Stainless Steel Coil Tube — Seamless Tube Cold Re-Drawing (Redraw) Process Specification
1. Product Overview
The Stainless Steel Coil Tube produced through the seamless tube cold re-drawing process represents a premium-grade coil tube solution engineered for high-precision industrial applications. This product leverages an advanced secondary cold drawing operation applied to pre-formed seamless stainless steel tubes, delivering exceptional dimensional accuracy, superior surface finish, and enhanced mechanical integrity. Designed primarily as the parent tube (mother pipe) for high-end instrument tubes and EP (Electrophoretic Deposition) tube processing, this coil tube serves as the foundational material in critical manufacturing chains requiring stringent quality standards.
Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this coil tube product exemplifies the company's commitment to metallurgical excellence and process innovation in the stainless steel pipe industry. The cold re-drawing technique is a sophisticated forming process that further refines the geometry and surface characteristics of seamless tubes beyond the capabilities of initial cold drawing alone.
2. Material & Properties
2.1 Base Material Grades
- AISI 304 / SUS 304 — General-purpose austenitic stainless steel with excellent corrosion resistance
- AISI 316L / SUS 316L — Low-carbon austenitic grade with superior chloride resistance
- AISI 321 / SUS 321 — Stabilized austenitic grade for elevated temperature service
- AISI 304L / SUS 304L — Low-carbon variant for welding-sensitive applications
- AISI 316L / SUS 316L — Low-carbon variant for pharmaceutical and food-grade applications
2.2 Mechanical Properties (Typical)
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (UTS) | ≥ 520 MPa | ASTM A213 / GB/T 12771 |
| Yield Strength (0.2% Offset) | ≥ 205 MPa | ASTM A213 / GB/T 12771 |
| Elongation (in 50mm) | ≥ 40% | ASTM A213 / GB/T 12771 |
| Hardness (HBW) | ≤ 220 HBW | ASTM E10 |
| Reduction of Area | ≥ 60% | ASTM E8 |
2.3 Surface Characteristics
- Surface Roughness (Ra): ≤ 0.4 μm (post cold re-drawing)
- Surface Finish Grade: Mirror / Bright Annealed (BA) / No. 1 Annealed
- Wall Thickness Uniformity: ±0.02 mm or better
- Outer Diameter Tolerance: ±0.03 mm or better (enhanced by redraw process)
3. Specifications
| Parameter | Specification Range | Notes |
|---|---|---|
| Outer Diameter (OD) | Φ3.0 mm – Φ50.0 mm | Customizable upon request |
| Wall Thickness | 0.2 mm – 3.0 mm | Thin-wall optimized |
| Coil Length (per coil) | 100 m – 500 m | Depending on OD and WT |
| Coil Inner Diameter | Φ100 mm / Φ152 mm / Φ200 mm | Standard options |
| Material Grade | 304, 304L, 316L, 321, 310S | ASTM / GB / EN standards |
| Surface Condition | BA (Bright Annealed) / Pickled / Polished | Post-annealing finish |
| OD Tolerance | ±0.03 mm (Class 1) | Enhanced by redraw process |
| Wall Thickness Tolerance | ±0.02 mm (Class 1) | Enhanced by redraw process |
| Roundness | ≤ 0.02 mm | Post cold re-drawing |
| Coil Weight | 50 kg – 500 kg | Standard shipping configuration |
4. Manufacturing Process
The seamless tube cold re-drawing process is a multi-stage manufacturing methodology that achieves exceptional dimensional precision and surface quality in stainless steel coil tubes. The complete process flow is outlined below:
4.1 Process Flow
- Raw Material Preparation: Selection of high-purity stainless steel slabs or billets conforming to ASTM A276 / GB/T 12771 chemical composition requirements. Incoming material undergoes spectroscopic verification to ensure alloy content compliance.
- Piercing & Seamless Tube Formation: The billet is heated to approximately 1,150–1,250°C and pierced through a rotating mandrel to form a seamless hollow tube (black tube). This initial stage establishes the basic tubular geometry.
- Hot Rolling & Annealing: The pierced tube undergoes hot rolling to achieve approximate dimensions, followed by solution annealing (1,050–1,150°C) and controlled cooling to relieve residual stresses and establish the austenitic microstructure.
- Initial Cold Drawing (First Draw): The annealed tube is cold-drawn through precision-die tooling with a tungsten carbide (WC) or high-speed steel (HSS) die. This stage reduces the tube to near-final dimensions while introducing controlled work hardening. Typical cross-sectional reduction in this stage: 15–30%.
- Intermediate Annealing: To restore ductility for subsequent forming, the tube undergoes a controlled annealing cycle at 1,050–1,100°C in a protective atmosphere (argon or vacuum) to prevent oxidation. This step is critical for maintaining surface quality.
- Cold Re-Drawing (Secondary Draw) — Key Process: This is the defining operation of this product category. The tube is drawn a second time through ultra-precision tooling with extremely tight tolerances. The redraw process achieves:
- Further refinement of outer diameter and wall thickness uniformity
- Significant improvement in surface finish (reduction of drawing marks and tool impressions)
- Enhanced roundness and straightness of the tube profile
- Improved mechanical properties through controlled work hardening
- Cross-sectional reduction in this stage: 5–15%
- Final Annealing & Pickling: Post-redraw annealing (1,050–1,100°C) in protective atmosphere, followed by acid pickling (HNO₃/HF blend) to remove any residual oxide scale and achieve the desired surface finish (BA or mirror).
