Stainless Steel Coil Tube (Coil Tube) — Technical Specification
Product Overview
Stainless steel coil tubes (also referred to as coil tubing or coiled tubing) are continuous-length tubular products formed into helical coil configurations during manufacturing. These products are produced by Wenzhou Jixing Metal Materials Co., Ltd, a specialized manufacturer with extensive expertise in precision metal tube fabrication. Coil tubes are distinguished from standard straight tubes by their continuous, spring-like geometry, which provides inherent flexibility, compact storage, and enhanced fatigue resistance under cyclic loading conditions.
The development of domestic coil tube technology and manufacturing equipment represents a significant advancement in China's metallurgical and materials engineering sector. Through systematic research and development programs, domestic manufacturers have achieved parity with international standards in coil tube production capability, encompassing both material science innovation and precision forming equipment design. This product line reflects the culmination of decades of accumulated engineering knowledge in stainless steel metallurgy, tube rolling, and coiling technology.
Material Composition & Mechanical Properties
Stainless steel coil tubes are manufactured from austenitic, ferritic, or duplex stainless steel grades, selected based on the specific application requirements regarding corrosion resistance, mechanical strength, and temperature tolerance.
Commonly Used Grades
- Austenitic Grades: AISI 304 (UNS S30400), AISI 304L (UNS S30403), AISI 316 (UNS S31600), AISI 316L (UNS S31603), AISI 321 (UNS S32100), AISI 321H (UNS S32109), AISI 310S (UNS S31008)
- Ferritic Grades: AISI 430 (UNS S43000), AISI 444 (UNS S44400)
- Duplex Grades: 2205 (UNS S31803/S32205), 2507 (UNS S32750/S32760)
- Custom Alloy Grades: Available upon specification for specialized high-performance applications
Mechanical Properties (Typical Values for Grade 316L in Annealed Condition)
- Tensile Strength (Rm): ≥ 520 MPa (75,400 psi)
- Yield Strength (Rp0.2): ≥ 205 MPa (29,700 psi)
- Elongation (A5): ≥ 35%
- Hardness (HV): ≤ 220
- Corrosion Resistance: Excellent resistance to pitting (Pitting Resistance Equivalent Number, PREN ≥ 24), crevice corrosion, and intergranular corrosion
- Operating Temperature Range: −196°C to +650°C (−320°F to +1,202°F) for austenitic grades
Chemical Composition (Grade 316L — Typical)
| Element | Specification (wt%) |
|---|---|
| Carbon (C) | ≤ 0.030 |
| Chromium (Cr) | 16.00 – 18.00 |
| Nickel (Ni) | 10.00 – 14.00 |
| Molybdenum (Mo) | 2.00 – 3.00 |
| Iron (Fe) | Balance |
| Phosphorus (P) | ≤ 0.035 |
| Sulfur (S) | ≤ 0.030 |
| Silicon (Si) | ≤ 0.75 |
| Manganese (Mn) | ≤ 2.00 |
Dimensional Specifications
| Parameter | Specification Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 3.18 mm – 168.3 mm (1/8" – 6-5/8") | ASTM A269 / A213 |
| Wall Thickness | 0.51 mm – 12.70 mm (0.020" – 0.500") | ASTM A269 / A213 |
| Coil Diameter | 300 mm – 1,200 mm (12" – 48") | Manufacturer standard |
| Coil Length (per coil) | 15 m – 300 m (50 ft – 1,000 ft) | Customizable |
| OD Tolerance | ± 0.05 mm (for OD ≤ 10 mm); ± 0.5% (for OD > 10 mm) | ASTM A269 |
| Wall Thickness Tolerance | ± 10% (minimum ± 0.05 mm) | ASTM A269 |
| Surface Finish | 2B (Cold Rolled and Annealed), BA (Bright Annealed), No. 4, No. 8 Mirror, Custom | ASTM A480 |
| End Condition | Plain end, Beveled end, Welded cap, Threaded | Per customer specification |
| Coil Turn Spacing | 0.5 mm – 5.0 mm (adjustable) | Manufacturer standard |
| Maximum Residual Stress | ≤ 150 MPa (post-annealing) | Internal specification |
Manufacturing Process
The production of stainless steel coil tubes involves a multi-stage manufacturing process that integrates metallurgical processing, precision forming, and quality control at each stage. The process flow is as follows:
1. Raw Material Preparation
- Hot-rolled stainless steel strip or seamless pipe stock is procured from certified mills
- Incoming material undergoes spectrographic analysis (OES — Optical Emission Spectroscopy) to verify chemical composition
- Dimensional inspection of raw material using laser measurement systems
2. Pickling and Descaling
- Acid pickling (nitric-hydrofluoric acid blend) to remove mill scale and oxide layers
- Passivation treatment to restore passive chromium oxide film
- Ultrasonic cleaning for critical applications requiring low surface contamination
3. Forming and Welding
- For welded coil tube: Strip is formed into tubular shape via roll-forming machines, followed by longitudinal welding using TIG (Tungsten Inert Gas) or laser welding processes
