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Hebei Hengtong Pipe Fittings Group Co., Ltd.

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How to assess the quality of steel pipes

Summary Description： Here’s what you need to know about methods for identifying the quality of steel pipe products.

1. Low-quality steel pipes are prone to bending.

Folds are various crease lines that form on the surface of steel pipes; this defect often runs along the entire longitudinal side of the product. The cause of folding is that substandard manufacturers, in pursuit of high efficiency, apply excessive rolling pressure, resulting in “ears” that fold during the next rolling pass. After folding, the product may crack when bent, and its strength will be reduced.

2. The surface of low-quality steel pipes is often pitted.

Pitted surfaces are irregular, uneven defects on the steel surface caused by severe groove‑type wear. Due to cost‑cutting practices, substandard pipe manufacturers often engage in excessive bevel rolling.

3. Low-quality steel pipes are prone to surface scabbing.

There are two reasons: (1) The material of substandard steel pipes is uneven and contains numerous impurities. (2) Manufacturers using inferior materials often employ rudimentary guide‑rail equipment, which can lead to steel sticking; these impurities, when caught in the rolls, readily cause surface defects.

4. The surface of low-quality materials is prone to cracking because their blanks are made of mud bricks, which have high porosity; during cooling, the mud bricks…

Cracks are generated due to thermal stresses during the process, and they also appear after rolling.

5. Low-quality steel pipes are prone to scratching because manufacturers of substandard pipes use rudimentary equipment, which easily leaves burrs and damages the steel surface. Deep scratches can reduce the steel’s strength.

6. Fake steel pipes lack metallic luster and exhibit a pale red hue or a color resembling pig iron; this is due to two factors. 2. The rolling temperature of substandard materials is not properly controlled—steel temperatures are judged by eye, preventing proper rolling within the prescribed austenitic range, which in turn results in steel properties that fail to meet specifications.

7. Poorly manufactured steel pipes exhibit thin, low‑profile cross‑bars and frequent underfilling, as manufacturers, in pursuit of tighter negative tolerances, apply excessive pressure during the initial forming stages, resulting in an overly small pipe profile and an unsatisfactory final shape.

8. The cross-section of substandard steel pipes is elliptical because, in an effort to save materials, the manufacturer applies excessive pressure during the first two rolling passes. This results in a significant reduction in the steel’s strength and failure to meet the standard specifications for external dimensions.

9. High-quality steel has a uniform composition, and the cold‑shear machine boasts high tonnage, resulting in smooth, neat cut‑end faces. In contrast, inferior products often exhibit uneven cut‑end surfaces with no metallic luster, and due to the use of substandard materials, the manufacturer produces fewer cut ends, leading to pronounced “big ears” at both the head and tail.

10. Fake steel pipe material often contains numerous impurities, has a lower steel density, and exhibits significant dimensional deviations; it can be verified by weighing without the need for a vernier caliper. For example, consider rebar No. 20: according to national standards, the maximum negative tolerance is 5%. If the theoretical weight of a single bar is 120 kg and its length is 9 m, the minimum allowable weight should be: 120 × (1 − 5%) = 114 kg. If the actual measured weight of an individual bar is less than 114 kg, then that bar is substandard steel, as its negative tolerance exceeds 5%. In general, it is preferable to use integral proportioning, primarily taking into account cumulative errors and probabilistic considerations.

11. The inner diameter of substandard steel pipes fluctuates significantly, due to the following reasons: 1) unstable steel temperature with uneven heating; 2) non-uniform chemical composition; and 3) inadequate equipment and low foundation strength, leading to mill vibration. Consequently, the pipe’s dimensions vary considerably within a single week, resulting in uneven stress distribution and increased susceptibility to fracture.

12. The quality of logos and printing is relatively standardized.

13. Three steel pipes with diameters greater than 16 have large threads, and the spacing between any two trademarks is at least 1 meter.

14. The longitudinal reinforcement bars of substandard steel often exhibit a wavy profile.

15. Due to the lack of production, substandard steel pipe manufacturers often use loose packaging, and the cross-section is oval-shaped.

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Cleaning Knowledge for Forged Flanges

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