St3sp · 09G2S · 20×10–300×200 · GOST 8645 · GOST 30245
Rectangular hollow section
Closed rectangular section for purlins, beams and frames. Wall 1–12 mm, St3sp, 09G2S, Q235B, Q355B
St3sp · 09G2S · 15×15–300×300 · GOST 8639 · GOST 30245
Square hollow section
Closed square section for frames, trusses and fencing. Wall 1–12 mm, St3sp, 09G2S, Q235B, Q355B
GOST 8639-82GOST 13663-86GOST 30245-2003GB/T 6728-2017ASTM A500/A500MEN 10219-1St2spSt3spSt3ps09G2SQ235BQ355BS235JRHS355J2HA500 Gr.B
Parameters
| Parameters | |
|---|---|
| Side of section | 15×15 – 300×300 mm |
| Wall thickness | 1.0–12 mm |
| Length | 6 and 12 m; fixed length to specification |
| Steel grade | St3sp, 09G2S; Q235B, Q355B per GB |
| Acceptance standard | GOST 8639 and GOST 13663; GOST 30245 for building structures |
| Weld | single, on the corner; outer weld bead removed |
Sizes and weight
| Size, mm | Weight, kg/m |
|---|---|
| 15×15×1.5 | 0.605 |
| 20×20×1.5 | 0.841 |
| 25×25×2 | 1.39 |
| 30×30×2 | 1.7 |
| 40×40×2 | 2.33 |
| 40×40×3 | 3.36 |
| 50×50×3 | 4.31 |
| 60×60×3 | 5.25 |
| 80×80×4 | 9.33 |
| 100×100×5 | 14.6 |
| 120×120×5 | 17.7 |
| 150×150×6 | 26.6 |
| 200×200×8 | 47.4 |
| 300×300×10 | 89.7 |
Theoretical weight at steel density 7.85 g/cm³. Actual batch weight is by scale and mill certificate.
Description
A square hollow section is a closed welded profile with four flat faces and rounded corners. Mills make it in two ways: a round welded pipe is shaped into a square on sizing rolls, or the strip is formed directly into a square section and welded on one face. Size range to GOST 8639-82, technical requirements to GOST 13663-86, for building structures — GOST 30245-2003 with specified mechanical properties. At mills in China this is GB/T 6728-2017, for export ASTM A500/A500M and EN 10219-1 for cold-formed sections.
The grades are the same as for welded pipe: St2sp, St3sp and St3ps for fencing and light frames, 09G2S for load-bearing structures and service at sub-zero temperatures. At mills in China St3sp corresponds to Q235B, 09G2S to Q355B; in export versions S235JRH and S355J2H under EN 10219, A500 Gr.B and Gr.C under ASTM. For structural design not only the yield strength matters but also the outside corner radius: it limits the section modulus and is set by the standard depending on wall thickness; the specification records the standard to which the section is accepted.
During inspection at the mill, both sides of the square section are measured with callipers at the ends of the sampled lengths, the wall thickness with a micrometer on a flat face away from the weld. Concavity and convexity of the faces are checked with a rule and feeler gauge, twist along the length, corner radius with a template, condition of the weld and ends. The heat number in the marking is matched against the mill test certificate (MTC): chemical composition and mechanical properties for sections to GOST 30245. The bundle tag and strapping are checked. Rejects recorded in the report are replaced; the replacement is supplied by the manufacturing mill under its contract with the bureau.
Applications
- columns and posts of light frames and hangars
- trusses, purlins and bracing
- fencing, gates, railings
- frames for greenhouses, canopies and retail pavilions
- equipment frames and bases
- advertising and lighting poles
Packing and shipment
Rectangular bundles strapped with steel band; the bundle carries a mill tag with size, wall thickness, grade and heat number.
