Precision-Grade Stainless Steel Coil Tube (Coiltube) — Wenzhou Jixing Metal Materials Co., Ltd
1. Product Overview
The Precision-Grade Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a high-tolerance, cold-worked tubular product engineered specifically for applications demanding exceptional dimensional accuracy and surface integrity. Classified under the geometric parameter tolerance grades of the company's product specification system (Product No. 39), this precision-grade coil tube delivers an outer diameter (OD) tolerance of ±0.5% and a wall thickness (WT) tolerance of ±5%, positioning it as the premier choice for compression fittings (compression-type tube fittings) and critical precision assembly operations.
Unlike standard-grade coil tubes, the Precision-Grade variant undergoes enhanced cold drawing and multi-stage calibration processes to achieve sub-millimeter dimensional consistency along the entire coil length. This ensures reliable interference fit performance with compression fittings, eliminates assembly rework, and guarantees leak-free performance in high-pressure and hygienic systems.
2. Material & Properties
2.1 Base Material
The coil tube is fabricated from austenitic stainless steel grades conforming to international standards, with primary availability in the following compositions:
- ASTM A269 / AMS 5600 — Type 304 (1.4301): General-purpose corrosion resistance; suitable for food-grade, chemical, and cryogenic applications.
- ASTM A269 / AMS 5510 — Type 316 (1.4401): Enhanced pitting and crevice corrosion resistance due to 2.0–3.0% molybdenum content; ideal for marine and pharmaceutical environments.
- ASTM A269 — Type 316L (1.4404): Low-carbon variant (C ≤ 0.03%) for superior weldability and resistance to intergranular corrosion in sensitized zones.
- ASTM A269 — Type 321 (1.4541): Titanium-stabilized grade for elevated-temperature service up to 870 °C.
2.2 Mechanical Properties (Representative — Type 304, Cold-Drawn)
| Property | Unit | Minimum Value |
|---|---|---|
| Tensile Strength (UTS) | MPa | ≥ 520 |
| Yield Strength (0.2% Offset) | MPa | ≥ 205 |
| Elongation (A50mm) | % | ≥ 40 |
| Hardness (HV10) | HV | ≤ 210 |
| Thermal Conductivity (20 °C) | W/(m·K) | 14.9 |
| Modulus of Elasticity | GPa | 193 |
2.3 Surface Finish
The Precision-Grade coil tube is supplied with a cold-drawn surface finish achieving a surface roughness of Ra ≤ 0.8 μm on the outer diameter and Ra ≤ 0.4 μm on the inner bore (upon request, electrolytic polishing to Ra ≤ 0.2 μm is available for sanitary applications). The precision cold-drawing process eliminates scale, oxide inclusions, and surface defects that would compromise fitting engagement.
3. Technical Specifications
3.1 Dimensional Tolerances — Precision Grade
| Parameter | Tolerance Class | Specification | Reference Standard |
|---|---|---|---|
| Outer Diameter (OD) | Precision (精密级) | ±0.5% of nominal | ASTM A269 / EN 10217-7 |
| Wall Thickness (WT) | Precision (精密级) | ±5% of nominal | ASTM A269 / EN 10217-7 |
| Coil Diameter | Standard | ±20 mm | Company Specification |
| Straightness (per meter) | Precision | ≤ 1.0 mm/m | EN 10217-7 |
| Roundness (Ovality) | Precision | ≤ 0.5% of nominal OD | EN 10217-7 |
| Length (Cut-to-Length) | Precision | ±1.0 mm | Company Specification |
3.2 Available Size Ranges
| Parameter | Range |
|---|---|
| Outer Diameter (OD) | 3.0 mm – 50.8 mm (1/8" – 2") |
| Wall Thickness (WT) | 0.30 mm – 3.00 mm |
| Coil Length | 15 m – 120 m (per coil) |
| Coil Inner Diameter | 150 mm – 600 mm |
3.3 Tolerance Comparison: Standard vs. Precision Grade
| Grade | OD Tolerance | WT Tolerance | Typical Application |
|---|---|---|---|
| Standard Grade | ±1.0% – ±1.5% | ±10% – ±15% | Structural, general fluid conveyance |
| High Grade | ±0.8% | ±8% | Hydraulic systems, process piping |
| Precision Grade (精密级) | ±0.5% | ±5% | Compression fittings, precision assembly |
4. Manufacturing Process
4.1 Process Flow
- Slit Coil Preparation: Hot-rolled stainless steel strip (slit coil) is inspected for surface quality and compositional conformity via optical emission spectroscopy (OES) and positive material identification (PMI).
- Forming (Roll Forming): The strip is passed through a series of precision rollers to form the initial tube geometry with controlled reduction ratios (typically 3:1 to 5:1 per pass).
- Welding (TIG / Laser): Seamless weld formation via Transferred Arc TIG welding or laser welding, with internal nitrogen shielding to minimize weld oxide formation. Weld penetration is verified by inline ultrasonic testing (UT).
- Heat Treatment (Solution Annealing): Post-weld solution annealing at 1050–1100 °C followed by controlled cooling to restore austenitic microstructure and relieve residual stresses.
- Precision Cold Drawing: The coil tube is drawn through a series of tungsten carbide (WC) dies with progressively tighter tolerances. This multi-pass cold working is the critical differentiator of the Precision Grade, achieving the ±0.5% OD and ±5% WT specifications.
