Defects And Causes of Seamless Steel Pipes

Seamless steel pipe, as an indispensable material in the modern industrial field, have a vital impact on the safety and stability of various engineering projects due to their quality and performance. However, various defects often occur during the production and use of seamless steel pipes. These defects not only affect the performance of the steel pipes, but may also threaten the safety of engineering projects. Therefore, understanding the defect characteristics and causes of seamless steel pipes is of great significance for improving the quality and use of seamless steel pipes.

Main defects of seamless steel pipes

1. Cracks

Cracks are one of the most common defects of seamless steel pipes, which manifest as straight or spiral cracks on the inner and outer surfaces of the steel pipe. The two ends and bottom of the cracks are often sharp and may be distributed in a mesh. There are many reasons for the occurrence of cracks, mainly including poor steel quality, improper heating of the pipe blank, and excessive deformation pressure.

2. Hair-like fine lines

Hairline is a continuous or discontinuous hair-like fine line on the outer surface of the seamless steel pipe, mostly spiral, and the spiral direction is opposite to the rotation direction of the puncher. The causes of hairline are similar to those of cracks, mainly related to factors such as poor steel quality and incomplete cleaning of the tube surface.

3. Internal folding

Internal folding refers to the straight or spiral serrated defects on the inner surface of the steel pipe. For high-alloy steel pipes, this defect may appear in irregular blocks and be distributed at the inlet. The main causes of internal folding include excessive front pressure of the plug, severe wear of the plug, and strong alternating stress on the metal in the center of the billet during the piercing process.

4. External folding

External folding is manifested as spiral folding on the outer surface of the seamless steel pipe, and its spiral direction is opposite to the spiral direction of the rough pipe on the piercing machine. The main causes of external folding include defects such as cracks or ears remaining on the surface of the tube billet, poor steel quality, etc.

5. Rolling folding

Rolling folding is a regular folding defect on the outer surface of the seamless steel pipe, which is mainly caused by damage to the piercing machine roll or the tube rolling mill roll.

6. Tie-off

Tie-off is the bending caused by metal entering the gap between the rollers or the loss of stability of the tube during rolling. After sizing, it appears as local convex and concave wrinkles on the surface of the steel tube. The main reasons include that the outlet diameter of the sizing machine is larger than the hole type of the sizing machine, incorrect adjustment, and roller misalignment.

Causes of seamless steel pipe defects

1. Raw materials

Poor internal structure and poor surface quality of raw materials are important causes of seamless steel pipe defects. Poor internal structure may cause defects such as internal folding, internal cracks in the tube wall, and delamination; poor surface quality may cause defects such as external folding.

2. Process operation

Improper process operation such as improper heating, excessive deformation pressure, and incomplete cleaning of the tube surface are also important causes of seamless steel pipe defects. Improper heating may cause defects such as internal folding, external folding, and internal cracks in the tube wall; excessive deformation pressure may cause defects such as cracks.

3. Equipment

Poor equipment performance, looseness, and scratches may also cause seamless steel pipe defects. For example, damage to the piercing machine roll or the tube mill roll may lead to defects such as rolling folding.

Prevention and control of seamless steel pipe defects

In order to reduce the occurrence of seamless steel pipe defects and improve the quality and use effect of seamless steel pipes, the following measures need to be taken:

1. Strengthen raw material quality control

Strictly control the internal organization and surface quality of raw materials, and select high-quality raw materials for production.

2. Optimize process operation

Reasonably set process parameters such as heating temperature and deformation pressure to ensure the stability and accuracy of process operation. At the same time, strengthen the surface cleaning of the tube billet to ensure the smoothness and flatness of the tube billet surface.

3. Strengthen equipment maintenance and management

Regularly inspect and maintain production equipment to ensure the normal operation and stable performance of the equipment. Damaged equipment parts should be replaced and repaired in time to avoid equipment failures affecting the quality of seamless steel pipes.

4. Strengthen quality inspection and monitoring

Establish a complete quality inspection and monitoring system to monitor and inspect the production process of seamless steel pipes throughout the process. Defects found should be handled and rectified in a timely manner to ensure that the quality of seamless steel pipes meets the standard requirements.

Summary

In summary, the defect characteristics and causes of seamless steel pipes are multifaceted, and comprehensive analysis and control are required from the aspects of raw materials, process operation, equipment, etc. By strengthening raw material quality control, optimizing process operation, strengthening equipment maintenance and management, and strengthening quality inspection and monitoring, the generation of seamless steel pipe defects can be effectively reduced and the quality and use effect of seamless steel pipes can be improved.

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