Eight major defect characteristics and causes of seamless steel pipes

Eight major defect characteristics and causes of seamless steel pipes 1. Folding of seamless steel pipes It is a state that exists on the outer or inner surface of seamless steel pipes in a straight or spiral shape, continuous or discontinuous. The main reason for the 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 folds appear after drawing after extension. 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. Cracks in seamless steel pipes Refers to fine cracks distributed in straight lines or spirals on the inner and outer surfaces of seamless steel pipes, with a depth of 1 mm or more, which are continuous and discontinuous. The causes are: there are subcutaneous bubbles and subcutaneous inclusions in the hot-rolled tube blanks, cracks or deeper pits on the steel pipes before drawing, and longitudinal scratches or abrasions generated during hot rolling or cold drawing. Preventing the formation of cracks also lies in improving the quality of the tube blanks and strengthening the inspection and grinding of the tube materials. At the same time, pitting, scratches, and abrasions should be avoided during the cold drawing process. 3. Seamless steel pipe scratches The defect is characterized by longitudinal straight 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 scratches (scratches) are: there are internal scratches on the pipe material, which are not eliminated during drawing, iron oxide scale remains 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 hammerhead is bad, and the sharp edges of the transition part of the hammerhead damage the mold, etc. To prevent scratches and abrasions, the quality of each preparation 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 of which are periodic and some are irregular. The pits are caused by the iron oxide scale or other hard dirt being pressed into the steel pipe surface during the drawing or straightening process, or the peeling of the warping scale on the steel pipe surface. 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 steel pipe surface. 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 rubs against the convex shoulder of the straightening roller edge during straightening, the straightening roller has worn grooves, and the two ends of the steel pipe are bent too much, which may cause pits on the outer surface of the steel pipe. 5. Seamless steel pipe pockmarked surface Its characteristics are small pits in sheets and dots on the surface of the steel pipe. The main reason for the formation of pitting is pitting during pickling, and the excessive thickness of the iron oxide scale after annealing is straightened and pressed into the surface of the steel pipe 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 spots are removed. 6. Seamless steel pipe spots Since the seamless steel pipe is not promptly treated (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. If the contact time with water is long, or the water contains corrosive substances, rust spots will be formed. 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 sheets on the inner and outer surfaces of the seamless steel pipe that are partially separated from the metal matrix. Some of them are in blocks and discontinuous, rooted or not rooted on the pipe wall, but cannot be peeled off naturally. The causes include poor steel quality, subcutaneous bubbles, which are exposed after cold drawing; the warping produced during hot rolling is not removed from the tube blank until cold drawing; and the original deep and angular transverse pits on the steel pipe form warping after drawing. 8. Scarring of seamless steel pipe The inner and outer surfaces of the steel pipe are not cleaned in time due to defects such as folding and warping. In the subsequent processing, thin sheets that cannot be separated from the metal matrix are formed. Some of them are in blocks and discontinuous. They may or may not take root 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. Post time: Oct-14-2024