Stainless Steel Coil Tube (Coiltube) — Thin-Wall Seamless Internal Threaded Specification
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd represents a high-precision, thin-wall seamless coil tube product engineered for demanding industrial applications requiring superior corrosion resistance, mechanical integrity, and dimensional accuracy. This product line draws upon advanced metallurgical research and production methodologies originally developed for thin-wall internal threaded seamless tubing, adapted here for stainless steel alloy systems to deliver exceptional performance in fluid transport, heat exchange, and structural applications.
The coil tube format provides significant advantages in material utilization efficiency, continuity of supply, and downstream processing convenience compared to straight-length tubing. Each coil is wound with precise tension control to ensure uniform mechanical properties throughout the length and to prevent permanent deformation or work-hardening during the coiling process.
Material & Properties
Base Alloy Grades
- AISI 304 / UNS S30400 — General-purpose austenitic stainless steel offering excellent corrosion resistance in oxidizing environments, food-grade compatibility, and good formability.
- AISI 304L / UNS S30403 — Low-carbon variant of 304 suitable for welding applications where sensitization resistance is critical.
- AISI 316 / UNS S31600 — Molybdenum-enhanced austenitic grade providing superior resistance to pitting and crevice corrosion in chloride-containing environments.
- AISI 316L / UNS S31603 — Low-carbon 316 variant optimized for weldability and resistance to intergranular corrosion.
- AISI 321 / UNS S32100 — Titanium-stabilized grade offering enhanced resistance to intergranular corrosion at elevated temperatures (up to 870°C / 1600°F).
- AISI 310S / UNS S31008 — High-temperature austenitic grade suitable for continuous service up to 1150°C (2100°F).
Mechanical Properties (Typical, Annealed Condition)
| Property | 304 / 304L | 316 / 316L | 321 | 310S |
|---|---|---|---|---|
| Tensile Strength (Minimum), MPa | 515 | 515 | 515 | 515 |
| Yield Strength (0.2% offset), MPa | 205 | 205 | 205 | 205 |
| Elongation (in 50 mm / 2 in), % | ≥40 | ≥40 | ≥40 | ≥40 |
| Density, g/cm³ | 8.0 | 8.0 | 8.0 | 8.0 |
| Thermal Conductivity (100°C), W/(m·K) | 16.3 | 16.3 | 16.3 | 18.5 |
| Modulus of Elasticity, GPa | 193 | 193 | 193 | 200 |
Corrosion Resistance Characteristics
- Pitting Resistance Number (PREN): 304 ≈ 18–20; 316 ≈ 24–26; 316L ≈ 24–26; 321 ≈ 18–20; 310S ≈ 19–21
- Maximum Service Temperature (oxidizing atmosphere): 304/316/321 — 870°C (1600°F); 310S — 1150°C (2100°F)
- Maximum Service Temperature (reducing atmosphere): 304/316 — 593°C (1100°F); 321 — 870°C (1600°F); 310S — 1093°C (2000°F)
Specifications
| Parameter | Specification / Range |
|---|---|
| Outer Diameter (OD) | 3.0 mm – 50.8 mm (1/8" – 2") |
| Wall Thickness (WT) | 0.3 mm – 2.0 mm (0.012" – 0.079") |
| Coil Inner Diameter (ID) | 200 mm – 600 mm (8" – 24") |
| Coil Length per Roll | 50 m – 300 m (164 ft – 984 ft) |
| Coil Weight per Roll | 50 kg – 500 kg (110 lb – 1,100 lb) |
| Surface Finish | 2B (Cold Rolled + Annealed + Pickled), BA (Bright Annealed), No. 4 Brushed, Mirror (8K), Custom |
| Tolerance — OD | ±0.05 mm (0.002") to ±0.10 mm (0.004") per ASTM A511 |
| Tolerance — Wall Thickness | ±10% of nominal |
| Straitness (per 300 mm) | ≤1.0 mm |
| Winding Quality | Tight, uniform layers; no inter-layer damage; edge alignment within 3 mm |
| Applicable Standards | ASTM A511, ASTM A213, EN 10217-7, EN 10216-5, GB/T 12771, GB/T 14976 |
| Delivery Condition | Annealed (A), Cold Worked (CW), Solution Annealed (SA), Pickled & Passivated (P&P) |
| Packaging | Wooden pallet + waterproof wrapping; or export-standard steel frame with moisture-absorbing desiccant |
Manufacturing Process
The production of high-quality thin-wall stainless steel coil tubes follows a rigorous multi-stage manufacturing sequence, integrating advanced metallurgical principles with precision mechanical engineering:
- Raw Material Selection & Inspection — Virgin stainless steel billets or slabs are sourced from certified primary mills (e.g., Outokumpu, POSCO, Tsingshan). Incoming materials undergo spectrographic analysis (OES) to verify chemical composition within ASTM/EN specification limits. Mechanical property verification is performed on sample coupons.
- Hot Rolling & Annealing — The billet is reheated to 1100–1200°C and hot-rolled into an intermediate blank. The hot-rolled product is subsequently annealed to relieve residual stresses and establish a uniform recrystallized grain structure.
- Pickling & Descaling — The hot-rolled blank is subjected to acid pickling (typically HNO₃/HF mixture or citric acid solution) to remove oxide scale, followed by passivation to establish a protective chromium oxide film on the surface.
- Cold Drawing & Piercing (Seamless Tube Formation) — The blank is cold-drawn through precision-die tooling to achieve the desired OD and wall thickness. For seamless tube production, a piercing plug is used to create the hollow interior without any weld seam, ensuring full 360° metallurgical continuity. This process is critical for achieving the thin-wall dimensions specified.
