First, identification methods of fake and inferior steel pipes:
1. Fake and inferior thick-walled steel pipes are prone to folding. Folding is a variety of fold lines formed on the surface of thick-walled steel pipes. This defect often runs through the entire longitudinal direction of the product. The reason for the folding is that the fake and inferior manufacturers pursue the rate, the amount of pressing is too large, and ears are produced. Folding occurs during the next rolling. The folded product will crack after bending, and the strength of the steel will be greatly reduced.
2. The surface of fake and inferior thick-walled steel pipes often has a pockmarked surface. Pockmarking is an irregular and uneven defect on the surface of the steel caused by severe wear of the rolling groove. Because fake and inferior thick-walled steel pipe manufacturers want to pursue profits, the rolling groove often exceeds the standard.
3. The surface of fake and inferior thick-walled steel pipes is prone to scarring. There are two reasons: (1) The material of fake and inferior steel pipes is uneven and has many impurities. (2) The guide equipment of fake and inferior material manufacturers is simple and easy to stick to steel. These impurities bite the rollers and easily cause scarring.
4. The surface of fake and inferior materials is prone to cracks because its blank is adobe, which has many pores. During the cooling process, the adobe is subjected to thermal stress, resulting in cracks, and cracks after rolling.
5. Fake and inferior thick-walled steel pipes are easily scratched because the equipment of fake and inferior thick-walled steel pipe manufacturers is simple, which is easy to produce burrs and scratch the surface of steel. Deep scratches reduce the strength of steel.
6. Fake and inferior thick-walled steel pipes have no metallic luster and are light red or similar to the color of pig iron. There are two reasons. 2. Its blank is adobe. 2. The rolling temperature of fake and inferior materials is not standard. Their steel temperature is visually measured, so it is impossible to roll according to the specified austenite area, and the performance of the steel naturally cannot meet the standard.
7. The transverse ribs of fake and inferior thick-walled steel pipes are thin and low, and they often appear incomplete. The reason is that to achieve a large negative tolerance, the manufacturer presses down the first few passes of the finished product too much, the iron type is too small, and the hole type is not full.
8. The cross-section of the fake and inferior thick-walled steel pipe is oval. The reason is that to save materials, the manufacturer has a large amount of pressure before the second pass of the finished product roller. The strength of this threaded steel is greatly reduced, and it does not meet the standard of threaded steel appearance size.
9. The composition of the steel is uniform, the tonnage of the cold shear is high, and the end face of the cut head is smooth and neat. However, due to the poor material quality, the end face of the cut head of the fake and inferior material often has the phenomenon of meat loss, that is, uneven, and no metallic luster. Moreover, since the fake and inferior material manufacturer's products have few cut heads, there will be big ears at the head and tail.
10. The fake and inferior thick-walled steel pipe contains many impurities, the density of the steel is low, and the size is seriously out of tolerance, so it can be weighed and checked without a vernier caliper. For example, for rebar 20, the standard stipulates that the maximum negative tolerance is 5%. When the fixed length is 9M, the theoretical weight of a single root is 120 kg. Its minimum weight should be: 120X (l-5%) = 114 kg. If the actual weight of a single root is less than 114 kg, it is a fake and inferior steel because its negative tolerance exceeds 5%. Generally speaking, the whole phase weighing effect will be better, mainly considering the cumulative error and probability theory.
11. The inner diameter size of fake and inferior thick-walled steel pipes fluctuates greatly because:
① The steel temperature is unstable and there are positive and negative sides. ② The composition of the steel is uneven. ③ Due to the simple equipment, low foundation strength, and large bounce of the rolling mill. There will be a large change in the inner diameter within the same week, and such steel bars are prone to fracture due to uneven force.
12. The trademarks and printing of steel pipes are relatively standardized.
13. For large threads with a diameter of more than 16 in three steel pipes, the spacing between the two trademarks is above IM.
14. The longitudinal reinforcement of fake and inferior steel rebars is often wavy.
15. Since the fake thick-walled steel pipe manufacturers do not have a crane, the packaging is relatively loose. The side is oval.


Second, the process flow of welded steel pipes:
Uncoiling - flattening - end shearing and welding - looping - forming - welding - internal and external weld bead removal - pre-correction - induction heat treatment - sizing and straightening - eddy current detection - cutting - water pressure inspection - pickling - final inspection - packaging