Submerged Arc Welded Square Tube

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Published Date：2026-02-03 16:14:20

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I. Technical Standards

Explanation of indexing symbols:

B-Side length;

t -Wall thickness;

R-0uter arc radius;

r - lnner arc radius

Submerged Arc Welded Square Tube

Explanation of indexing symbols:

H - Length of the long side;

B -Length of the short side;

t-Wall thickness;

R-0uter arc radius;

r- Inner arc radius;

(1) Specifications

Square Tube Specification Table
		Material and Thickness (mm)
Serial numbe	Side length mm	Q235	Q355	Q420	Q460	Q690	Length
1	300	14~25	14~25	14~25	14~25	14~25	6m~12m
2	350	14~25	14~25	14~25	14~25	14~25	6m~12m
3	400	14~30	14~30	14~30	14~30	14~25	6m~12m
4	450	14~30	14~30	14~30	14~30	14~30	6m~12m
5	500	14~40	14~40	14~30	14~30	14~30	6m~12m
6	600	14~45	14~40	14~40	14~40	14~35	6m~12m
7	700	14~50	14~45	14~42	14~42	14~38	6m~12m
8	800	14~50	14~50	14~48	14~45	14~40	6m~12m
9	900	14~50	14~50	14~50	14~50	14~42	6m~12m
10	1000	14~50	14~50	14~50	14~50	14~42	6m~12m

Rectangular Tube Specification Table
		Material and Thickness (mm)
Serial numbe	Width mm	Length mm	Q235	Q355	Q420	Q460	Q690	Length
1	200	400	14~20	14~20	14~20	14~20	14~18	6m~12m
2	200	500	14~20	14~20	14~20	14~20	14~18	6m~12m
3	250	400	14~20	14~20	14~20	14~20	14~20	6m~12m
4	250	500	14~20	14~20	14~20	14~20	14~20	6m~12m
5	200	600	14~20	14~20	14~20	14~20	14~18	6m~12m
6	300	500	14~30	14~30	14~25	14~25	14~25	6m~12m
7	400	500	14~30	14~30	14~30	14~30	14~25	6m~12m
8	400	600	14~30	14~30	14~30	14~30	14~25	6m~12m
9	300	1200	14~30	14~30	14~25	14~25	14~25	6m~12m
10	500	1000	14~10	14~40	14~30	14~30	14~30	6m~12m

(2) Length and allowable deviation

1. Closed-end steel sections are typically delivered in lengths ranging from 4000 mm to 12000 mm. Other length options may be supplied upon mutual agreement between the supplier and the client.

2. For closed-end steel sections delivered in fixed-length or multiple-length units, this shall be specified in the contract. The allowable length deviation shall comply with the provisions in the table. If the contract does not specify the fixed-length precision, standard fixed-length delivery shall be adopted.

The unit is millimeters
Fixed length precision	Length	Allowable deviation
Regular fixed length	4 000~12 000	+500
Precise sizing	4 000~6 000	+500
Precise sizing	>6 000~12 000	+100

3. Closed-end steel sections are not permitted for butt joint delivery. Short sections and non-standard sections with a minimum length of 2000mm are allowed for delivery. The weight of short sections and non-standard sections shall not exceed 5% of the total delivery quantity. For steel sections with theoretical weight exceeding 20kg/m², the proportion shall not exceed 10% of the total delivery quantity.

(3) Appearance

1. Determination of bending deviation: The bending degree of the section steel should not be greater than 2mm per meter, and the total bending degree should not be greater than 0.15% of the total length. The measurement method is shown in the figure.

Submerged Arc Welded Square Tube

Explanation of indexing symbols:

L一Length;

e- Curvature.

2. Measurement of the torsion degree of square or rectangular section steel: Upon negotiation between the supplier and the buyer and as specified in the contract, the torsion degree of closed cold-formed steel sections can be measured, and the measurement shall be carried out on a platform. The measurement method is as shown in the figure, and the measured value shall be less than the specified value and calculated according to the formula: V = 2 + L × 0.5 / 1000

In the formula:

V-Torsion degree, in millimeters (mm);

L -Length, in millimeters (mm).

Submerged Arc Welded Square Tube

Explanation ofindexing symbols:

V一Degree of torsion.

