I. Overview of Cold Rolled Seamless Pipes
(1) Definition and Characteristics
Cold rolled seamless tubes are a kind of precision steel tubes extruded by rolls at room temperature, whose core characteristics include:
A. High dimensional accuracy: the tolerance of the outer diameter can be controlled within ±0.5%, and the tolerance of the wall thickness is ±10%;
B. Excellent surface quality: the surface roughness is low (Ra ≤ 0.2μm), no oxidized skin or burrs;
C. Uniform mechanical properties: cold rolling process can refine the grain, improve the tensile strength (such as 45 # steel tensile strength of 600MPa or more).
(2) Production process
Typical processes of cold rolled seamless pipe include:
A. Raw material preparation: select hot rolled seamless pipe or welded pipe as billet;
B. Cold rolling process: reduce wall molding through multiple rolling passes, combined with annealing to eliminate internal stresses;
C. Surface treatment: Pickling, polishing or galvanizing and other processes to enhance anti-corrosion properties.
(3) Difference with Hot Rolled Seamless Pipes
Compared with hot rolled seamless tubes, cold rolled seamless tubes have thinner wall thickness (can be 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: High-pressure fluid transportation pipeline (carbon steel cold-rolled tube pressure capacity up to 30MPa);
D. Aerospace: lightweight structural components (titanium alloy cold-rolled tube strength to weight ratio is high);
E. Architectural decoration: stainless steel cold-rolled tube used for curtain wall support (the surface can be made of 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# ~5000 CNY/ton) Medium strength (45# tensile strength ≥600 MPa) Good weldability |
Mechanical structural components (bearing housings, gear shafts) Low-pressure fluid conveying pipelines (water, oil) Building support frames |
| Alloy Steel | 40Cr, 16Mn, 42CrMo | High hardness (40Cr quenched HRC 50-55) High-temperature resistance (16Mn up to 450°C) High impact resistance (42CrMo high toughness) |
Automotive drive shafts, crankshafts High-pressure hydraulic cylinders (pressure ≥50 MPa) Mining machinery wear-resistant components |
| Stainless Steel | 304, 316L, 2205 duplex steel | Corrosion-resistant (316L resistant to Cl⁻, suitable for seawater environments) Biocompatibility (304 medical grade) High-temperature oxidation resistance (up to 800°C) |
Food processing equipment pipelines Chemical reactor linings (acid and alkali resistance) Marine platform structural components |
| Tool Steel | T10A, Cr12MoV | Ultra-high hardness (HRC 60-65) Excellent wear resistance (Cr12MoV 3-5 times longer life) Good red hardness (up to 600°C) |
Mold core bars (cold extrusion molds) Cutting tools (machining tools) Precision gauges (gages, plug gauges) |
| High-Temperature Alloy | GH3030, Inconel 625 | Ultra-high-temperature resistance (GH3030 up to 1000°C) High creep resistance (Inconel 625 ≥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 Resistant to 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 screws, 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) Anodizable and colorable |
Automotive radiator tubes Aerospace hydraulic lines Electronic device heat sink housings |
| 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 section tubes LNG low-temperature pipelines (-196°C) |
Supplementary note:
(1) material selection priority:
Cost-effective first choice: carbon steel (20 #, 45 #) for 80% of the general scenarios;
corrosion resistance priority: 316L stainless steel or duplex steel 2205 for chemical / marine environment;
extreme Extreme conditions: Inconel 625 for high temperature, Hastelloy C276 for strong acid.
(2) Cold Rolling Process Advantages:
Compared with the hot rolled seamless pipe, the uniformity of wall thickness of cold rolled pipe is increased by 30% (e.g., the difference in wall thickness of φ50mm pipe is ≤0.05mm);
Compared with the cold drawn seamless pipe, the surface roughness of the cold rolled pipe is reduced by 50% (Ra ≤0.2μm), which is more suitable for precision components. More suitable for precision parts.
(3) Customized for special requirements:
Cold rolled tubes for nuclear power need to meet the RCC-M standard (grain size ≥ 4, UT flaw grade I pass).
III. Cold Rolled Seamless Pipes Specification Parameter Table
The following is a specific specification parameter table for cold rolled seamless tubes, split one by one according to the outer diameter, wall thickness, tolerance standards, theoretical weight, the data is based on national standards (GB/T 3639-2000, GB/T 32957-2016) and industry practice to organize:
Small diameter cold rolled seamless tubes (OD 6-60mm)
| Outer Diameter (mm) | Wall Thickness (mm) | Tolerance Standard | Theoretical Weight (kg/m) |
|---|---|---|---|
| 6 | 0.25 | ±0.5% OD, ±10% WT | 0.035 |
| 6 | 0.4 | ±0.5% OD, ±10% WT | 0.055 |
| 10 | 0.5 | ±0.5% OD, ±10% WT | 0.117 |
| 12 | 0.6 | ±0.5% OD, ±10% WT | 0.169 |
| 25 | 1.2 | ±0.5% OD, ±10% WT | 0.716 |
| 38 | 2.0 | ±0.5% OD, ±10% WT | 1.780 |
Medium caliber cold rolled seamless pipe (OD 60-219mm)
| Outer Diameter (mm) | Wall Thickness (mm) | Tolerance Standard | Theoretical Weight (kg/m) |
|---|---|---|---|
| 60 | 3.0 | ±0.8% OD, ±12% WT | 4.22 |
| 89 | 4.5 | ±0.8% OD, ±12% WT | 9.38 |
| 108 | 5.0 | ±0.8% OD, ±12% WT | 12.70 |
| 133 | 6.0 | ±0.8% OD, ±12% WT | 18.79 |
| 159 | 8.0 | ±0.8% OD, ±12% WT | 30.28 |
Large-caliber cold-rolled seamless pipes (OD 219-426mm)
| Outer Diameter (mm) | Wall Thickness (mm) | Tolerance Standard | Theoretical Weight (kg/m) |
|---|---|---|---|
| 219 | 6.0 | ±1.0% OD, ±15% WT | 31.52 |
| 273 | 8.0 | ±1.0% OD, ±15% WT | 52.28 |
| 325 | 10.0 | ±1.0% OD, ±15% WT | 78.47 |
| 377 | 12.0 | ±1.0% OD, ±15% WT | 108.30 |
| 426 | 15.0 | ±1.0% OD, ±15% WT | 152.90 |
Parameter Description and Calculation Formula
(1) Tolerance standards:
Small-diameter pipe has the highest precision (OD ± 0.5%), and large-diameter pipe is allowed to deviate more (± 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-walled pipe: OD ≥ 5mm, wall thickness ≤ 0.25mm (need to be customized process).
Shaped pipe: hexagonal, rectangular and other non-standard shapes, need to be separately molded production.
(4) Cited standards and extended information
GB/T 3639-2000: Dimensions and surface quality requirements for cold rolled precision seamless steel tubes.
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. Quality Standards and Testing Methods for Cold Rolled Seamless Pipes
(1) Domestic and International Quality Standards
A. Chinese Standard (GB): GB/T 3639-2008 stipulates dimensional accuracy and surface quality;
B. International Standard (ASTM/DIN): ASTM A519 focuses on mechanical properties, while DIN 2391 emphasizes dimensional tolerances;
C. Comparison Differences: 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 the uniformity of wall thickness.
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 test: tensile test (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 judgment: refer to GB/T 2975-2018, mechanical properties and standard value deviation ≤10% is qualified.
Summarize:
(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 to customize the program to ensure that the technical parameters and costs can be controlled.
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