both ends of the steel pipe were bent too much, there might be pits on the outer surface of the steel pipe.
5. Pitted surface of seamless steel pipe
The utility model is characterized in that the surface of the steel pipe is provided with small pits in the form of flakes and dots. The main cause of pitting is pitting corrosion during acid pickling. After annealing, the iron oxide scale is too thick and straightened, and then pressed into the steel pipe surface to form pitting. The steel pipe is kept in a humid environment, and even pitting corrosion occurs after water inflow, and pitting is formed after rust removal.
6. Seamless steel pipe spot
As seamless steel pipes are not treated in time (such as drying) due to contact with water (or water vapor) in the process of processing or storage, traces left after water evaporation are called water spots, such as long contact time with water, or rust spots will be formed when there are corrosive substances in the water. Generally, there is no depth of water spots, and rust spots often corrode to the steel pipe surface, and there will still be pockmarks after removal.
7. Seamless steel pipe warping
It is characterized in that the inner and outer surfaces of seamless steel pipes have thin sections separated from the metal matrix, some of which are massive and discontinuous, rooting or not rooting on the pipe wall, but can not peel off naturally. The causes include poor steel quality, subcutaneous bubbles, which are exposed after cold drawing; the warped skin generated during hot rolling is not removed from the tube blank and brought to cold drawing; the original deep and angular transverse pits on the tube form warped skin after drawing.
8. Seamless steel pipe scarring
The inner and outer surfaces of steel pipes are not removed in time due to the defects such as folding and warping skin. In the subsequent processing, thin sheets that cannot be separated from the metal matrix are formed, some of which are lumpy and discontinuous. They take root or do not take root on the pipe wall, but cannot peel off naturally, which is called scabbing. The surface defects must be checked and removed in time to eliminate scabs.
