High Precision Automotive Steel Pipe Seamless Steel Pipe For Car ISO9001
Product Overview
High precision automotive steel pipe is a cold-drawn seamless mechanical tube designed for components requiring accurate inside and outside diameters, controlled wall thickness, low surface roughness, and stable mechanical properties. It is primarily used for manufacturing automotive shock absorber cylinder barrels where dimensional consistency directly affects piston movement, sealing performance, oil retention, and service life.
The tubes can be supplied in cold-drawn, stress-relieved, annealed, or normalized conditions. Precision cutting, internal honing, external polishing, phosphating, and customized tolerance control are available according to the final machining and assembly requirements.
ISO 9001 refers to the manufacturer's quality management system rather than a steel tube material standard. Product conformity should therefore be specified separately according to EN 10305-1, ASTM A519, JIS G 3445, GB/T 3639, or another agreed technical standard.
Technical Specifications
| Item |
Specification |
| Product |
High Precision Seamless Automotive Steel Pipe |
| Manufacturing Method |
Seamless cold drawing |
| Material |
Carbon steel or low-alloy mechanical steel |
| Main Standards |
EN 10305-1, ASTM A519/A519M, JIS G 3445, GB/T 3639, DIN 2391 |
| Typical Grades |
E235, E355, SAE 1020, SAE 1026, STKM11A, STKM12C, STKM13C, 20, 45 |
| Outside Diameter |
6-200 mm |
| Wall Thickness |
0.5-20 mm |
| Length |
1-12 m, customizable |
| Standard OD Tolerance |
According to the selected product standard |
| Precision OD Tolerance |
Up to ±0.05 mm for suitable size ranges |
| Precision ID Tolerance |
H8 or customized dimensional tolerance |
| Wall Thickness Tolerance |
Normally ±10%; precision control up to ±5% by agreement |
| Straightness |
≤0.5 mm/m; ≤0.3 mm/m available for selected dimensions |
| Internal Surface Roughness |
As-drawn Ra ≤3.2 μm; honed Ra ≤0.4 μm |
| Surface Condition |
Cold drawn, bright, phosphated, oiled, polished, honed, or customized |
| Heat Treatment |
+C, +LC, +SR, +A, or +N |
| Inspection |
Dimensional inspection, tensile test, hardness test, flattening test, flaring test, eddy-current test, or ultrasonic test |
| Quality Management |
ISO 9001 quality management system |
| Documentation |
EN 10204 3.1 inspection certificate available |
Key Characteristics
- Controlled Inside Diameter: Cold drawing through a die and over a mandrel provides closer control of the inside diameter than conventional hot-finished seamless tubing.
- Low Internal Surface Roughness: Honed bore with Ra ≤0.4 μm reduces friction between the piston seal and cylinder wall, supporting stable hydraulic oil distribution.
- Tight Wall Thickness Consistency: Precision cold drawing improves wall thickness uniformity and reduces eccentricity to ≤10% of nominal wall thickness.
- High Straightness: Standard straightness controlled to ≤0.5 mm per metre, with selected dimensions available to ≤0.3 mm per metre.
- Stable Mechanical Properties: Delivery condition can be selected according to subsequent manufacturing process requirements.
- Clean Seamless Structure: Seamless production route eliminates longitudinal weld seam, providing uniform circumferential structure.
Production Process
Billet Inspection → Heating and Piercing → Hot Rolling or Elongation → Pickling → Lubrication → Cold Drawing → Intermediate Heat Treatment → Final Cold Drawing → Straightening → Cutting → Honing or Polishing → Non-Destructive Testing → Dimensional Inspection → Surface Protection → Packing
Quality Advantages
- Bore Tolerance and Surface Roughness Control: We control the tube according to final component requirements rather than checking only nominal outside diameter.
- Matched Delivery Conditions: Delivery condition can be selected according to the next manufacturing operation for optimal performance.
- Component-Based Inspection: Inspection requirements can be converted directly from customer's component drawing into a tube control plan.
Execution Standards
| Standard System |
Applicable Standard |
Brief Description |
| ASTM |
ASTM A519/A519M |
Seamless carbon and alloy steel mechanical tubing in hot-finished or cold-finished conditions |
| EN |
EN 10305-1 |
Seamless cold-drawn steel tubes for precision applications |
| JIS |
JIS G 3445 |
Carbon steel tubes for machine structures, including automotive components |
| GB |
GB/T 3639 |
Cold-drawn or cold-rolled precision seamless steel tubes |
| DIN |
DIN 2391 |
Traditional German specification for precision seamless steel tubes |
Primary Application
Automotive Shock Absorber Cylinder Barrel: The tube is used as the hydraulic cylinder barrel of an automotive shock absorber. After precision cutting and internal honing, the bore guides the piston and sealing system while containing hydraulic oil under repeated compression and rebound cycles.
Chemical Composition
| Grade |
C |
Si |
Mn |
P |
S |
| STKM11A |
≤0.12 |
≤0.35 |
≤0.60 |
≤0.040 |
≤0.040 |
| STKM12A |
≤0.20 |
≤0.35 |
≤0.60 |
≤0.040 |
≤0.040 |
| STKM12C |
≤0.20 |
≤0.35 |
≤0.60 |
≤0.040 |
≤0.040 |
| STKM13A |
≤0.25 |
≤0.35 |
0.30-0.90 |
≤0.040 |
≤0.040 |
| STKM13C |
≤0.25 |
≤0.35 |
0.30-0.90 |
≤0.040 |
≤0.040 |
Mechanical Properties
| Grade |
Tensile Strength Rm, MPa Min. |
Yield Strength or Proof Stress, MPa Min. |
Elongation, % Min. |
| STKM11A |
290 |
Not specified |
35 |
| STKM12A |
340 |
175 |
35 |
| STKM12C |
470 |
355 |
20 |
| STKM13A |
370 |
215 |
30 |
| STKM13C |
510 |
380 |
15 |
Surface and Heat-Treatment Options
| Code |
Delivery Condition |
Processing Description |
Recommended Use |
| +C |
Cold Drawn / Hard |
No heat treatment after final cold drawing |
High strength and subsequent machining |
| +LC |
Cold Drawn / Soft |
Light final cold drawing after heat treatment |
Moderate forming and machining |
| +SR |
Stress Relieved |
Heat treated below transformation temperature after cold drawing |
Improved dimensional stability |
| +A |
Annealed |
Fully annealed after final cold drawing |
Flaring, expansion, and extensive forming |
| +N |
Normalized |
Normalized in a controlled atmosphere |
Uniform structure and improved formability |
Frequently Asked Questions
Are you a trading company or manufacturer?
We are a manufacturer, but we can also handle trading operations.
How long is your delivery time?
Generally speaking, it is 10-15 days if the goods are in stock, or 30-40 days if the goods are not in stock, depending on quantity.
Do you provide samples? Is it free or extra?
Yes, we could offer the sample for free but need payment for the cost of freight.
What are your terms of payment?
Payment ≤2000USD: 100% in advance. Payment ≥2000USD: 30% T/T in advance, balance before shipment.