3. The ends of the section steel shall be cut straight and square, and the sawing slope shall comply with the provisions in Table 23. Minor deformations and burrs caused by the cutting method are allowed.

The unit is millimeters
Maximum nominal side length (or nominal outer diameter)	Sawing slope, less than
≤100	2
>100~300	4
>300~500	6
>500	Agreement

4. For open and closed cold-formed steel products that use online thermal cutting processes such as laser cutting or plasma arc cutting, the presence of tiny cutting cracks, nodules, and cutting puncture notches is allowed. When the total side length of open and closed steel sections exceeds 700mm, more than two cutting puncture notches are allowed on the same cutting cross-section.

Note 1: Cutting lines refer to the lines left on the cutting surface of the workpiece being cut after the cutting jet blows away the material during the cutting process.

Note 2: Nodulation refers to the phenomenon where, during fusion cutting (such as plasma arc cutting and laser cutting), while the molten metal is blown off at high speed, a portion of it adheres to the lower edge of the cutting surface and solidifies, and this attachment is called nodulation.

(4) Weight and Allowable Deviation

Section steel shall be delivered by actual weight. At the request of the buyer, upon negotiation between the buyer and the seller and specified in the contract, it can also be delivered by theoretical weight.

When delivering by theoretical weight, if the total side length of the section steel does not exceed 1600mm, the allowable deviation between the actual weight and the theoretical weight of each batch of section steel shall be -6% to +10%. When the total side length of the section steel exceeds 1600mm, the allowable deviation between the actual weight and the theoretical weight of each batch of section steel shall be -4% to +6%.

(5) Mechanical Properties

1. The yield strength, tensile strength, and elongation after fracture of section steel shall comply with the provisions in Table 25. The mechanical properties of Q195, Q215, stainless steel or other steel grades shall be determined through negotiation between the supplier and the buyer.

Serial numbe	Product yield strength grade	Upper yield strength ReH/MPa Not less tha	Tensile strength Rm/MPa	Elongation after fracture A/% Not less than
1	235	235	370~560	24
2	355	355	470~680	20
3	390	390	490~700	18
4	420	420	520~730	Agreement
5	460	460	550~770	Agreement
6	500	500	610~820	Agreement
7	550	550	670~880	Agreement
8	620	620	710~940	Agreement
9	690	690	770~1000	Agreement
10	750	750	750~1010	Agreement
For cold-formed steel products with a cross-sectional dimension not greater than 60mm x60mm (including circular and rect-angular cold-formed steels with equal perimeter dimensions) or cold-formed steel products with an edge (shortedge) thick-ness ratio not greater than 14, the percentage elongation after fracture of the flat part is allowed to be 3% (absolute value) lower than the specified value in the table, and the width of the tensile sample used is 12.5mm.

2. Through negotiation between the supplier and the buyer, and as specified in the contract, impact tests can be conducted on cold-formed steel with a thickness of not less than 6mm. The results of the impact tests and their re-tests shall comply with the provisions of relevant raw material standards such as GB/T699, GB/T700, GB/T714, GB/T1591, and GB/T4171.

(6) Weld quality

1. External weld quality

The closed-section steel welds shall not have weld breaks, overlapping welds, burn-through, misalignment, or arc craters. Defects in the welds are allowed to be repaired by welding and grinding, but after repair, they shall be smooth and flat, and the thickness after grinding shall not be less than the minimum allowable thickness.

2. External burrs of welds

The external burrs at the welds of closed-section steel shall be removed, and the remaining height of the weld after removal shall generally not exceed 0.5mm. The internal burrs at the welds are generally not removed; if there are special requirements, they shall be determined through negotiation between the supplier and the buyer.

3. Internal weld quality

The internal welds of closed-section steel shall be continuous, uniform and full.

4. Other requirements

Through negotiation between the supplier and the buyer and as specified in the contract, additional requirements for the weld position, inspection of the mechanical properties and technological properties of the welds, as well as non-destructive testing can be added.

II. Disclaimer

1. Unless otherwise guaranteed, the technical information, specifications, etc. contained in this document are all reference values and do not constitute an official guarantee.

2. Customers shall independently confirm the applicability and performance of this product based on the purpose of use, conditions of use, etc.

3. Our company shall not be liable for any damages arising from the use of this product, etc.

Note: Executable standards: GB/T6728-2025, European standard: EN10219, Russian standard: GOST series