Possible problems that may be encountered in the practical application of 10 low-quality carbon steel square tubes

1. Poor dimensional accuracy. Problem description: The dimensional deviations of the outer diameter, wall thickness, diagonal length, or right angle of the square tube exceed the allowable range of national standards.. Actual impact: The inability to fit tightly during assembly, welding, or installation can result in structural framework tilting and insufficient connection strength. In severe cases, on-site cutting and correction may be required, greatly increasing construction difficulty and cost. 

2. Uneven wall thickness. Problem description: There are significant differences in wall thickness on the same cross-section or different sections of the pipe, with one side thicker and the other thinner.. Actual impact: This leads to unstable mechanical properties of the square tube, with stress concentrated on its weak side during load-bearing, greatly reducing its ability to resist bending, compression, and torsion, posing a structural safety hazard. 

3. Serious surface defects. Problem description: There is a large amount of rust, pitting, scratches, scarring, or peeling on the surface.. Actual impact: Not only does it affect aesthetics, but more importantly, these defects can become stress concentration points and corrosion initiation points, accelerating the corrosion of pipes and significantly reducing their durability and service life. Even after spraying, they are prone to rusting back from the defects. 

4. The weld quality is not qualified. Problem description: There are defects such as incomplete penetration, virtual welding, missed welding, high weld bead or undercutting at the welding point.. Actual impact: The weld seam is the weakest link in the square tube structure. Poor quality welds can greatly reduce the overall structural strength, and when subjected to loads or vibrations, they are prone to cracking or even complete fracture at the weld, causing catastrophic consequences. 

5. Insufficient material strength and toughness. Problem description: The use of inferior steel billets or improper production processes (such as ineffective stress relief annealing after cold bending) can result in the yield strength and tensile strength of the square tube not meeting standards, or excessive brittleness.. Actual impact: The pipe fittings cannot meet the design load-bearing requirements and are prone to permanent deformation (bending) or sudden brittle fracture when impacted, rather than receiving plastic deformation warning first, which is extremely dangerous. 

6. There is a large deviation in chemical composition. Problem description: The content of carbon (C), manganese (Mn), sulfur (S), phosphorus (P) and other elements in the steel does not meet the standards. Especially when the content of S and P is too high.. Actual impact: Excessive S content can lead to "thermal brittleness", which can easily cause cracks in welding or high-temperature environments; Excessive P content can lead to "cold brittleness", with a sharp decrease in toughness at low temperatures and a high risk of brittle fracture. Serious impact on weldability and environmental adaptability. 

7. Excessive residual stress. Problem description: The internal stress generated during the cold bending process cannot be effectively eliminated through subsequent heat treatment (annealing).. Actual impact: During subsequent cutting, welding, or load-bearing processes, residual stresses will be released, leading to unpredictable deformation or warping of the square tube, affecting structural accuracy and stability. It also makes it more prone to stress corrosion cracking. 

8. Poor corrosion resistance. Problem description: The material itself is not corrosion-resistant, and the surface treatment (such as galvanizing) layer is uneven in thickness, with poor adhesion and missing plating.. Actual impact: In corrosive environments such as humidity, acidity, and alkalinity, it will quickly rust, the bearing section will continuously decrease, the bearing capacity will rapidly decline, the service life will be much shorter than expected, and the maintenance cost will be high. 

9. Poor straightness (flatness). Problem description: The square tube is bent or twisted along its length, not a straight line.. Actual impact: It seriously affects the appearance and installation, especially when used for door and window frames, guardrails, and large steel structure skeletons. It cannot be aligned and installed, forcing the construction party to straighten or replace, which is time-consuming and laborious. 

10. Poor overall consistency. Problem description: There are significant differences in performance, size, and appearance among different parts of the same batch or even the same square tube.. Actual impact: It brings great difficulties to engineering design, quality control, and construction acceptance. The inability to reliably predict and ensure the performance of materials results in significant uncertainty in the quality and safety of the entire project.