| Customization: | Available |
|---|---|
| Type: | Round |
| Standard: | AISI, ASTM, DIN, JIS, GB, BS |
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GB/T 3091-2015 Standard Welded Steel Pipes for Low Pressure Liquid Conveyance
| Attribute | GB/T 3091 (latest: 2025) |
|---|---|
| Standard & Scope | GB/T 3091-2025 - Welded steel pipes for low-pressure fluid conveyance |
| Pipe Type | ERW, LSAW, SSAW (spiral) |
| Outside Diameter | 10.2 - 1 820 mm |
| Wall Thickness | 0.8 - 50 mm |
| Length | 3 - 12 m (fixed or random) |
| Delivery Condition | As-welded + optional galvanizing |
| Typical Grades | Q195, Q215A/B, Q235A/B, Q345A/B |
| Chemical (example Q235B) | Same as GB/T 700 |
| Mechanical (Q235B) | Same as GB/T 700 |
| Welding Type | ERW, LSAW, SSAW |
| Surface Finish | Mill, black, galvanized |
| Testing | Hydrostatic 1.5×PN, flattening, bend, dimensional |
| Certification | EN 10204 3.1/3.2, CE mark |
| Applications | Municipal water, steam, air, gas, HVAC |
| Packing | Packed by Bundles, Plastic Bgas, Wooden case |
The GB/T 3091-2015 standard, titled "Welded steel pipes for low-pressure fluid conveyance," establishes the technical delivery conditions and quality benchmarks for welded steel pipes used in a vast array of general-purpose applications. As a pivotal update to its predecessors, this Chinese National Standard delineates the requirements for pipes that form the backbone of municipal water systems, gas lines, and structural frameworks globally. For engineers, project managers, and procurement specialists, understanding this specification is key to sourcing reliable, cost-effective, and safe piping solutions for non-critical pressure systems.
This product represents a category of electric resistance welded (ERW) steel pipes, celebrated for their balanced performance, economic viability, and manufacturing efficiency. Compliance with GB/T 3091-2015 is not merely a claim of manufacture; it is a verifiable promise of dimensional integrity, mechanical strength, and functional performance, backed by a rigorous regimen of factory tests.
Core Manufacturing and Material Composition
The production of these pipes begins with coiled steel strips, which are cold-formed through a series of rolls into a cylindrical shape. The critical seam is created using the Electric Resistance Welding (ERW) process, where high-frequency electrical current fuses the edges together without the use of filler metal, resulting in a strong, homogeneous weld line.
The steel grades stipulated under this standard, such as Q195, Q215, Q235, and Q275, are carbon steels where the alphanumeric code indicates the yield strength. For instance, Q235 guarantees a minimum yield point of 235 MPa. These grades are predominantly supplied as rimmed steel, which offers excellent surface quality and formability, ideal for the welding and subsequent galvanizing processes. The chemical composition of these steels is carefully controlled to ensure consistent weldability and the necessary mechanical properties, while avoiding alloying elements that would unnecessarily increase cost for these applications.
Dimensional Scope and Tolerances: A Fit for Every Purpose
The standard covers an extensive range of sizes to meet diverse project needs. The nominal diameter (DN) spectrum spans from a small 6 millimeters (approximately ¼ inch) up to a substantial 600 millimeters (24 inches). Corresponding wall thicknesses are meticulously graded, typically from 0.8mm for smaller diameters to 10.0mm for larger ones, ensuring each pipe can handle its designated pressure rating.
Adherence to precise dimensional tolerances is a hallmark of GB/T 3091-2015 compliance. Permissible deviations for outer diameter and wall thickness are explicitly defined. For example, a pipe with a DN of 40mm must have an outer diameter within ±0.50mm of the nominal value, while wall thickness is generally held to a tolerance of ±10%. This precision guarantees ease of installation, compatibility with standard fittings, and predictable performance in the field. Standard lengths are typically 6 meters or 12 meters, with custom lengths available to suit specific project layouts.
Surface Treatment: Galvanized vs. Black Variants
A defining feature of this standard is the specification for two distinct surface conditions, each serving a different operational environment:
Hot-Dip Galvanized (Z): This is the most common and protective finish. After fabrication and testing, the pipes are immersed in a bath of molten zinc. This process creates a metallurgically bonded coating that provides robust, long-lasting defense against corrosion. The standard mandates a minimum zinc coating mass (e.g., ≥500 g/m² for pipes over DN 125mm), ensuring a thick, durable layer suitable for underground burial, outdoor exposure, and humid environments. The characteristic spangled appearance is a visual indicator of this high-quality finish.
Black (U): These pipes are supplied in their as-welded state, with a mill scale surface and often coated with a temporary rust-preventative oil. They are intended for indoor applications, concealed conduits, or situations where the pipe will be professionally painted or otherwise coated on-site. They offer a lower initial cost and are perfectly suited for dry, non-corrosive settings or temporary structural supports.
Verification Through Rigorous Testing
The integrity of every batch of GB/T 3091-2015 pipes is validated through a series of mandatory destructive and non-destructive tests:
Hydrostatic Test: Every single pipe is subjected to an internal water pressure test. The test pressure is calculated based on the steel grade, wall thickness, and diameter, ensuring the pipe can safely withstand more than its intended operational pressure without leakage or deformation.
Flattening Test: A sample section of the pipe is flattened between two parallel plates to a specified height. This severe deformation tests the ductility of the base metal and the quality of the weld, which must remain intact without cracking.
Bend Test: For smaller diameter pipes (typically DN ≤ 50mm), a cold bend test is performed. A sample is bent around a mandrel to a 90-degree angle, verifying its formability and the absence of brittle fractures.
Tensile Test: Carried out on coupons taken from the pipe body, this test confirms that the steel's yield strength, tensile strength, and elongation at break meet the minimum requirements for its designated grade.
Reverse Bend Test (for Galvanized Pipes): A specific test for the zinc coating, where a sample strip is bent 180 degrees to check for any flaking or peeling, confirming the coating's adhesion.
Diverse Applications Across Industries
The versatility of GB/T 3091-2015 pipes makes them indispensable in multiple sectors:
Municipal Infrastructure: As the primary conduit for potable water distribution and low-pressure natural gas supply to residential and commercial buildings.
Construction and Architecture: Widely used in scaffolding, structural frames, handrails, fence posts, and as protective conduits for electrical wiring.
HVAC Systems: Serving as ductwork and pipes for conveying air and low-pressure heating/cooling fluids.
Agricultural Irrigation: Transporting water across farms and fields.
Industrial Utility Lines: Providing compressed air, process water, and other non-hazardous fluids within factory settings.
Conclusion: The Smart Choice for Standardized Quality
In summary, GB/T 3091-2015 Standard Welded Steel Pipes represent a mature, well-defined, and highly reliable product category. They offer an optimal balance of strength, durability, and cost-effectiveness for a multitude of low-pressure and structural applications. By specifying this standard, buyers and engineers are not just purchasing a pipe; they are investing in a product backed by a comprehensive system of material, dimensional, and performance guarantees, ensuring project success, safety, and longevity. For any application where standardized quality and proven performance are paramount, this standard provides an unequivocal specification to guide procurement and installation.
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