The development of steel pipe production technology began with the rise of bicycle manufacturing, the development of oil in the early 19th century, the manufacture of ships, boilers and aircraft during the two world wars, the manufacture of thermal power boilers after the Second World War, the development of the chemical industry and Oil and gas drilling and transportation, etc., have strongly promoted the development of seamless steel tubes and electric resistance welded pipes in terms of variety, output and quality. While the steel pipe is developing rapidly, some fake steel pipe products on the market have also appeared one after another. How to correctly and accurately identify the quality of the steel pipe?
1. The appearance of fake steel pipes often has pockmarks. The pockmark is a defect caused by the irregularity of the surface of the steel due to the serious wear of the groove. Due to the pursuit of profit by shoddy steel pipe manufacturers, the most frequent rolling mill rolling is exceeded.
2. The cross section of the inferior steel pipe is elliptical. The reason is that the manufacturer has to reduce the amount of the two rolls in front of the finished roll in order to save material. The strength of the rebar is greatly reduced, and it does not meet the standard of the rebar dimensions. .
3. The composition of high-quality steel is uniform, the tonnage of the cold-shearing machine is high, the end face of the cutting head is smooth and tidy, and the fake inferior material is often poor in material, and the end face of the cutting head often has the phenomenon of falling meat, that is, unevenness and no metallic luster. And because the fake inferior products manufacturers have fewer heads, big ears will appear at the head and tail.
4. The inner diameter of the inferior steel pipe fluctuates greatly because of:
(1) The temperature of the steel is unstable and there are yin and yang faces.
(2) The composition of steel is not uniform.
(3) Due to the poor equipment and low foundation strength, the rolling mill has a large bounce. There will be a large change in the same week, and such a steel bar is unevenly stressed and easily broken.
5. the fake steel pipe material contains more impurities, the density of steel is too small, and the size is too bad, so in the absence of vernier calipers, it can be weighed and checked. For example, for rebar 20, the national standard specifies a maximum negative tolerance of 5%. At a fixed length of 9 M, its single theoretical weight is 120 kg. Its minimum weight should be: 120 X (l-5%) = 114 kg. The actual weight of a single root is less than 114 kilograms, which is a fake steel because its negative tolerance exceeds 5%. In general, the effect of the phasing weighing will be better, mainly considering the problem of cumulative error and probability theory.
6. the fake steel pipe is easy to scratch, the reason is that the equipment of the fake steel pipe manufacturers is simple, easy to produce burrs, scratching the steel surface. Deep scratches reduce the strength of the steel.
7, the surface of the fake steel pipe is prone to scarring. There are two reasons for this:
(1) The material of the fake steel pipe is uneven and has many impurities.
(2) The guide equipment of the fake inferior material manufacturer is simple and easy to stick steel. These impurities are easy to cause crusting after biting the roller.
8. The trademarks and printing of high-quality tubes are relatively standardized.
9. The longitudinal reinforcement of the counterfeit steel rebar is often wavy.