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Home >News >Industry News >How to Prevent the Defects of Pipes?
How to Prevent the Defects of Pipes?
Posted: 05/09/2022 19:22:24  Hits: 18
 
Perforation is the first process and one of the most important deformation processes of hot rolled seamless steel pipes. Its function is to pierce the solid tube blank and a hollow tube is formed. According to the deformation characteristics of the tube blank's piercing process, it is divided into the longitudinal rolling piercing and cross rolling piercing. Defects may occur for both of them.
 
Defects occur due to the heating process or defects of the tube blank, and the defect further expands after the tube blank is perforated. Defects also happen in the perforation process, which are caused by incorrect design or adjustment of perforation process parameters, unreasonable shapes of the perforation tool, and defects on the surface of the perforation tool.
 
Different perforated machines and different perforated methods will result in different reasons for the defects of the tube blank. The defects of perforated tube blank mainly include uneven wall thickness, surface scars, scratches, inward folds, outward folds and delaminations of the tube blank.
 
Defects and prevention in longitudinal rolling piercing processes
Longitudinal rolling piercing includes pressure piercing and push rolling piercing. The defects brought about by this piercing process are related to the inherent defects of the process, the quality of piercing tools and improper operation, mainly including nonuniform wall thickness of the hole blank and scratches on the surface.
 
The uneven wall thickness of pierced hole blank: One of the main reasons is that the piercing process is easy to cause the centerline of the piercing rod to deviate from the centerline of the tube blank, so that the piercing inner hole of the hole blank is eccentric; the other is that the punch connecting the punch head will bend under the action of the great piercing force (back thrust), and its tail end will also be bent.
 
Preventive measures:
A. Ensure that the tube blank is heated evenly to prevent serious burning loss to eliminate uneven wall thickness of piercing holes due to the poor heating of the tube blank.
B. Make the centerline of the tube blank to coincide with the centerline of the punches much as possible.
C. Prevent the bending of the punch. If it is bent, it should be replaced in time.
 
Cross rolling piercing processes and defects and their prevention
The cross-rolling piercing process is the most widely used in the production of seamless steel pipes, which was invented by the Mannesmann brothers in Germany in 1883. The cross rolling piercing machine includes two-roller type cross rolling piercing machines and three-roller type cross rolling piercing machines. The defects of the tube blank produced by the cross rolling mainly include the inward folding, the outward folding, the uneven wall thickness and the surface scratches of the tube blank.
 
Inward folding of tube blanks: defects easily occur for the tube blank in cross-rolling piercing, which is closely related to the piercing performance of the tube blank, the adjustment of the piercing process parameters of the piercing pass machine and the quality of the piercing head. The factors affecting the inward folding of the tube blank are: first, the amount of compression and the number of compressions before the piercing head, second, the shape of the hole, and third, the surface quality of the piercing head.
 
Outward folding of tube blanks: the outward folding of tube blanks is mostly caused by the surface defect of the tube blank, which is another surface defect that is easily caused when the tube blank is cross-rolled and pierced. Factors affecting the outward folding of the tube blank:
A. The plasticity of the tube blank and the deformation of the perforation
B. The surface defect of the tube blank
C. The quality of the perforation tool and the shape of the hole
 
Uneven thickness of the tube blank's wall: There is uneven wall thickness in transverse and longitudinal directions, and uneven thickness in the transverse direction is most likely to occur during cross-rolling and piercing. The main factors that affect the uneven transverse wall thickness of the tube blank are the heating temperature of the tube blank, the centering of the tube end, the hole type adjustment of the piercing machine, and the shape of the tool.
 
Scratches on the surface of the tube blank: Although the requirements for the surface quality of the perforated tube blank are not as strict as that for the surface quality of the steel pipe by the rolling mill and the sizing machine, the serious surface scratches of the tube blank will also affect the surface quality of the steel pipe. Factors affecting the surface scratches of the tube blank: the main reasons are that the surface of the perforating tool or the roller table at the exit of the perforator is severely worn, not smooth or the roller table does not rotate. To prevent scratches on the surface of the tube blank due to the surface defects of the piercing tools, the inspection and grinding of the piercing tools should be paid more attention to.
 


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Teresa
Teresa
Teresa is a skilled author specializing in industrial technical articles with over eight years of experience. She has a deep understanding of manufacturing processes, material science, and technological advancements. Her work includes detailed analyses, process optimization techniques, and quality control methods that aim to enhance production efficiency and product quality across various industries. Teresa's articles are well-researched, clear, and informative, making complex industrial concepts accessible to professionals and stakeholders.
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