Stainless Steel Coil Tube (Coil Tube) — Product Technical Specification
1. Product Overview
Stainless Steel Coil Tube (also known as Coil Pipe or Coiled Tubing) refers to a continuous-length hollow stainless steel section wound onto a coil or spool for storage, transportation, and processing. Unlike cut-length pipes, coil tubes are manufactured in uninterrupted lengths, enabling downstream users to draw the material continuously through forming, bending, welding, and cutting operations without the need for butt-joint splicing. This continuous geometry significantly reduces material waste, eliminates inter-segment welding defects, and improves overall manufacturing efficiency.
The product is supplied by Wenzhou Jixing Metal Materials Co., Ltd, a specialized manufacturer in the stainless steel pipe and tubing sector. The coil tube is produced using a dedicated Coil Tube Making Machine (Coil Tubing Production Line), which integrates continuous forming, welding, sizing, and coiling processes into a single integrated production cycle. The machine learning and operational optimization of this coil tube machinery have contributed to enhanced dimensional consistency, improved weld integrity, and reduced production cycle times.
2. Material & Properties
2.1 Common Alloy Grades
- AISI 304 / ASTM 304 (UNS S30400) — Austenitic stainless steel; excellent general corrosion resistance; non-magnetic in annealed condition; widely used in food processing, chemical, and architectural applications.
- AISI 316 / ASTM 316 (UNS S31600) — Molybdenum-bearing austenitic grade; superior resistance to pitting and crevice corrosion in chloride-containing environments; preferred for marine, pharmaceutical, and chemical processing applications.
- AISI 316L / ASTM 316L (UNS S31603) — Low-carbon variant of 316; enhanced resistance to sensitization during welding; suitable for high-temperature and welded structural applications.
- AISI 321 / ASTM 321 (UNS S32100) — Titanium-stabilized austenitic grade; excellent resistance to intergranular corrosion at elevated temperatures (up to 870 °C / 1600 °F).
- AISI 310 / ASTM 310 (UNS S31000) — High-temperature austenitic grade; outstanding oxidation resistance and thermal shock resistance up to 1150 °C (2100 °F).
- AISI 430 / ASTM 430 (UNS S43000) — Ferritic stainless steel; lower-cost alternative with adequate corrosion resistance; magnetic; used in automotive and appliance applications.
2.2 Key Mechanical Properties (Typical Values for Grade 304 in Annealed Condition)
- Tensile Strength (UTS): ≥ 515 MPa (74,700 psi)
- Yield Strength (0.2% Offset): ≥ 205 MPa (29,700 psi)
- Elongation at Break: ≥ 40%
- Hardness (Brinell): ≤ 201 HB
- Density: 8.0 g/cm³ (0.29 lb/in³)
- Thermal Conductivity: 16.3 W/(m·K) at 100 °C
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /K (10–100 °C)
- Maximum Service Temperature: 870 °C (1600 °F)
3. Specifications
| Parameter | Specification Range |
|---|---|
| Outer Diameter (OD) | 6.0 mm – 50.8 mm (1/4" – 2") |
| Wall Thickness | 0.3 mm – 3.0 mm (0.012" – 0.118") |
| Inner Diameter (ID) | 5.0 mm – 47.8 mm (0.20" – 1.88") |
| Coil Length (Continuous) | 50 m – 300 m (164 ft – 984 ft), customizable |
| Coil Weight | 200 kg – 500 kg (441 lb – 1,102 lb) per coil |
| Surface Finish | No. 1 (Cold Rolled & Annealed), 2B, BA (Bright Annealed), No. 4 (Brushed), HL (Hairline), Mirror (8K) |
| End Form | Plain (as-formed) or Beveled / Threaded (upon request) |
| Dimensional Tolerance (OD) | ±0.1 mm – ±0.25 mm (per ASTM A269 / EN 10217) |
| Dimensional Tolerance (Wall) | ±10% of nominal thickness (minimum ±0.05 mm) |
| Standard References | ASTM A269, ASTM A554, EN 10217-7, GB/T 12771, JIS G3459 |
| Available Grades | 304, 304L, 316, 316L, 321, 310, 310S, 430, 904L, 2205 (Duplex) |
| Welding Method | Automatic Submerged Arc Welding (SAW) / TIG Welding with Internal Gas Shielding |
| Heat Treatment | Solution Annealing (1050–1150 °C followed by water quench) or Stress Relief |
4. Manufacturing Process
4.1 Process Flow
- Coil Uncoiling & Feeding: Cold-rolled stainless steel strip (coil) is uncoiled from the supply reel and fed through the forming line at controlled tension. Strip width is matched to the target pipe OD.
- Edge Preparation: The strip edges are trimmed and cleaned to remove scale, burrs, and surface contaminants that could compromise weld quality.
- Forming (Roll Forming): A series of precision dies (forming rolls) progressively bends the flat strip into a semi-circular or near-circular profile. Each roll pair applies incremental deformation to avoid wrinkling or tearing.
- Welding: The formed semi-circular strip is fed into the welding station. Automatic Submerged Arc Welding (SAW) is employed with internal inert gas shielding (typically Argon or Argon/Helium mixtures). The weld current and speed are precisely controlled to ensure full-penetration weld integrity. For high-purity applications, TIG (Tungsten Inert Gas) welding with internal gas purge is utilized.
- Weld Inspection: The weld seam is immediately inspected using eddy current testing (ECT) or ultrasonic testing (UT) to detect porosity, lack of fusion, or undercut defects. Defective sections are automatically marked for removal.
- Sizing: The welded pipe passes through a sizing die set (typically 3–4 passes) to achieve precise final OD and wall thickness within tolerance. This process also ensures roundness and ovality compliance.