Grade equivalents
| GOST | GB (China) | ASTM | EN | Note |
|---|---|---|---|---|
| Steel 20 | 20# | A106 Gr.B | P235GH | Seamless pipes. Nearest equivalents by composition and strength; test requirements differ between the standards |
| Steel 45 | 45# | 1045 (A519) | C45 | Seamless pipes for machining, nearest equivalents. A519 is a standard for mechanical tubing; C45 under EN 10083 is a steel grade, tubes in it are made to EN 10297-1 |
| 09G2S | Q355B | A572 Gr.50 | S355J2H | Low-alloy steel, nearest equivalents. Before GB/T 1591-2018 the grade was designated Q345B; A572 is a standard for rolled products, not for pipe; S355J2H is a hollow section grade under EN 10219 |
| St3sp | Q235B | A53 Gr.B | P235TR1 | Welded pipes. A53 Gr.B is the nearest equivalent: its tensile strength is higher than that of Q235B |
| St3sp | Q235B | A500 Gr.B | S235JRH | Hollow sections. A500 specifies a higher yield strength than Q235B; structural design uses the standard stated in the specification |
| St2sp, St3sp | Q195, Q235 | A53 Gr.A | S195T | Water and gas pipes. GOST 3262 does not specify mechanical properties, so the grade comparison is nominal |
| K42 (GOST 20295) | L245 (GB/T 9711) | API 5L Gr.B | L245NB | Spiral-welded pipes. A strength class by tensile strength, not a steel grade |
| 08Kh18N10 | 06Cr19Ni10 | TP304 | 1.4301 | Stainless pipes. Austenitic 18-10 steel; 03Kh17N14M3 corresponds to TP316L and 1.4404 |
Equivalents are the closest match, not identical: chemistry and tolerances differ between standards. The exact grade and standard are written into the contract.
Related items
St3sp · Q235B · Ø57–530 · GOST 10704
Longitudinally welded pipe
Round pipe from strip with a high-frequency weld. Structures, fencing, low-pressure water and gas
Buyer questions
How to read a mill test certificate for pipe
The certificate (MTC) states the standard, steel grade, size, heat number, chemical composition by element, mechanical properties of the test specimens (yield strength, tensile strength, elongation), the hydrostatic test result and, for welded pipe, the result of non-destructive testing of the weld. The heat number in the certificate is matched against the marking on the pipe and the bundle tag: this is the only link between the document and the metal. The bureau checks this match at the mill before shipment and attaches the certificate to the inspection report.
How a seamless pipe differs from a welded one and when each is needed
A seamless pipe is rolled from a solid billet, it has no weld, and it goes where there is pressure, temperature or alternating load: boiler plants, steam, hydraulics, machine parts. A welded pipe is formed from strip and welded by high-frequency current; at the same size it is simpler to produce, and the weld passes a hydrostatic test and non-destructive testing. For structures, fencing, water lines and low-pressure gas lines a welded pipe does the job. The choice is fixed in the specification by the project, not by price.
How the tonnage of a pipe batch is calculated
The theoretical weight per metre of round pipe is calculated as 0.02466 · (D − t) · t, where D is the outside diameter and t the wall thickness in millimetres, steel density 7.85 g/cm³. For a hollow section: 0.0157 · t · (a + b − 2.86 · t). The actual weight is determined by weighing at the mill and is stated in the packing list. Whether settlement is by theoretical or actual weight is fixed in the specification before the order is placed: on thin walls the difference between them is noticeable.
What is checked during batch inspection of pipes at the mill
Outside diameter and wall thickness with a micrometer and callipers at both ends of the sampled pipes, ovality, wall-thickness variation, straightness, condition of the ends and bevel, the weld of welded pipe from outside and, where accessible, from inside, marking on every pipe, the bundle tag and matching of the heat number against the mill test certificate. The results are entered in a report with photo documentation. Rejects recorded in the report are replaced; the replacement is supplied by the manufacturing mill under its contract with the bureau.
What quantity can be ordered
The batch is sized to your quantity — send a specification with sizes, grades, acceptance standard and lengths. The manufacturing mill confirms the batch for a specific size range; the bureau agrees the inspection and acceptance procedure in the contract. Several sizes in one batch are sourced from one mill or from several if their size ranges differ.
Price request
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Steel pricing depends on grade, size, tonnage and delivery terms on the day of contract. A number on the page would be wrong by the time you read it.
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