- Cold Reduction & Sizing — Successive cold-drawing passes through calibrated die sets progressively reduce the tube dimensions while maintaining dimensional tolerances. Each pass introduces controlled cold work (typically 20–40% reduction) to develop desired mechanical strength without compromising ductility.
- Intermediate Annealing — At predetermined cold work levels, the tube is annealed at 1050–1100°C followed by controlled cooling (air or water quench depending on grade) to restore ductility, relieve accumulated cold-work stresses, and refine grain structure. This prevents cracking during subsequent forming operations.
- Internal Threading (Optional) — For applications requiring internal threading, precision thread-rolling or thread-cutting operations are performed on the tube interior using specialized mandrel-driven tooling. Thread profiles conform to ISO metric (M), BSP (G), or NPT standards. This operation requires extreme care to avoid distorting the thin wall geometry.
- Final Annealing & Passivation — A final solution annealing cycle ensures the tube achieves its target mechanical properties and corrosion resistance. The surface is passivated using citric acid or nitric acid solutions to maximize the passive chromium oxide layer.
- Coiling Operation — The straight tube is fed through a precision coiling station where it is wound onto a mandrel with controlled tension (typically 0.5–2.0 kN depending on tube size). The coiling speed and tension are dynamically adjusted to prevent ovality, kinking, or inter-layer contact damage. The resulting coil exhibits uniform layer-to-layer alignment and consistent mechanical properties throughout its length.
- Final Inspection & Testing — Each coil undergoes comprehensive quality verification including: dimensional measurement (OD, WT, straightness), hydrostatic pressure testing (per ASTM A511), surface finish inspection, chemical composition re-verification, and mechanical property testing on sample specimens. Non-destructive testing (eddy current or ultrasonic) may be applied for wall thickness uniformity verification.
Applications
- Automotive & HVAC Systems — Refrigerant tubing, fuel lines, and condenser/evaporator coils requiring high thermal conductivity and leak-free performance under cyclic pressure loading.
- Food & Beverage Processing — Hygienic fluid transfer lines, CIP (Clean-in-Place) compatible tubing for dairy, brewing, and pharmaceutical processing where sanitary-grade surface finish and corrosion resistance are mandatory.
- Chemical & Petrochemical Industry — Process piping for aggressive chemical environments, heat exchanger tubes, and instrumentation tubing in plants handling acids, alkalis, and chlorinated solutions.
- Medical & Laboratory Equipment — Autoclavable tubing for medical devices, fluid delivery systems in diagnostic equipment, and sterilizable components requiring biocompatibility.
- Oil & Gas Downhole Tools — Instrumentation tubing, chemical injection lines, and sensor housings operating in high-temperature, high-pressure (HTHP) subsea environments.
- Electronics & Semiconductor Manufacturing — Ultra-pure gas delivery tubing, vacuum system components, and process gas lines requiring extremely low particulate generation.
- Architectural & Decorative Applications — Custom-formed structural and aesthetic elements leveraging the coil format for efficient fabrication of complex geometries.
- Power Generation — Condenser tubes, feedwater lines, and superheater elements in thermal and nuclear power plants.
Quality Certifications & Compliance
| Certification / Standard | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System certification covering all manufacturing processes |
| ISO 14001:2015 | Environmental Management System ensuring sustainable production practices |
| ISO/TS 22163 | Automotive-specific quality management system for IATF-aligned processes |
| EN 10204 3.1 | Inspection Certificate — material certification with test reports per European standards |
| EN 10204 3.2 | Independent Third-Party Inspection Certificate for critical applications |
| NACE MR0175 / ISO 15156 | Materials for use in H₂S-containing environments in oil and gas production |
| NSF/ANSI 61 | Drinking water system components — health effects certification |
| 3-A Sanitary Standards | Dairy and food processing equipment compliance |
| PED 2014/68/EU | Pressure Equipment Directive compliance for EU market access |
Unique Selling Points
- Seamless Construction: The absence of a weld seam eliminates the primary failure point inherent in welded tubing, providing uniform 360° mechanical and corrosion resistance — critical for thin-wall applications where wall thinning at the weld could compromise integrity.
- Thin-Wall Precision: Capable of producing wall thicknesses as low as 0.3 mm with ±10% tolerance, enabling lightweight designs without sacrificing pressure containment capability.
- Coil Format Efficiency: Continuous coil supply eliminates butt-weld joints between straight lengths, reducing potential leak points by up to 95% compared to straight tube assembly, while minimizing material waste during downstream fabrication.
- Optional Internal Threading: The ability to incorporate precision internal threads directly into the coil tube enables rapid assembly without secondary machining, reducing production time and cost in applications requiring threaded connections within confined spaces.
- Multi-Grade Flexibility: Production capability across the full austenitic stainless steel range (304 through 310S) allows customers to select the optimal grade for their specific corrosion, temperature, and mechanical requirements.
- Full Traceability: Every coil is accompanied by comprehensive mill test certificates with lot-by-lot chemical analysis, mechanical test results, and heat number traceability back to the primary steel mill.
- Custom Surface Finishes: From matte 2B finish for general industrial use to mirror 8K polish for pharmaceutical and food-grade applications, surface treatment is tailored to the customer's functional and aesthetic requirements.
Note: All specifications described herein are representative values based on standard production parameters. Custom specifications, including non-standard dimensions, surface finishes, and mechanical property requirements, are available upon request subject to engineering review and minimum order quantity (MOQ) assessment. Wenzhou Jixing Metal Materials Co., Ltd maintains a dedicated technical engineering team to support customers in product selection, application engineering, and specification development.