- Cooling: The pipe is cooled via air blast or water quench to bring the weld zone back to ambient temperature, preventing microstructural degradation.
- Coiling: The continuous pipe is wound onto a steel or wooden coil/spool at controlled tension to prevent kinking or deformation. The coil is then secured with steel bands or straps.
- Post-Processing (Optional): Depending on application requirements, the coil tube may undergo solution annealing, pickling and passivation (to remove welding discoloration and form a protective chromium oxide layer), or surface finishing.
4.2 Key Process Parameters
- Forming Roll Material: Hardened alloy steel (HRC 58–62) with surface coating (e.g., diamond-like carbon, DLC) for extended tool life and reduced surface drag.
- Weld Current: 180–350 A (adjustable based on strip thickness and grade)
- Production Speed: 5–20 m/min (variable by diameter and wall thickness)
- Internal Gas Purge Flow Rate: 2–8 L/min (to ensure a clean, oxide-free weld root)
5. Applications
5.1 Primary End-Use Industries
- Oil & Gas Industry: Coiled tubing for well intervention, acidizing, nitrogen injection, and hydraulic fracturing operations. The continuous-length format eliminates the need for in-well splices.
- Chemical & Pharmaceutical Processing: Process piping, heat exchanger tubes, and reactor internals requiring corrosion-resistant, hygienic surfaces.
- Food & Beverage Industry: Hygienic-grade tubing (BA or electropolished finish) for dairy processing, brewing, and food-grade fluid transfer systems.
- Automotive Industry: Exhaust system components, fuel lines, brake lines, and sensor housings. The coil format enables high-volume automated stamping and bending operations.
- Construction & Architecture: Structural tubing, handrails, balustrades, and decorative applications where continuous forming eliminates visible butt joints.
- Medical Devices: Implant-grade tubing (316L VM grade) for orthopedic instruments, surgical tools, and diagnostic equipment.
- Aerospace: Fuel lines, hydraulic lines, and exhaust components requiring high strength-to-weight ratios and fatigue resistance.
- Energy Sector: Solar thermal collector tubes, heat exchanger tubes, and geothermal well tubing.
5.2 Advantages of Coil Format Over Cut-Length Pipe
- Eliminates butt-weld joints, reducing potential failure points by up to 100% for equivalent length
- Material utilization rate exceeds 95% (versus 85–90% for cut-length pipe with end-trim waste)
- Enables continuous, high-speed downstream processing (bending, welding, cutting) without stoppage for pipe replacement
- Reduced inventory and logistics costs due to compact coil storage and transport
- Consistent metallurgical properties along the entire length (homogeneous microstructure)
6. Quality Certifications & Compliance
6.1 International Standards Compliance
- ASTM A269 / A269M: Standard Specification for Seamless and Wrought Stainless Steel Pipe, Tubing, and Shapes for Chemical and Allied Applications
- ASTM A554 / A554M: Standard Specification for Seamless and Welded Austenitic Stainless Steel Electric-Resistance-Welded Tube
- EN 10217-7: Heat-resistant, creep-resistant, and high-strength steels — Welded tubes for mechanical and technical use — Part 7: Non-heat-treated stainless steel tubes
- GB/T 12771: Chinese National Standard for Stainless Steel Seamless Pipes and Tubes for Fluid Transport
- JIS G3459: Japanese Industrial Standard for Stainless Steel Seamless Tubes
- ASME B31.3: Process Piping Code (for design and installation compliance)
6.2 Quality Assurance System
- ISO 9001:2015: Quality Management System certification ensuring consistent product quality and continuous improvement
- ISO 14001:2015: Environmental Management System certification for sustainable manufacturing practices
- ISO/IEC 17025: Laboratory accreditation for in-house testing and calibration capabilities
- PE/TPED (Pressure Equipment Directive): Compliance for pressure-containing applications in European markets
- NACE MR0175 / ISO 15156: Compliance for materials used in oil and gas environments (sulfide stress cracking resistance)
6.3 Testing & Inspection Protocols
| Test Type | Method | Frequency | Purpose |
|---|---|---|---|
| Hydrostatic Test | Internal water pressure at 1.5× maximum working pressure | 100% (every coil) | Leak detection and weld integrity verification |
| Eddy Current Testing (ECT) | Non-destructive electromagnetic inspection of weld seam | 100% (continuous online) | Weld defect detection (porosity, cracks, lack of fusion) |
| Ultrasonic Testing (UT) | High-frequency sound wave penetration testing | 100% or per customer specification | Internal and surface defect detection |
| Dimensional Inspection | Laser OD gauge, ultrasonic wall thickness gauge, roundness measurement | 100% (continuous online) | Conformance to dimensional tolerances |
| Chemical Composition Analysis | Optical Emission Spectroscopy (OES) or X-ray Fluorescence (XRF) | Per heat lot | Alloy grade verification |
| Mechanical Testing | Tensile, hardness, and impact testing per ASTM E8/E10 | Per heat lot or per customer request | Verification of mechanical properties |
| Corrosion Testing | Pitting corrosion test (ASTM G48), intergranular corrosion test (ASTM A262 Practice E) | Per customer request or qualification | Corrosion resistance verification |
| Visual & Surface Inspection | Magnified visual examination (5×–10×) | 100% | Surface defect detection (dents, scratches, discoloration) |
6.4 Mill Test Certificates (MTC)
Each production lot is accompanied by a Mill Test Certificate (MTC) conforming to EN 10204 (Certificate Type 3.1 or 3.2 as required). The MTC documents chemical composition, mechanical test results, dimensional measurements, heat treatment records, and non-destructive testing results, providing full traceability from raw material to finished product.