Differentiate high-quality seamless steel pipes from low-quality seamless steel pipes with the naked eye

First, the surface of low-quality seamless steel pipes is prone to scarring.
This is mainly caused by two reasons:
(1) Low-quality seamless steel pipes have more impurities and uneven materials.
(2) The guide equipment of low-quality pipe manufacturers is simple and is particularly easy to stick to steel. Pipes containing impurities are prone to scarring after biting into the rollers.

Second, low-quality seamless steel pipes are prone to pipe folding.
The so-called folding refers to various fold lines formed on the surface of seamless steel pipes. This defect often runs through the entire longitudinal direction of the product. The reason for the folding is that to increase production and pursue high efficiency, the manufacturer presses down too much during the production process, resulting in ears, which are prone to folding in the next rolling process. The folded product is prone to cracking after bending, which greatly reduces the strength of the pipe.

Third, low-quality seamless steel pipes are prone to scratching. The reason is that the production equipment of low-quality steel pipe manufacturers is simple, and the products are prone to burrs, scratching the surface of the steel. Deep scratches will reduce the strength of the steel.

Fourth, the surface of inferior seamless steel pipes often has pitting.
The pitting is the irregular unevenness of the steel surface caused by severe wear of the rolling groove. Because inferior steel pipe manufacturers want to pursue profits, the rolling groove often exceeds the standard.

Fifth, the surface of inferior pipes is prone to cracks. One of the reasons is that its blank is adobe, which has many pores. During the cooling process, due to the effect of thermal stress, cracks are generated, and after rolling, there are cracks.

Sixth, inferior seamless steel pipes have no metallic luster and are light red or similar to pig iron. There are two reasons:
(1) Its blank is adobe.
(2) The rolling temperature of inferior materials is not standard. Their steel temperature is visually measured, so it cannot be rolled according to the specified austenite area, and the performance of the steel naturally cannot meet the standard.

Seventh, the transverse ribs of inferior seamless steel pipes are thin and low and often appear to be insufficiently filled. 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 filled.

Eighth, the composition of high-quality steel is uniform, the specifications of the pipe-cutting machine are high, and the end face of the cut head is smooth and neat, while the inferior material has poor material quality, and the end face of the cut head often has the phenomenon of meat loss, that is, uneven, and no metallic luster. Moreover, due to the small number of cut heads of inferior material manufacturers, large ears will appear at the head and tail.

Ninth, the cross-section of the inferior seamless steel pipe is irregular and the ovality error is large. The reason is that to increase production, the manufacturer presses down the first two passes of the finished product roller too much, which greatly reduces the strength of this seamless steel pipe and does not meet the standard of the shape and size of the seamless steel pipe.

Tenth, the material of the inferior seamless steel pipe contains many impurities, the density of the steel is too small, 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 national standard stipulates that the maximum negative tolerance is 5%. When the fixed length is 9M, the theoretical weight of a single 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 inferior steel because its negative tolerance exceeds 5%. Generally speaking, the whole weighing effect will be better, mainly considering the cumulative error and probability theory.

Eleventh, the inner diameter size of inferior seamless 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 large changes within the same week. Such seamless steel pipes are prone to fracture due to uneven force.

Twelfth, the trademarks and printing of high-quality seamless steel pipes are relatively standardized.

Thirteenth, the inferior seamless steel pipe manufacturers are relatively loose because they do not have a crane. The side is oval.