1. Fake and inferior
thick-walled steel pipes are prone to folding. Folds are various fold lines formed on the surface of
thick-walled steel pipes, and this defect often runs through the longitudinal direction of the entire product. The reason for the folds is that the counterfeit and inferior manufacturers pursue the rate, the reduction amount is too large, and the ears are formed. Folding occurs during the next rolling, and the folded product will crack after being bent, and the strength of the steel will be greatly reduced.
2. The appearance of fake and inferior
thick-walled steel pipes often has a pockmarked surface. The pitted surface is the irregular unevenness on the surface of the steel due to the serious wear of the rolling groove. Due to the pursuit of profit by manufacturers of fake and inferior
thick-walled steel pipes, groove rolling often exceeds the standard.
3. The surface of the fake and inferior
thick-walled steel pipe is prone to scarring. There are two reasons: (1). The material of fake and inferior steel pipes is uneven and there are many impurities. (2). The guide and guard equipment of the fake and inferior material manufacturers are simple and easy to stick to the steel. These impurities are prone to scarring after biting the roll.
4. The surface of the fake and inferior material is prone to cracks. The reason is that its blank is adobe, and the adobe has many pores. During the cooling process, the adobe is subjected to thermal stress, resulting in cracks. After rolling, there are cracks.
5. Fake and inferior
thick-walled steel pipes are easy to be scratched because the fake and inferior
thick-walled steel pipe manufacturers have simple equipment, which is easy to produce burrs and scratch the surface of the steel. Deep scratches reduce the strength of the steel.
6. The fake and inferior
thick-walled steel pipe has no metallic luster and is light red or similar to pig iron. There are two reasons for this. Its blank is adobe. 2. The rolling temperature of counterfeit and inferior materials is not standard, and their steel temperature is measured visually so that the rolling cannot be carried out according to the specified austenite area, and the performance of the steel will naturally fail to meet the standard.
7. The transverse bars of the fake and inferior
thick-walled steel pipes are thin and low, and the phenomenon of unsatisfactory filling often occurs. The reason is that to achieve a large negative tolerance, the reduction amount of the first few passes of the finished product is too large, the iron shape is too small, and the hole shape is unsatisfactory.
8. The cross-section of the fake and inferior
thick-walled steel pipe is oval. The reason is that to save materials, the reduction amount of the first two passes of the finished roll is too large. standard.
9. The composition of the steel is uniform, the tonnage of the cold shearing machine is high, and the end face of the cutting head is smooth and tidy. However, due to the poor material of the counterfeit material, the end face of the cutting head often has the phenomenon of falling meat, that is, unevenness and no metallic luster. And because the products of the fake and inferior material manufacturers have fewer cutting heads, there will be big ears at the head and tail.
10. The material of the fake and inferior
thick-walled steel pipe contains a lot of impurities, the density of the steel is too small, and the size is 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, its single theoretical weight is 120 kg, and its minimum weight should be: 120X (l-5%) = 114 kg, called If the actual weight of a single piece is less than 114 kg, it is fake and inferior steel, because its negative tolerance exceeds 5%. Generally speaking, the effect of whole phase weighing will be good, mainly considering the problem of cumulative error and probability theory.
11. The inner diameter of the fake and inferior
thick-walled steel pipe fluctuates greatly, because:
① The steel temperature is unstable and there are yin and yang sides. ②, the composition of steel is not uniform. ③. Due to the simple equipment and low foundation strength, the rolling mill bounces greatly. There will be a large change in the inner diameter within the same week, and the uneven stress of such a steel bar is prone to fracture.
12. The trademark and printing of the tube are relatively standardized.
13. For large threads with a diameter of more than 16 steel pipes, the spacing between the two trademarks is above IM.
14. The longitudinal bars of the fake and inferior steel rebar is often wavy.
15. Fake and inferior
thick-walled steel pipe manufacturers are loosely packed because they do not have traffic. The sides are oval.
Welded steel pipe process:
Uncoiling - Flattening - End cutting and welding - Looper - Forming - Welding - Removal of internal and external welding beads - Pre-calibration - Induction heat treatment - Sizing and straightening - Eddy current testing - Cutting off ——Water pressure inspection——Pickling——Final inspection——Packing
