When we inspect the quality of square and rectangular tube blanks, we can start from the following ten aspects:

(1) There shall be no cracks, scars, inclusions, folds, cracks, or ears on the surface of the square tube blank.

(2) The low-magnification structural inspection of the square and rectangular tube blanks should be carried out, and there must be no visible bubbles, white spots, cracks, skinning inclusions, and residual shrinkage cavities on the low-magnification test pieces for acid leaching.

(3) Use a measuring tool to measure along the vertical direction of the billet length at a distance of not less than 150mm from the end of the billet, and take the largest dimension as the side length value.

(4) The maximum depth of scratches, roll marks, pits, and pits allowed on the surface is 2mm when the side length is ≤140mm; 3mm when the side length is ≥200mm, and the maximum depth of hairlines allowed on the billet surface is: 1mm when ≤140mm; 2mm when side length ≥200mm.

(5) Measure the distance between the two end faces along the centerline of the side of the rectangular tube blank as the actual length.

(6) There shall be no shrinkage cavity, airbag, delamination, and tail hole on the end face of the tube blank.

(7) Batch inspection and acceptance shall be carried out. Gland steel billets shall be batched by-products of the same brand and cross-sectional size; killed steel billets shall be batched by-products of the same brand, same furnace number, and same cross-sectional size.

(8) The size and shape of the tube blanks should be measured one by one with suitable measuring tools.

(9) Surface defects of square and rectangular tube blanks are allowed to be removed. The cleaning place should be smooth without edges and corners, the slope after cleaning the corners should be below 45°, the cleaning depth should not be greater than 10% of the side length, and the cleaning width should not be less than five times the cleaning depth.

(10) If a certain test result does not meet the standard requirements, double samples can be taken from the same batch for re-inspection of the unqualified item. If the re-inspection result is unqualified, the whole batch shall not be delivered.