Inspection Standards for Square Tube Surface Quality

1. **Grain Structure:**

- The grain structure of the tube should be uniform and free from any abnormalities. The size of the grains should be within the specified range, indicating a properly heat-treated and rolled material.

2. **Surface Defects:**

- The surface of the square tube should be free from any visible defects such as scrapes, scratches, dents, or gouges. These can compromise the structural integrity of the tube or interfere with the function of the tube in a particular application.

3. **Roughness:**

- The surface roughness of the tube should be within an acceptable range. Excessive roughness can affect the flow characteristics of fluids inside the tube or impact the performance of the tube in a friction-sensitive application.

4. **Ovalization:**

- The square tube should have a uniform cross-section without any significant ovalization. Ovalization can affect the strength and functionality of the tube.

5. **Welding Flaws:**

- If the square tubes are welded, the welds should be inspected for any flaws such as裂纹 (cracks), porosity, or undercut. These flaws can weaken the structure of the tube and compromise its integrity.

6. **Chemical Stains or Discoloration:**

- The surface of the tube should be free from any chemical stains or discoloration that may be caused by improper manufacturing processes or exposure to contaminants.

7. **Dimensional Tolerances:**

- The dimensions of the square tube, including its width, height, and wall thickness, should be within the specified tolerances. Dimensional accuracy is important for the tube to fit properly in its intended application.

8. **Compliance with Standards:**

- The surface quality inspection should be conducted in accordance with relevant international and national standards, such as ASTM, ASME, EN, JIS, or GB standards, depending on the location and application of the tubes.