- Intermediate Annealing: Where necessary, intermediate annealing cycles (850–950 °C) are performed between drawing passes to prevent work hardening and maintain ductility.
- Coiling: The precision-drawn tube is coiled onto a mandrel at controlled tension to prevent deformation or kinking.
- Final Inspection & Certification: 100% dimensional verification via laser micrometry; sample destructive testing (tensile, impact, hardness); chemical analysis confirmation.
4.2 Critical Process Controls for Precision Grade
- Die Calibration: Tungsten carbide dies are calibrated every 500 meters of production to ensure dimensional stability.
- In-Process Monitoring: Continuous laser OD and wall thickness gauges with ±0.01 mm resolution provide real-time feedback to the drawing line PLC.
- Temperature Control: Drawing oil temperature maintained at 40–55 °C to ensure consistent lubrication and prevent thermal drift in dimensional accuracy.
- Coil Tension Control: Precision tensioning system (±5 N tolerance) prevents coil-set distortion that could compromise OD roundness.
5. Applications
5.1 Primary Application Domains
- Compression Fitting Systems: The ±0.5% OD tolerance ensures uniform engagement of the ferrule (compression ring) against the tube OD, providing consistent clamping force and leak-free sealing. This is the definitive requirement for flareless compression fittings (e.g., Swagelok, Parker, Wenglor systems).
- Precision Instrumentation & Analytical Equipment: Gas chromatography (GC), mass spectrometry (MS), and flow cytometry systems require tubing with negligible dimensional variation to ensure reproducible flow rates and sample delivery.
- Medical & Pharmaceutical Piping: Clean-in-place (CIP) and sterilize-in-place (SIP) systems, bioreactor feed lines, and pharmaceutical transfer lines where dimensional consistency ensures proper fitting and eliminates dead legs.
- Aerospace Fuel & Hydraulic Lines: High-pressure hydraulic and fuel systems where fitting integrity under vibration and thermal cycling is mission-critical.
- Semiconductor Cleanroom Piping: Ultra-high purity (UHP) gas delivery systems (N₂, Ar, He) requiring surface finish and dimensional precision to minimize particle generation.
- Cryogenic Systems: Liquefied natural gas (LNG), liquid oxygen (LOX), and liquid nitrogen (LIN) transfer lines operating at temperatures as low as −196 °C.
5.2 Why Precision Grade is Mandatory for Compression Fittings
Compression fittings rely on a precise interference relationship between the tube outer diameter and the ferrule bore. A deviation exceeding ±0.5% in OD results in either insufficient clamping force (leakage) or excessive crimping pressure (tube deformation, reduced burst strength, ferrule galling). The Precision Grade specification of ±0.5% OD and ±5% WT is the industry-recognized minimum tolerance class that ensures reliable performance across the full range of fitting sizes (1/8" through 2").
6. Quality Certifications & Testing
6.1 Applicable Standards & Certifications
- ASTM A269 / A269M: Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubes for High-Pressure and High-Temperature Applications
- EN 10217-7: Non-alloy and Alloy Steel Tubes for Mechanical and Technical Purposes — Welded Tubes — Technical Delivery Conditions (TDC) — Precision Tubes
- ISO 4200: Metallic materials — Non-alloy and stainless steel tubes — Tolerances on dimensions and geometry
- ASME B31.3: Process Piping — Material requirements and pressure design criteria
- ASME BPE: Bioprocessing Equipment — for pharmaceutical-grade applications
- ISO 9001:2015: Quality Management System certification for the manufacturing facility
- ISO 14001:2015: Environmental Management System
- CE Marking: Conformity with European Pressure Equipment Directive (PED) 2014/68/EU
6.2 Testing Protocol
| Test Method | Standard | Frequency | Acceptance Criteria |
|---|---|---|---|
| Dimensional Verification (OD, WT, Roundness) | ASTM E1661 / Company SOP | 100% inline | Within ±0.5% OD, ±5% WT |
| Hydrostatic Pressure Test | ASTM A269 | 100% per coil | No leakage at 1.5× design pressure for 10 s |
| Chemical Composition (OES) | ASTM E415 | Per heat/lot | Within ASTM grade specification |
| Tensile Test | ASTM E8/E8M | Per heat/lot | ≥ 520 MPa UTS, ≥ 40% elongation |
| Flattening Test | ASTM A269 | Per heat/lot | No cracking at specified reduction |
| Surface Roughness (Ra) | ASTM E1926 | Sample per coil | OD: Ra ≤ 0.8 μm; ID: Ra ≤ 0.4 μm |
| Intergranular Corrosion | ASTM A269 (Test H) | Per heat (316L, 321) | No intergranular attack |
| Weld Penetration (UT) | ASTM E164 | 100% inline | Full penetration, no voids |
6.3 Traceability & Documentation
Each coil of Precision-Grade Stainless Steel Coil Tube is accompanied by a comprehensive Mill Test Certificate (MTC) conforming to EN 10204 3.1, providing full traceability including: heat number, chemical composition, mechanical test results, dimensional verification records, and manufacturing process parameters. QR-coded lot identification enables digital traceability throughout the supply chain.
7. Unique Selling Points
- Industry-Leading Tolerance Consistency: The ±0.5% OD tolerance is achieved through multi-pass cold drawing with inline laser verification, exceeding the