Written by Characteristics and causes of eight defects in seamless steel pipes
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 you need to understand the causes of these defects. The following Changzhou Precision Steel Pipe Blog will discuss with you the specific causes of the eight defects of seamless steel pipes:
1. Seamless steel pipe folding
It is a linear or spiral, continuous or discontinuous state existing on the outer or inner surface of seamless steel pipes. The main reason for folding is that the quality of the pipe material is poor, there are folds in itself, or there are inclusions, severe scratches and cracks on the surface, there are edges and corners at the grinding place, and folding occurs after drawing and extension. In order to avoid the occurrence of folding, the quality of the pipe material should be improved and attention should be paid to inspection and grinding.
2. Seamless steel pipe cracks
It refers to fine cracks distributed in straight lines or spiral lines on the inner and outer surfaces of seamless steel pipes, with a depth of 1 mm or more, and there are continuous and discontinuous ones. According to the analysis of Shandong Jute Pipe Industry, the reasons are: there are subcutaneous bubbles and subcutaneous inclusions in the hot-rolled tube billet, there are cracks or deep pits on the steel pipe before drawing, and longitudinal scratches or abrasions are generated during hot rolling or cold drawing. Preventing the formation of cracks also lies in improving the quality of the tube billet and strengthening the inspection and grinding of the tube material. At the same time, it is necessary to avoid pitting, scratches and abrasions on the tube during the cold drawing production process.
3. Scratches on seamless steel pipes
The defect is characterized by longitudinal straight-line scratches of varying lengths on the inner and outer surfaces of the seamless pipe, mostly in the shape of grooves, but may also be raised stripes. The main reasons for the scratches (scratches) are: there are internal scratches on the tube material, which are not eliminated during drawing, there is iron oxide remaining on the steel pipe, the mold sticks to the steel, the mold strength and hardness are insufficient or uneven, the mold is broken and worn, the hammer head is poor, and the sharp edges and corners of the transition part of the hammer head damage the mold, etc. In order to prevent scratches and abrasions, the quality of each preparatory process before drawing should be improved, and a mold with high strength, hardness and good finish should be used.
4. Seamless steel pipe pits
This is one of the most common surface defects of seamless pipes. Local depressions of varying areas are distributed on the surface of the steel pipe. Some are distributed periodically and some are irregular. The pits are caused by the iron oxide scale or other hard dirt being pressed into the surface of the steel pipe during the drawing or straightening process, or the peeling of the warping scale that originally existed on the surface of the steel pipe. Shandong Jute Pipe Industry pointed out that the measures to prevent pits are to carefully check the pipe material and remove defects such as warping scale, keep the workplace, tools and lubricants clean, and prevent iron oxide scale and dirt from falling on the surface of the steel pipe.
When there are smooth or sharp-edged spiral marks on the outer surface of the seamless steel pipe, the straightening machine should be checked. Due to the incorrect position and angle of the straightening roller, the steel pipe rubbed the convex shoulder of the straightening roller edge during straightening, the straightening roller had worn grooves, and the two ends of the steel pipe were bent too much, which may cause pits on the outer surface of the steel pipe.
5. Seamless steel pipe pitting
It is characterized by small pits in sheets and dots on the surface of the steel pipe. The main reason for the pitting is pitting during pickling, and the excessive thickness of the oxidized iron scale after annealing is pressed into the surface of the steel pipe after straightening to form pitting; the steel pipe is stored in a humid environment, and even pitting occurs after water enters, and pitting is formed after the rust is removed.
6. Seamless steel pipe spots
Since the seamless steel pipe is not treated in time (such as drying) when it comes into contact with water (or water vapor) during processing or storage, the traces left after the water evaporates are called water spots. Rust spots will be formed when it is in contact with water for a long time or when there are corrosive substances in the water. Water spots generally have no depth, while rust spots often corrode the surface of the steel pipe, and pitting will still exist after removal.
7. Seamless steel pipe warping
Its characteristic is that there are thin flakes on the inner and outer surfaces of seamless steel pipes that are partially separated from the metal matrix. Some of them are in blocks and discontinuous, rooted or not rooted on the tube wall, but cannot be peeled off naturally. The reasons for the occurrence are poor steel quality, subcutaneous bubbles, exposed after cold drawing; the warping produced during hot rolling is not removed from the tube blank until cold drawing; the original deep and angular transverse pits on the steel pipe form warping after drawing.
8. Seamless steel pipe scarring
The inner and outer surfaces of the steel pipe are not cleared in time due to defects such as folding and warping. In the subsequent processing, thin flakes that cannot be separated from the metal matrix are formed. Some of them are in blocks and discontinuous, rooted or not rooted on the tube wall, but cannot be peeled off naturally, which is called scarring. Surface defects must be checked and removed in time to eliminate scarring.
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