I. Overview of Cold Rolled Seamless Pipes
(1) Definition and characteristics
Cold rolled seamless pipes is a kind of precision steel tube extruded by rolls at room temperature, and its core features include:
A. High dimensional accuracy: the tolerance of outer diameter can be controlled within ±0.5%, wall thickness tolerance ±10%;
B. Excellent surface quality: low surface roughness (Ra≤0.2μm), no oxide skin or burr;
C. Uniform mechanical properties: cold rolling process can refine the grain, improve tensile strength (such as 45 # steel tensile strength of 600MPa or more).
(2) Production process
The typical process of cold rolled seamless pipe includes:
A. Raw material preparation: select hot rolled seamless pipe or welded pipe as billet;
B. Cold rolling process: wall reduction forming by multi-pass rolling, combined with annealing to eliminate internal stress;
C.Surface treatment: pickling, polishing or galvanising processes to enhance anti-corrosion properties.
(3) Difference with hot rolled seamless pipe
Compared with hot-rolled seamless pipe, cold rolled seamless pipes have thinner wall thickness (as low as 0.25mm), smoother surface, and do not require high temperature treatment, avoiding dimensional deviation caused by thermal deformation.
(4) Application areas
A. Machinery manufacturing: hydraulic cylinders, bearing bushings and other precision parts (such as 40Cr material high wear resistance);
B. Automotive industry: drive shafts, exhaust systems (stainless steel cold rolled tube high temperature resistance, corrosion resistance);
C. Petrochemical industry: high-pressure fluid transport pipelines (carbon steel cold-rolled tube pressure capacity up to 30MPa);
D. Aerospace: lightweight structural components (titanium alloy cold-rolled tube with high strength-to-weight ratio);
E. Building decoration: stainless steel cold-rolled tube for curtain wall support (the surface can be done mirror treatment).
II. Classification and specification of cold rolled seamless pipe:
| Material Type | Representative Grades | Performance Features | Application Scenarios |
|---|---|---|---|
| Carbon Steel | 20#, 45#, Q345 | Low cost (20# approx. $715/ton) Medium strength (45# tensile strength ≥600 MPa) Good welding performance |
Mechanical structural components (bearing housing, gear shaft) Low-pressure fluid conveying pipelines (water, oil) Building support frames |
| Alloy Steel | 40Cr, 16Mn, 42CrMo | High hardness (40Cr HRC 50-55 after quenching) Heat-resistant (16Mn up to 450°C) High impact resistance (42CrMo high toughness) |
Automotive transmission shafts, crankshafts High-pressure hydraulic cylinders (pressure ≥50 MPa) Mining machinery wear-resistant parts |
| Stainless Steel | 304, 316L, 2205 duplex steel | Corrosion-resistant (316L suitable for seawater environment) Bio-compatible (304 medical grade) High-temperature oxidation resistance (up to 800°C) |
Pipelines for food processing equipment Lining for chemical reactors (acid and alkali resistant) Structural components for offshore platforms |
| Tool Steel | T10A, Cr12MoV | Ultra-high hardness (HRC 60-65) Excellent wear resistance (Cr12MoV lifespan increased by 3-5 times) Good red hardness (up to 600°C) |
Mold core (cold extrusion mold) Cutting tools (cutting tools) Precision gauges (gages, plug gauges) |
| High-Temperature Alloy | GH3030, Inconel 625 | Ultra-high temperature resistance (GH3030 up to 1000°C) Anti-creep (Inconel 625 creep strength ≥200 MPa) Strong oxidation resistance |
Aircraft engine nozzles Nuclear power high-temperature heat exchangers Petrochemical cracking furnace tubes |
| Corrosion-Resistant Alloy | Hastelloy C276 | Resistant to strong acids and alkalis (98% sulfuric acid, hydrochloric acid) Anti-intergranular corrosion Anti-stress corrosion cracking (SCC) |
Hydrometallurgical reactors Flue gas desulfurization systems (FGD) Pharmaceutical industry reaction pipelines |
