GB/T 4436-2026Tolerances on form and dimensions of wrought aluminium and aluminium alloy tubes (English PDF)

5.1.1 Outer diameter

5.1.1.1 When the pipe wall thickness is greater than 2.5% of the outer diameter, the outer diameter deviation of the extruded seamless round pipe shall conform to the provisions of Table

6.The buyer requires high precision. If so, it should be noted in the order form; otherwise, it will be supplied as ordinary grade.

5.1.3 Curvature Except for the O condition, the curvature of extruded seamless round tubes should conform to the specifications in Table

8.If the buyer requires high-precision or ultra-high-precision grades, this should be specified when ordering. If specified in the order, otherwise supplied as standard grade. The buyer may specify the curvature of the O-state extruded seamless round tube or other states of extruded seamless round tubes. When there are special requirements for the degree of curvature, the supplier and the buyer shall negotiate and determine the degree of curvature and specify it in the order form.

5.1.4 Length

5.1.4.1 The length of extruded seamless round tubes supplied in irregular lengths shall not be less than 300mm.

5.1.4.2 The length deviation of extruded seamless round tubes supplied in fixed lengths (or multiple lengths) shall conform to the provisions of Table

9.When the buyer requires high precision, this should be specified in the order. If the bill of lading does not specify otherwise, the goods will be supplied as standard grade. For pipes supplied in multiples of length, a 5mm allowance should be left for each cut.

5.1.5 Cutting slope The bevel angle of extruded seamless round tubes should conform to the specifications in Table

10.If the buyer requires high precision, this should be specified in the purchase order; otherwise, it should be calculated according to... Standard grade supply.

5.2.1 Outer diameter

5.2.1.1 When the wall thickness of the extruded seamed round tube is greater than 2.5% of the outer diameter, its outer diameter deviation shall conform to the provisions of Table 11.

5.2.1.2 When the wall thickness of an extruded welded round tube is not greater than 2.5% of its outer diameter, the permissible deviation of its outer diameter shall meet the following requirements.

a) When the ratio of wall thickness to outer diameter is >0.5%~1.0%, the allowable deviation is 4 times the corresponding value in Table 11;

b) When the ratio of wall thickness to outer diameter is >1.0%~1.5%, the allowable deviation is 3 times the corresponding value in Table 11;

c) When the ratio of wall thickness to outer diameter is >1.5%~2.0%, the allowable deviation is twice the corresponding value in Table 11;

d) When the ratio of wall thickness to outer diameter is >2.0%~2.5%, the allowable deviation is

1.5 times the corresponding value in Table 11.

5.2.2 Wall thickness The wall thickness deviation of extruded seamed round tubes should conform to the specifications in Table

12.If the buyer requires high precision, this should be specified in the purchase order; otherwise, it should be noted. Supply at the standard grade.

5.2.4 Length

5.2.4.1 The length of extruded seamless round tubes supplied in irregular lengths shall not be less than 300mm.

5.2.4.2 The length deviation of extruded seamless round tubes supplied in fixed lengths (or multiple lengths) shall conform to the provisions of Table

14.When the buyer requires high precision, this should be specified in the order. If the bill of lading does not specify otherwise, the product will be supplied as standard grade. For pipes supplied in multiples of length, a 5mm allowance should be left for each cut.

5.2.5 Cutting slope The bevel of the extruded seamed round tube should conform to the specifications in Table

15.If the buyer requires high precision, this should be specified in the purchase order; otherwise, it should be calculated according to... Standard grade supply.

5.3.3 Curvature Except for O-state tubing, extruded welded square tubing, flat tubing, hexagonal tubing, and octagonal tubing with a wall thickness not less than 1.5% of the circumscribed circle diameter are permitted in any... The curvature over a 300mm length should not exceed 0.6mm, and the average curvature per meter of the entire length should not exceed 1.5mm. The curvature of extruded seamed square tubes, flat tubes, hexagonal tubes, and octagonal tubes in the O state or with a wall thickness less than 1.5% of the circumscribed circle diameter is important. If there are special requirements for the curvature, the supplier and the buyer shall negotiate and determine the specific requirements, and indicate them in the order form.