- For seamless coil tube: Hot-rolled seamless pipe is cold-drawn or cold-rolled to final dimensions
- Weld seam inspection via eddy current testing (ECT) or ultrasonic testing (UT)
4. Heat Treatment
- Solution annealing at 1,020°C – 1,150°C (1,868°F – 2,094°F) followed by rapid water quenching
- Stress-relief annealing at 600°C – 800°C for spring-set recovery
- Precipitation hardening for precipitation-hardening grades (e.g., 17-4 PH)
5. Cold Forming and Coiling
- Continuous coiling using precision coil-forming machines with controlled bending radius
- Bending radius is maintained at a minimum of 3× OD (3D) to prevent ovalization and wall thinning
- Online dimensional monitoring during coiling to ensure coil diameter consistency
- Coil set adjustment to achieve desired spring-back characteristics
6. Surface Finishing
- Electropolishing for ultra-smooth surface finish (Ra ≤ 0.4 μm)
- Passivation to enhance corrosion resistance
- Surface inspection using profilometry and visual examination
7. Final Quality Control
- Hydrostatic pressure testing (typically 2–5× design pressure) to verify structural integrity
- Dimensional verification using CMM (Coordinate Measuring Machine) and laser scanners
- Non-destructive testing (NDT) including ECT, UT, and magnetic particle inspection (MPI)
- Chemical re-verification and mechanical property testing on representative samples
Applications
Stainless steel coil tubes find extensive application across multiple industries due to their superior combination of corrosion resistance, mechanical strength, flexibility, and hygienic properties:
Process Industries
- Heat exchangers and condensers (shell-and-tube, plate-fin configurations)
- Refrigeration and air conditioning (HVAC — Heating, Ventilation, and Air Conditioning) systems
- Chemical processing plants (reactors, distillation columns, piping systems)
- Oil and gas industry (subsea pipelines, chemical injection systems, wellhead equipment)
Food and Pharmaceutical Industries
- Dairy processing equipment (CIP — Clean-in-Place systems, heat exchangers)
- Beverage processing (brewing, carbonated drink systems)
- Pharmaceutical manufacturing (sterile fluid transfer, bioreactor piping)
- Food-grade hygienic piping systems compliant with FDA 21 CFR
Energy Sector
- Solar thermal collectors (evacuated tube collectors)
- Geothermal energy systems (heat exchangers, well completion tubing)
- Nuclear industry (fuel cladding, heat transfer components)
- Power generation (boiler tubes, condensers, superheaters)
Automotive and Transportation
- Automotive exhaust systems (catalytic converter substrates)
- Brake lines and fuel delivery systems
- Railway braking systems
- Marine applications (ballast systems, propulsion cooling)
Medical Devices
- Surgical instrument tubing
- Endoscopic equipment components
- Implantable device housings
- Dialysis machine tubing
Quality Certifications & Standards Compliance
Applicable Standards
- ASTM A269: Standard Specification for Seamless and Welded Austenitic Stainless Steel Tube for Chemical and Heat-Transfer Applications
- ASTM A213: Standard Specification for Seamless Austenitic Chromium-Nickel Stainless Steel Heat-Exchanger and Heat-Transfer Tube
- ASTM A778: Standard Specification for Stainless Steel Tubular Products for General Application
- EN 10216-5: Non-alloy and alloy steel tubes for mechanical, thermal and other technical uses — Part 5: Dimensional tolerances and special characteristics for austenitic tubes
- ISO 4200: Non-ferrous metals and alloys — Tubes and pipes — Tolerances on dimensions and mass
- GB/T 12771: Chinese National Standard for Welded Stainless Steel Tubes for General Purposes
- GB/T 14976: Chinese National Standard for Seamless Stainless Steel Tubes for Fluid Transport
Management System Certifications
- ISO 9001:2015 — Quality Management System (Quality Management System)
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health and Safety Management System
- EN 10204 / EN 10207 — Delivery Inspection Documents (Type 3.1 / Type 3.2 Certificates)
- PED (Pressure Equipment Directive 2014/68/EU) — For pressure vessel and piping applications
- NADCAP — National Aerospace and Defense Contractors Accreditation Program (for aerospace applications)
- ASME — American Society of Mechanical Engineers certification (for pressure-containing components)
Testing and Inspection Protocols
- Chemical Analysis: OES (Optical Emission Spectroscopy), wet chemical analysis for carbon and sulfur
- Mechanical Testing: Tensile testing per ASTM E8/E8M, hardness testing per ASTM E92
- Corrosion Testing: Salt spray testing (ASTM B117), intergranular corrosion testing (ASTM A262), pitting resistance testing (ASTM G48)
- Non-Destructive Testing (NDT): Eddy