Stainless Steel Seamless Coil Tube — Extrusion & Cold Drawing Process (Coil Tube)
1. Product Overview
Wenzhou Jixing Metal Materials Co., Ltd. offers a premium-grade Stainless Steel Seamless Coil Tube (Product No. 52), manufactured through a proprietary Extrusion + Cold Drawing process. This product represents the pinnacle of small- to medium-diameter seamless tube technology, combining the dimensional precision of cold drawing with the superior surface integrity achievable only through the extrusion method. The resulting coil tube (Coiltube) exhibits surface quality that significantly outperforms conventional hot-rolled piercing (Hot-Rolled Piercing) seamless tubes, making it the preferred choice for applications demanding tight tolerances, superior surface finish, and consistent wall thickness uniformity.
The seamless coil tube is delivered in coiled form, enabling efficient downstream processing, reducing material waste, and facilitating automated forming operations. This product falls under the classification of Seamless Tubes within the Forming Process manufacturing category.
2. Material & Properties
2.1 Applicable Grades
- Austenitic Grades: AISI 304 (UNS S30400), AISI 304L (UNS S30403), AISI 316 (UNS S31600), AISI 316L (UNS S31603), AISI 321 (UNS S32100), AISI 316Ti (UNS S31635)
- Super-Austenitic Grades: AISI 904L (UNS N08904), Alloy 220 (UNS N08020), Alloy C-276 (UNS N10276)
- Other Grades: AISI 310S (UNS S31008), AISI 430 (UNS S43000), Custom Alloy Compositions upon request
2.2 Mechanical Properties (Typical, Annealed Condition)
- Tensile Strength (Rm): 520–750 MPa (depending on grade)
- Yield Strength (Rp0.2): 205–310 MPa
- Elongation (A50mm): ≥ 40%
- Hardness: ≤ 220 HV (annealed condition)
2.3 Surface Quality
A defining characteristic of this product is its exceptional surface finish. The extrusion + cold drawing process yields surface roughness values (Ra) as low as 0.4–0.8 μm in the annealed condition, and ≤ 0.2 μm achievable through final cold drawing. This represents a substantial improvement over hot-rolled piercing tubes, which typically exhibit Ra values of 3.2–6.3 μm. The process eliminates surface defects such as scale, decarburization, and oxide inclusions inherent to hot working.
3. Technical Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Product Type | Seamless Stainless Steel Coil Tube | — |
| Manufacturing Process | Extrusion + Cold Drawing (Seamless) | — |
| Outer Diameter (OD) | Φ3.0 – Φ108 mm | ASTM A511 / ASME SA-511 |
| Wall Thickness (WT) | 0.3 – 6.0 mm | ASTM A511 / ASME SA-511 |
| OD Tolerance | ±0.05 mm to ±0.10 mm | ASTM A511 Class 1 |
| WT Tolerance | ±0.02 mm to ±0.05 mm | ASTM A511 Class 1 |
| Surface Roughness (Ra) | 0.4 – 0.8 μm (Annealed); ≤ 0.2 μm (Cold Drawn) | ASTM A511 |
| Surface Finish Options | No. 1, 2B, BA (Bright Annealed), Mirror (4K/8K) | ASTM A480 |
| Delivery Condition | Annealed (Solution Annealed) | — |
| Coil Weight | 500 – 3,000 kg per coil | — |
| Applicable Standards | ASTM A511, ASME SA-511, EN 10217-7, JIS G3459 | — |
| Testing Standards | ASTM A999, ASTM E10, ASTM A240 | — |
| Applicable Grades | 304, 304L, 316, 316L, 321, 310S, 904L, Alloy 220, C-276 | ASTM A480 |
4. Manufacturing Process
4.1 Process Flowchart
- Raw Material Preparation: High-purity stainless steel ingots or billets are selected and subjected to spectroscopic analysis to verify chemical composition compliance with the specified grade requirements.
- Extrusion (Hot Extrusion): The prepared billet is heated to a temperature range of 1,050–1,250 °C and extruded through a calibrated die to produce a seamless tube blank (extruded tube). This step establishes the initial tube geometry while maintaining a closed, continuous cross-section without any weld seam.
- Pickling & Descaling: The extruded tube is chemically pickled and mechanically descaled to remove oxide layers formed during the hot extrusion process, ensuring a clean substrate for subsequent cold working.
- Cold Drawing (Cold Pulling): The descaled tube is drawn through precision-diameter dies using either a mandrel-drawn (Plug Drawing) or cap-drawn (Cap Drawing) technique. This step achieves the final dimensional accuracy, wall thickness uniformity, and superior surface finish. Multiple drawing passes may be employed to achieve extremely tight tolerances.
- Intermediate Annealing (if required): For tubes requiring multiple drawing passes, intermediate annealing at 1,050–1,150 °C is performed to relieve work-hardening and restore ductility between passes.
- Final Annealing (Solution Annealing): The cold-drawn tube is solution-annealed at the appropriate temperature (typically 1,020–1,120 °C depending on grade) followed by rapid water quenching to dissolve carbide precipitates and achieve the desired microstructure and corrosion resistance.