5.3.4 Planar clearance The planar clearance of extruded seamed square tubes, flat tubes, hexagonal tubes, and octagonal tubes should conform to the specifications in Table

18.When the buyer requires high precision, this should be specified in the order. If the invoice specifies otherwise, the goods will be supplied as standard grade.

5.3.5 Torque The torsion tolerances of extruded seamed square tubes, flat tubes, hexagonal tubes, and octagonal tubes should conform to the specifications in Table

19.If the buyer requires high precision, this should be specified when ordering. If the order form specifies otherwise, the goods will be supplied as standard grade.

5.3.6.2 The angular deviation of extruded seamed hexagonal and octagonal tubes shall not exceed 3 times the allowable deviation value of the side length for ordinary grade, and shall not exceed [a certain value] for high-precision grade. Permissible deviation value for side length. If the buyer requires high precision, it should be specified in the purchase order; otherwise, it will be supplied as ordinary precision.

5.3.7 Corner radius (or chamfer radius)

5.3.7.1 For extruded seam square tubes, flat tubes, hexagonal tubes, and octagonal tubes where the fillet radius (or chamfer radius) is not specified at the sharp corners, allowances are made for the sharp corners. The fillet should be rounded to make it smooth, and the fillet radius (or chamfer radius) should conform to the specifications in Table

21.If the buyer requires high precision, this should be specified in the drawings or order. If specified in the order, otherwise supplied as standard grade. If the buyer has special requirements for fillet radius or chamfer radius, these shall be negotiated between the supplier and the buyer and stipulated in the order. Please indicate this in the drawings or order form.

5.3.7.2 The deviation of the fillet radius (or chamfer radius) of extruded seamed square tubes, flat tubes, hexagonal tubes and octagonal tubes shall conform to the provisions of Table 22.

5.3.8 Length

5.3.8.1 The length of extruded seam square tubes, flat tubes, hexagonal tubes and octagonal tubes supplied in irregular lengths shall not be less than 300mm.

5.3.8.2 The length deviation of extruded seamed square tubes, flat tubes, hexagonal tubes, and octagonal tubes supplied in fixed lengths (or multiple lengths) shall conform to the provisions of Table 23. When high-precision tubing is required, it should be specified in the order form; otherwise, standard grade tubing will be supplied. For tubing supplied in multiples of length, each cut should be... It is advisable to leave a 5mm sawing allowance.

5.3.9 Cutting slope The bevel angle of extruded seamed square tubes, flat tubes, hexagonal tubes, and octagonal tubes should conform to the specifications in Table

24.If the buyer requires high precision, this should be specified in the order. If the order form specifies otherwise, the goods will be supplied as standard grade.

5.5.5 Planar clearance The planar clearance of cold-drawn seamed or seamless square and flat tubes should conform to the specifications in Table

34.If the buyer requires high precision, this should be noted in the purchase order. Unless otherwise specified, goods will be supplied as standard grade.

5.5.6 Angle The angular deviation of cold-drawn seamed or seamless square and flat tubes should conform to the specifications in Table

35.If the buyer requires high precision, the requirements should be negotiated between the supplier and the buyer. Please specify this in the order form; otherwise, the product will be supplied as standard grade.

5.5.7 Corner radius (or chamfer radius)

5.5.7.1 For cold-drawn welded or seamless square or flat tubes where the fillet radius (or chamfer radius) is not specified at the sharp corners, rounding of the sharp corners is permitted. Its smoothness and the radius of its fillet (or chamfer) should conform to the specifications in Table

36.The buyer may have special requirements regarding the fillet radius (or chamfer). In such cases, the supply and demand parties shall negotiate and specify the details in the drawings or order form.

5.5.7.2 The deviation of the fillet radius (or chamfer radius) of cold-drawn seamed or seamless square tubes and flat tubes shall conform to the provisions of Table 37.

5.5.8 Length

5.5.8.1 The length of cold-drawn seamed or seamless square tubes and flat tubes supplied in irregular lengths shall not be less than 300mm.

