Seamless pipes have hollow cross-sections and are used in large quantities as pipes for transporting fluids, such as pipes for transporting oil, natural gas, gas, water, and certain solid materials. Compared with welded steel pipes, seamless pipes are lighter in weight when they have the same bending and torsional strength, and are an economical section steel. Seamless pipes are widely used in the manufacture of structural parts and mechanical parts, such as octg pipes, automobile drive shafts, bicycle frames, and steel scaffolds used in building construction, etc. Steel pipes are used to make ring parts.
Internal organizational defects in seamless steel tube structures can arise during the manufacturing process and can impact the mechanical properties and integrity of the tubes. Some common internal defects include:
1.Inclusions: These are non-metallic particles or impurities present in the steel matrix. Inclusions can weaken the material and reduce its resistance to fracture and fatigue. They can be caused by inadequate refining or improper control of the steelmaking process.
2.Segregation: Uneven distribution of alloying elements or impurities within the steel can lead to local variations in mechanical properties. This can result in weak zones within the seamless tube structure, making it more susceptible to failure.
3.Weld defects: Seamless tubes are typically produced without welding. However, in some cases, defects can occur during the welding process if tubes are joined together or repaired. Weld defects such as porosity, cracks, or incomplete fusion can compromise the structural integrity of the seamless tube.
4.Grain boundary cracking: Grain boundaries are the interfaces between individual grains in the steel structure. Cracks can form along these boundaries due to various factors such as thermal stresses, hydrogen embrittlement, or improper heat treatment. Grain boundary cracking can lead to structural weakness and susceptibility to fracture.
5.Residual stress: During the manufacturing process, residual stresses can develop within the seamless steel tube structure. These stresses may arise from non-uniform cooling, deformation processes, or thermal gradients. Excessive residual stresses can increase the likelihood of distortion, deformation, or failure under certain loading conditions.
6.Internal voids: Voids or cavities within the steel structure can be introduced during the manufacturing process or as a result of inadequate material compaction. These internal voids can act as stress concentrators and reduce the strength and ductility of the seamless tube.
To mitigate these internal organizational defects, stringent quality control measures should be implemented during the steelmaking, casting, and tube manufacturing processes. Advanced inspection techniques such as ultrasonic testing, radiography, and eddy current testing can be employed to detect and assess these defects. Additionally, proper heat treatment, material selection, and process optimization can help minimize the occurrence of these defects and enhance the overall quality of seamless steel tubes.
Porosity, bubbles, shrinkage cavity residues, non-metallic inclusions, segregation, white spots, cracks and various abnormal fracture defects in cold drawn seamless steel pipes can be found through macroscopic inspection.
The method of macro inspection is divided into two methods: acid leaching inspection and fracture inspection.
A brief introduction to the common macro defects displayed by the acid leaching method is as follows:Causes of segregation: During the pouring and solidification process, the selective crystallization and diffusion caused the aggregation of certain elements, resulting in uneven chemical composition.
According to the different positions of the distribution, it can be divided into ingot type, center and spot segregation.Macroscopic characteristics: On acid-leached samples, when the segregation is erodible substances or gas inclusions, it is dark in color, irregular in shape, slightly concave, flat at the bottom and many dense microporous spots.
If the anti-corrosion element is gathered, it will be slightly convex spots with light color, irregular shape and relatively smooth.Causes of porosity: During the solidification process of the steel, the low melting point material finally solidifies and shrinks and emits gas to produce voids, but fails to be welded during the hot working process.
According to its distribution, it can be divided into two types: center and general loose.Macroscopic features: On the lateral hot acid immersion surface, the pores are irregular polygons and narrow pits at the bottom.