- Final Pickling & Passivation: Post-annealing pickling removes any residual oxide, and passivation treatment forms a stable chromium oxide layer to enhance corrosion resistance.
- Dimensional Inspection & Non-Destructive Testing (NDT): Each tube undergoes comprehensive dimensional verification, hydrostatic pressure testing, and surface inspection (visual and/or automated).
- Coiling: The qualified tube is wound into coils of specified weight and diameter, protected with appropriate packaging.
4.2 Process Advantages — Extrusion + Cold Drawing vs. Hot-Rolled Piercing
| Performance Parameter | Extrusion + Cold Drawing | Hot-Rolled Piercing |
|---|---|---|
| Surface Roughness (Ra) | 0.4 – 0.8 μm | 3.2 – 6.3 μm |
| Dimensional Tolerance (OD) | ±0.05 – ±0.10 mm | ±0.30 – ±0.50 mm |
| Wall Thickness Uniformity | ≤ ±0.02 mm | ≤ ±0.15 mm |
| Minimum Achievable Diameter | Φ3.0 mm | Φ20 mm (practical limit) |
| Minimum Achievable Wall Thickness | 0.3 mm | 1.5 mm (practical limit) |
| Surface Defects (Scale, Inclusions) | None (clean surface) | Present (requires additional grinding) |
| Microstructural Uniformity | Excellent (homogeneous grain structure) | Non-uniform (deformation banding) |
5. Applications
The combination of superior surface quality, tight dimensional tolerances, and seamless construction makes this product ideal for the following high-performance applications:
- Precision Instrumentation: Capillary tubes, pressure sensor housings, and analytical instrument tubing requiring leak-tight, corrosion-resistant, and dimensionally stable components.
- Medical & Pharmaceutical Equipment: Surgical instrument tubing, dialysis machine components, pharmaceutical process piping, and autoclavable tubing systems where surface finish and biocompatibility are critical.
- Food & Beverage Processing: CIP (Clean-in-Place) and SIP (Sterilize-in-Place) piping systems, sanitary-grade tubing, and food-grade process lines requiring hygienic surface finishes.
- Semiconductor & Electronics: Ultra-pure gas delivery lines, vacuum chamber components, and cleanroom-compatible tubing for semiconductor manufacturing facilities.
- Chemical & Petrochemical Industry: Corrosion-resistant heat exchanger tubes, reactor internals, and process piping for aggressive chemical environments.
- Automotive & Aerospace: Precision exhaust system components, fuel lines, hydraulic tubing, and structural tubing for high-performance and aerospace applications.
- Downstream Coil Processing: The coil format enables efficient coil-to-tube conversion, coil slitting, coil bending, and automated tube processing with minimal material loss.
6. Quality Certifications & Testing
6.1 Factory Certifications
- ISO 9001:2015 — Quality Management System
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health & Safety Management System
- EN 10204 3.1 — Material Testing Certificate (MTC)
- PED (Pressure Equipment Directive) 2014/68/EU — Compliance for pressure equipment applications
- ASME / NACE — Compliance for pressure vessel and piping applications
6.2 Inspection & Testing Protocols
- Chemical Analysis: Optical emission spectroscopy (OES) and direct current arc spectroscopy (DC-AES) for full elemental composition verification per ASTM A751.
- Mechanical Testing: Tensile testing per ASTM A380; hardness testing per ASTM E10 (Vickers) or ASTM E18 (Rockwell B).
- Hydrostatic Pressure Testing: Per ASTM A511, with test pressure calculated as: P = 2 × S × T / D, where S = allowable stress, T = wall thickness, D = outer diameter.
- Non-Destructive Testing (NDT): Eddy current testing (ECT) per ASTM A999 for surface and near-surface defect detection; ultrasonic testing (UT) for internal defect verification.
- Dimensional Inspection: Automated optical gauging for OD, wall thickness, and roundness; laser scanning for coil profile verification.
- Surface Quality Inspection: Visual inspection under controlled lighting; surface roughness measurement per ASTM E1927; intergranular corrosion testing per ASTM A262 Practice E (for grades susceptible to sensitization).
- Intergranular Corrosion Testing: ASTM A262 Practice A (acid immersion) or Practice E (ASTM A911) for verification of carbide precipitation resistance.
- Crack Detection Testing: ASTM A999 Eddy Current Testing for detection of longitudinal and transverse cracks.
6.3 Traceability & Documentation
Each coil is accompanied by a comprehensive Mill Test Certificate (MTC) conforming to EN 10204 3.1, providing full traceability from raw material lot number through all manufacturing stages. Individual coil identification is maintained through laser-marked or stamped traceability codes, enabling complete genealogy tracking throughout the supply chain.
7. Unique Selling Points
Superior Surface Quality: The extrusion + cold drawing process delivers surface roughness (Ra) values up to 8–15 times better than conventional hot-rolled piercing tubes, eliminating the need for secondary grinding or polishing in most applications.
Unmatched Dimensional Precision: Achieving OD tolerances of ±0.05 mm and wall thickness tolerances of ±0.02 mm, this process enables direct use in precision assembly applications without additional machining.
Optimized for Small & Medium Diameters: The process is specifically