| Titanium and Titanium Alloys | TA2, TC4 | Lightweight (density 4.5 g/cm³) High specific strength (TC4 tensile strength ≥900 MPa) Seawater corrosion resistance |
Submarine pressure hulls Medical implants (bone nails, joints) Seawater desalination plant heat exchanger tubes |
| Aluminum Alloy | 6061, 7075 | Lightweight (density 2.7 g/cm³) Good thermal conductivity (6061 thermal conductivity 167 W/m·K) Anodizing and coloring possible |
Automotive radiator tubes Aerospace hydraulic lines Electronic device heat sink casings |
| Nickel-Based Alloy | Monel 400, Alloy 800 | Resistant to hydrofluoric acid (Monel 400) Anti-carburization (Alloy 800 up to 1100°C) Excellent low-temperature toughness |
Hydrofluoric acid storage and transportation pipelines Ethylene cracking furnace radiant tubes LNG low-temperature pipelines (-196°C) |
Additional Notes:
(1) Material selection priority:
Cost-effective preferred: carbon steel (20#, 45#) for 80% general scenarios;
Corrosion resistance preferred: 316L stainless steel or duplex steel 2205 for chemical/marine environments;
Extreme working conditions: Inconel 625 for high temperature, Hastelloy C276 for strong acid.
(2) Cold rolling process advantages:
Compared with hot rolled seamless pipe, cold rolled pipe wall thickness uniformity increased by 30% (e.g. φ50mm pipe wall thickness difference ≤ 0.05mm);
Compared with cold-drawn seamless pipe, the surface roughness of cold-rolled tubes is reduced by 50% (Ra≤0.2μm), which is more suitable for precision parts.
(3) Customised for special requirements:
Cold rolled tubes for nuclear power need to meet RCC-M standards (grain size ≥ 4, UT flaw grade I pass);
Titanium alloy tubes for medical use need to pass ISO 13485 certification (biocompatibility test + surface passivation treatment).
III. Cold rolled seamless pipe specification parameter table
The following is the specific specification parameter table of cold rolled seamless pipe, split one by one according to the outer diameter, wall thickness, tolerance standard, theoretical weight, data based on national standards (GB/T 3639-2000, GB/T 32957-2016) and industry practice collation:
(1) Small diameter cold rolled seamless pipes (OD 6-60mm)
| Outer Diameter (mm) | Wall Thickness (mm) | Tolerance Standard | Theoretical Weight (kg/m) |
|---|---|---|---|
| 6 | 0.25 | Outer Diameter ±0.5%, Wall Thickness ±10% | 0.035 |
| 6 | 0.4 | Outer Diameter ±0.5%, Wall Thickness ±10% | 0.055 |
| 10 | 0.5 | Outer Diameter ±0.5%, Wall Thickness ±10% | 0.117 |
| 12 | 0.6 | Outer Diameter ±0.5%, Wall Thickness ±10% | 0.169 |
| 25 | 1.2 | Outer Diameter ±0.5%, Wall Thickness ±10% | 0.716 |
| 38 | 2.0 | Outer Diameter ±0.5%, Wall Thickness ±10% | 1.780 |
(2) Medium calibre cold rolled seamless pipes (OD 60-219mm)
| Outer Diameter (mm) | Wall Thickness (mm) | Tolerance Standard | Theoretical Weight (kg/m) |
|---|---|---|---|
| 60 | 3.0 | Outer Diameter ±0.8%, Wall Thickness ±12% | 4.22 |
| 89 | 4.5 | Outer Diameter ±0.8%, Wall Thickness ±12% | 9.38 |
| 108 | 5.0 | Outer Diameter ±0.8%, Wall Thickness ±12% | 12.70 |
| 133 | 6.0 | Outer Diameter ±0.8%, Wall Thickness ±12% | 18.79 |
| 159 | 8.0 | Outer Diameter ±0.8%, Wall Thickness ±12% | 30.28 |
(3) Large-calibre cold-rolled seamless pipes (OD 219-426mm)
| Outer Diameter (mm) | Wall Thickness (mm) | Tolerance Standard | Theoretical Weight (kg/m) |
|---|---|---|---|
| 219 | 6.0 | Outer Diameter ±1.0%, Wall Thickness ±15% | 31.52 |
| 273 | 8.0 | Outer Diameter ±1.0%, Wall Thickness ±15% | 52.28 |
| 325 | 10.0 | Outer Diameter ±1.0%, Wall Thickness ±15% | 78.47 |
| 377 | 12.0 | Outer Diameter ±1.0%, Wall Thickness ±15% | 108.30 |
| 426 | 15.0 | Outer Diameter ±1.0%, Wall Thickness ±15% | 152.90 |
Parameter description and calculation formula
(1) Tolerance standard:
Small-diameter pipe has the highest precision (OD ± 0.5%), and large-diameter pipe is allowed to have a larger deviation (± 1.0%).
