What are the methods for identifying counterfeit and substandard thick-walled seamless steel pipes

1. Counterfeit and substandard thick-walled seamless steel pipes are prone to folding. Folding refers to various fold lines forming on the surface of thick-walled seamless steel pipes. This defect often runs the entire length of the product. The reason for folding is that substandard manufacturers pursue high efficiency, resulting in excessive reduction in rolling weight, creating "ears." These folds then cause folding during the next rolling process. Folded products will crack after bending, significantly reducing the strength of the thick-walled seamless steel pipe.

2. Counterfeit and substandard thick-walled seamless steel pipes often have a pitted surface. This pitting is caused by severe wear of the rolling grooves, resulting in irregular unevenness on the surface of the thick-walled seamless steel pipe. Because manufacturers of substandard thick-walled seamless steel pipes prioritize profits, they often exceed the rolling weight limits.

3. Counterfeit and substandard thick-walled seamless steel pipes are prone to developing scale on their surface. There are two reasons for this: 1) The material of counterfeit and substandard thick-walled seamless steel pipes is uneven, containing many impurities. 2) Substandard manufacturers use rudimentary guide equipment, which easily causes steel to stick. These impurities, after biting into the rolls, easily form scale.

4. Inferior materials are prone to surface cracks because their billets are made of clay. Clay billets have many pores, and during the cooling process, they are subjected to thermal stress, causing cracks that appear after rolling.

5. Inferior thick-walled seamless steel pipes are easily scratched because manufacturers of inferior materials use rudimentary equipment, which easily produces burrs that scratch the surface of the thick-walled seamless steel pipes. Deep scratches reduce the strength of the thick-walled seamless steel pipes.

6. Inferior thick-walled seamless steel pipes lack metallic luster and appear pale red or similar to pig iron. There are two reasons for this: 1) Their billets are made of clay. 2) The rolling temperature of inferior materials is not standardized; their steel temperature is determined visually, making it impossible to roll within the specified austenitic region, thus the performance of the thick-walled seamless steel pipes cannot meet the standards.

7. Inferior thick-walled seamless steel pipes often have thin and low transverse ribs, frequently resulting in incomplete filling. This is because manufacturers, to achieve large negative tolerances, excessively reduce the material in the first few passes of finishing, resulting in smaller molds and incomplete filling of the die.

8. Inferior thick-walled seamless steel pipes have an elliptical cross-section. This is because manufacturers, to save material, excessively reduce the material in the first two passes of finishing. This significantly reduces the strength of the rebar and does not conform to the standard dimensions of rebar.

9. High-quality thick-walled seamless steel pipes have uniform composition, are produced by high-tonnage cold shearing machines, and have smooth and neat cut ends. Inferior materials, due to their poor quality, often exhibit unevenness and lack of metallic luster at the cut ends. Furthermore, because manufacturers of inferior materials cut fewer ends, large burrs may appear at the beginning and end.

10. Inferior thick-walled seamless steel pipes contain more impurities, have lower steel density, and severely deviate from dimensional tolerances. Therefore, in the absence of calipers, they can be weighed for verification. For example, for 20mm rebar, the national standard stipulates a negative tolerance of 5%. When the length is 9m, its theoretical weight per piece is 120 kg. Its minimum weight should be: 120 x (1 - 5%) = 114 kg. If the actual weight of a single piece is less than 114 kg, it is a substandard thick-walled seamless steel pipe because its negative tolerance exceeds 5%. Generally, weighing the entire length is more effective, mainly considering cumulative error and probability.

11. Substandard thick-walled seamless steel pipes have large fluctuations in inner diameter due to: 1) unstable steel temperature with uneven heating/cooling. 2) uneven steel composition. 3) Due to rudimentary equipment, low foundation strength, and large mill bounce, there can be significant changes in inner diameter within the same cycle. Such uneven stress on the rebar makes it prone to breakage.

12. High-quality materials have more standardized trademarks and markings.

13. For thick-walled seamless steel pipes with diameters of 16mm or more, the spacing between the two trademarks is more than 1m.

14. The longitudinal ribs of substandard thick-walled seamless steel pipes with threaded bars are often wavy.