5.5.8.2 The length deviation of cold-drawn welded or seamless square and flat tubes supplied in fixed lengths (or multiple lengths) shall conform to the provisions of Table

38.The buyer requires high precision. When specifying the grade, it should be noted on the order form; otherwise, it will be supplied as ordinary grade. For pipes supplied in multiples of a certain length, a certain amount should be left at each cut. 5mm sawing depth.

5.6.4 Length

5.6.4.1 The length of cold-drawn seamed or seamless elliptical tubes supplied in irregular lengths shall not be less than 300mm.

5.6.4.2 The permissible deviation in length for cold-drawn welded or seamless oval tubes supplied in fixed lengths (or multiple lengths) is 150 mm. Multiple lengths shall be used as the standard length for supply. For pipes, a 5mm sawing allowance should be left for each cut.

5.6.5 Cutting slope The ends of cold-drawn elliptical tubes, whether seamed or seamless, should be cut evenly.

6.2 Dimensional Measurement

6.2.1 Outer diameter, side length, inter-face spacing, major axis and minor axis The outer diameter of the pipe at any point is measured using a measuring instrument with an accuracy of not less than

0.02 mm (see AA or BB in Figure 1). The average diameter of the pipe is... The outer diameter is measured in a vertical position using a measuring instrument with an accuracy of not less than

0.02 mm, and its average value is calculated. The pipe side length is measured using a measuring instrument with an accuracy of not less than

0.02 mm (see AA in Figure 2), and the pipe surface spacing is measured using a measuring instrument with an accuracy of not less than... The measurement was performed using a

0.02 mm measuring tool (see BB in Figure 3). The major and minor axes of the pipe are measured using measuring instruments with an accuracy of not less than

0.02 mm (see AA and BB in Figure 4).

6.2.2 Wall thickness The wall thickness at any point on the circular tube is measured using a measuring instrument with an accuracy of not less than

0.01 mm (see AA or BB in Figure 5). The average wall thickness is measured using an instrument with an accuracy of... A measuring instrument with a diameter of at least

0.01 mm is used to measure at any two locations, and the average value is calculated.

6.2.6 Curvature Place the pipe on the platform and wait for it to stabilize under its own weight. Then, place a 300mm (or 1000mm) long ruler along its length. On the pipe surface, measure the maximum gap (hs) between the pipe and the ruler; this is the curvature of an arbitrary 300mm (or 1000mm) length (see...). Figure 9); Measure the maximum gap (ht) between the pipe and the platform, and divide this value by the total length of the pipe in meters (L) to obtain the "average length per meter". Curvature (see Figure 9).

6.2.7 Planar clearance Place the pipe on the platform and wait for it to stabilize under its own weight. Then, measure the maximum gap between the pipe and the platform in the transverse (width) direction. (f); or place a ruler horizontally on the surface of the pipe and measure the maximum gap (f) between the pipe and the ruler. The maximum gap (f) is the flatness. Surface gap (see Figure 10).

6.2.8 Torque Place the wide side of the pipe on the platform and wait for it to stabilize under its own weight. Then measure the warping caused by twisting along any 1000mm length of the pipe. The maximum height is the twist within an arbitrary 1000mm length; the maximum height (T) that the pipe rises due to twisting along its entire length is the "total length". The degree of twist (see Figure 11).

6.2.9 Angle

6.2.9.1 Square tubes and flat tubes The angles of square and flat tubes are measured using calipers, steel rulers, R gauges, or other measuring tools or specialized instruments of appropriate precision. The deviation (Z) at the (90° angle) is the angle deviation (see Figure 12).

6.2.9.2 Hexagonal tube Use calipers, steel rulers, R gauges, or other measuring tools or specialized instruments of appropriate precision to measure the deviation at the 60° included angle of the hexagonal tube. The value (Z) represents the angular deviation.

6.2.9.3 Octagonal tube Use calipers, steel rulers, R gauges, or other measuring tools or specialized instruments of appropriate precision to measure the deviation at the 45° angle of the octagonal tube. The value (Z) represents the angular deviation.