Wall thickness tolerance range according to GB/T 32957-2016, cold rolled pipe wall thickness deviation ±10%~15%.
(2) Theoretical weight calculation:
The general formula is [(OD – wall thickness) × wall thickness] × 0.02466 (unit: kg/m).
Example: φ89 × 4.5mm steel pipe weight: (89-4.5) × 4.5 × 0.02466 = 9.38kg/m.
(3) Special specifications:
Ultra-thin wall pipe: outer diameter ≥5mm, wall thickness ≤0.25mm (customised process required).
Shaped pipe: hexagonal, rectangular and other non-standard shapes, which need to be produced by separate moulding.
(4) Cited standards and extended information
GB/T 3639-2000: cold rolled precision seamless steel tube size and surface quality requirements.
GB/T 32957-2016: Tolerance standard for cold rolled tubes for hydraulic/pneumatic systems (ID 25-500mm).
ASTM A519: International Standard for Cold-Rolled Tubes and Pipes for General Mechanical Structures (focusing on mechanical properties).
IV. Cold rolled seamless pipe quality standards and testing methods
(1) Domestic and international quality standards
A. Chinese standard (GB): GB/T 3639-2008 stipulates dimensional accuracy and surface quality;
B. International standards (ASTM/DIN): ASTM A519 focuses on mechanical properties and DIN 2391 emphasises dimensional tolerances;
C. Comparison difference: the national standard allows wall thickness deviation ±10%, while the German standard DIN requires ±8%.
(2) Inspection items and methods
A. Appearance Inspection:
Surface defects: Visual or magnifying glass inspection of scratches, pits (depth ≤ 0.08mm is qualified);
Dimensional accuracy: micrometer to measure the outer diameter, ultrasonic thickness gauge to detect wall thickness uniformity.
B. Internal quality inspection:
Flaw detection technology: ultrasonic flaw detection (UT) to detect internal cracks, magnetic particle flaw detection (MT) for surface defects;
Mechanical properties testing: tensile test (to measure tensile strength, elongation), hardness test (HRC/B scale).
C.Testing equipment and technology
Metallographic analysis: electron microscope to observe the grain size (e.g. 20# steel requires grain size ≥5);
Qualified judgement: with reference to GB/T 2975-2018, the deviation of mechanical properties from the standard value ≤10% is qualified.
Summary:
(1) Cold rolled seamless tubes have become the core material in the field of precision manufacturing by virtue of their high precision, high strength and diverse surface treatment processes.
(2) Procurement needs to be combined with application scenarios to choose the material and standards (such as chemical recommended 316L stainless steel + pickling process), and strict control of the testing process (such as UT flaw detection + mechanical properties test).
(3) For special needs, it is recommended to communicate with the manufacturer in depth customised solutions to ensure that the technical parameters and costs can be controlled.