- Coiling & Packaging: The finished tube is coiled onto precision mandrels at controlled tension to prevent deformation, then wrapped in protective film and packaged for shipping.
4.2 Critical Process Parameters
| Parameter | Typical Value | Function |
|---|---|---|
| Die Material | Tungsten Carbide (WC-Co) | Wear resistance, surface quality |
| Drawing Speed | 0.5 – 3.0 m/s | Controlled deformation rate |
| Lubricant | Water-based / Graphite-based | Reduce friction, protect surface |
| Draw Reduction per Pass | 5% – 15% | Optimal work hardening balance |
| Annealing Temperature | 1,050 – 1,100°C | Microstructure restoration |
| Atmosphere | Argon (99.99%) / Vacuum (10⁻³ Pa) | Oxidation prevention |
5. Applications
The cold re-drawn stainless steel coil tube is engineered for the most demanding applications where dimensional precision and surface quality are non-negotiable. Primary application domains include:
5.1 High-End Instrument Tubes
- Pressure Transmitter Tubes: Precision tubing for Bourdon tube pressure gauges, capsule pressure sensors, and diaphragm pressure transmitters
- Flow Measurement: Orifice plates, Venturi tubes, and flow meter reference tubes
- Temperature Sensors: Thermowell tubing and RTD (Resistance Temperature Detector) housings
- Level Measurement: Displacer-type level gauge tubing
5.2 EP (Electrophoretic Deposition) Tube Parent Pipe
- Serves as the base substrate for electrophoretic coating processes
- Requires exceptional surface uniformity to ensure consistent EP coating thickness
- Used in automotive, aerospace, and electronics industries for corrosion-protected tubing
5.3 Additional Applications
- Medical Devices: Endoscope tubing, surgical instrument housings, implant-grade components
- Food & Beverage Industry: CIP (Clean-in-Place) tubing, sanitary process lines
- Pharmaceutical Processing: GMP-compliant fluid transfer tubing
- Precision Engineering: Hydraulic and pneumatic cylinder tubes, fuel system lines
- Electronics: Heat exchanger tubes, vacuum system components
6. Quality Certifications & Standards Compliance
6.1 Applicable Standards
| Standard | Description | Scope |
|---|---|---|
| ASTM A213 | Standard Specification for Seamless Austenitic Stainless Steel Tube | Material & Product |
| ASTM A269 | Standard Specification for Seamless and Welded Austenitic Stainless Steel Shapes for Instrumentation and Chemical Service | Instrumentation Tubes |
| GB/T 12771 | Stainless Steel Seamless Tubes for General Purpose | Chinese National Standard |
| GB/T 14976 | Stainless Steel Seamless Tubes for Fluid Transport | Fluid Transport |
| EN 10216-5 | Technical Delivery Conditions for Seamless Stainless Steel Tubes | European Standard |
| JIS G3459 | Stainless Steel Tubes for General Use | Japanese Industrial Standard |
| AMS 5510 / AMS 5513 | Aerospace Material Specifications | Aerospace Applications |
6.2 Quality Certifications
- ISO 9001:2015 — Quality Management System certification
- ISO 14001:2015 — Environmental Management System certification
- ISO/IEC 17025 — Laboratory competence for testing and calibration
- EN 10204 3.1 — Third-party inspection certificates available
- CE Marking — European Conformity for pressure equipment
- PED (Pressure Equipment Directive 2014/68/EU) — Compliance for pressure applications
- API Q1 — Quality management for oil & gas industry suppliers
6.3 Inspection & Testing Protocol
- Chemical Analysis: Optical emission spectrometry (OES) or wet chemical analysis for each heat
- Mechanical Testing: Tensile test, hardness test, and impact test per ASTM E8/E10/E23
- Dimensional Inspection: Automated ultrasonic or laser measurement for OD, WT, roundness
- Surface Inspection: Visual + automated surface profiling for roughness and defects
- Non-Destructive Testing (NDT): Eddy current (ET) and ultrasonic (UT) testing for internal defects
- Hydrostatic/Pneumatic Testing: Pressure testing at 1.5× maximum working pressure
- Intergranular Corrosion Testing: ASTM A262 Practice E (if applicable)
- Heat Treatment Verification: Metallographic examination for grain size and microstructure
7. Unique Selling Points
Precision Beyond Standard: The cold re-drawing process achieves dimensional tolerances (±0.02 mm WT, ±0.03 mm OD) that exceed standard cold-drawn tube specifications by a factor of 2–3×
Surface Excellence: Surface roughness Ra ≤ 0.4 μm eliminates the need for secondary polishing operations, reducing downstream processing costs
Process Integrity: As a seamless tube product, it contains no weld seams, ensuring uniform mechanical properties and superior fatigue resistance in cyclic loading applications
EP-Compatible Geometry: The exceptional dimensional uniformity ensures consistent electrophoretic coating thickness distribution, critical for automotive and aerospace EP applications
Instrument-Grade Readiness: Ready for direct conversion into precision instrument components without additional machining, reducing manufacturing lead time by 30–40%
Traceability: Full heat-to-heat traceability from raw material to finished coil, with complete documentation package including mill test certificates (MTC), EN 10204 3.1 certificates, and lot-specific inspection reports