Stainless Steel Coil Tube (Coiltube) — Product No. 663
1. Product Overview
The Stainless Steel Coil Tube (Coiltube), designated as Product No. 663 by Wenzhou Jixing Metal Materials Co., Ltd., is a precision-engineered continuous-length tubular product supplied in coiled form for downstream processing, fabrication, and installation. Unlike traditional cut-length seamless or welded pipes, coil tubes are manufactured in a continuous winding format, offering superior material utilization, reduced cutting waste, and enhanced production efficiency for high-volume industrial and commercial applications.
Coil tubes are particularly advantageous for applications requiring long, uninterrupted runs of piping — such as building water distribution systems, industrial process lines, HVAC networks, and solar thermal collector systems. The coiled configuration allows for rapid deployment and minimizes joint density, thereby reducing potential leakage points and improving system integrity over the operational lifespan.
2. Material & Properties
2.1 Base Material Grades
The coil tube is manufactured from austenitic stainless steel grades conforming to international standards. The primary grades offered include:
- 304 (UNS S30408 / 1.4301) — General-purpose grade with excellent corrosion resistance, formability, and weldability. Suitable for potable water, food-grade, and chemical processing applications.
- 304L (UNS S30403 / 1.4307) — Low-carbon variant of 304, designed to resist intergranular corrosion during welding and high-temperature service.
- 316 (UNS S31608 / 1.4401) — Molybdenum-enhanced grade offering superior resistance to pitting and crevice corrosion in chloride-containing environments.
- 316L (UNS S31603 / 1.4404) — Low-carbon version of 316, recommended for welded assemblies and aggressive chemical media.
- 321 (UNS S32108 / 1.4541) — Titanium-stabilized grade with enhanced resistance to intergranular corrosion at elevated temperatures (450–850°C).
- 310S (UNS S31008 / 1.4845) — High-temperature grade with outstanding oxidation resistance, suitable for furnace and heat exchanger applications.
2.2 Chemical Composition (Typical, wt%)
| Grade | C (Max) | Mn (Max) | P (Max) | S (Max) | Silicon (Max) | Cr | Ni | Mo | Ti |
|---|---|---|---|---|---|---|---|---|---|
| 304 | 0.08 | 2.00 | 0.045 | 0.030 | 1.00 | 18.0–20.0 | 8.0–10.5 | — | — |
| 304L | 0.03 | 2.00 | 0.045 | 0.030 | 1.00 | 18.0–20.0 | 8.0–12.0 | — | — |
| 316 | 0.08 | 2.00 | 0.045 | 0.030 | 1.00 | 16.0–18.0 | 10.0–14.0 | 2.0–3.0 | — |
| 316L | 0.03 | 2.00 | 0.045 | 0.030 | 1.00 | 16.0–18.0 | 10.0–14.0 | 2.0–3.0 | — |
| 321 | 0.08 | 2.00 | 0.045 | 0.030 | 1.00 | 17.0–19.0 | 9.0–12.0 | — | 0.40–0.70 |
2.3 Mechanical Properties (Annealed Condition)
| Property | 304 / 304L | 316 / 316L | 321 |
|---|---|---|---|
| Tensile Strength (Rm) | ≥ 520 MPa | ≥ 520 MPa | ≥ 520 MPa |
| 0.2% Proof Stress (Rp0.2) | ≥ 205 MPa | ≥ 170 MPa | ≥ 205 MPa |
| Elongation (A50) | ≥ 35% | ≥ 35% | ≥ 35% |
| Hardness (HV) | ≤ 200 | ≤ 210 | ≤ 200 |
2.4 Surface Finishes
- 2B Finish — Cold-rolled, annealed, and pickled; smooth, matte appearance. Suitable for general industrial and structural applications.
- No. 4 Brushed Finish — Directional grain pattern; commonly used in architectural and food processing applications.
- Mirror Finish (8K) — Polished to a reflective surface; used in decorative, medical, and pharmaceutical applications.
- Pickled & Passivated (Pickled & Passivated, P&P) — Chemically cleaned and passivated to enhance corrosion resistance; standard for sanitary and food-grade systems.
- E.P. (Electro-Polished) — Electrolytically polished to achieve ultra-smooth surface (Ra ≤ 0.4 μm); required for pharmaceutical, biotech, and CIP (Clean-in-Place) systems.
3. Specifications
| Parameter | Specification |
|---|---|
| Product Type | Stainless Steel Coil Tube (Continuous Coiled Tubing) |
| Product No. | 663 |
| Manufacturing Method | Seamless (Cold Drawing / Cold Rolling) or ERW (Electric Resistance Welded) |
| Outer Diameter (OD) | Φ3 mm – Φ219 mm (custom sizes available upon request) |
| Wall Thickness (WT) | 0.3 mm – 12 mm |
| Coil Length | 5 m – 200 m per coil (customizable) |
| Coil Inner Diameter (CID) | Φ500 mm – Φ1,200 mm |
| Coil Outer Diameter (COD) | Φ1,000 mm – Φ2,000 mm |
| Tolerance — OD | ±0.1 mm (OD ≤ 50 mm); ±0.5% (OD > 50 mm) |
| Tolerance — Wall Thickness | ±10% (WT ≤ 3 mm); ±10% (WT > 3 mm) |
| Roundness | ≤ 0.5% of OD |
| Straightness | ≤ 1.5 mm/m (for uncoiled sections) |
| Standards Complied | ASTM A269 / A270, ASTM A554, EN 10217-7, EN 10216-5, GB/T 14976, GB/T 13296 |
| Available Grades | 304, 304L, 316, 316L, 321, 310S, 2205 (Duplex), 904L |
| Surface Treatment | 2B, No. 4, Mirror (8K), Pickled & Passivated, E.P. |
| End Condition | Plain, Beveled, Threaded, Flanged, or Custom Fitting |
| Testing | Hydrostatic Pressure Test, Eddy Current (EC) Testing, Visual Inspection |
| Packaging | Wooden crate / Export-grade packaging with moisture-proof wrapping |
| Minimum Order Quantity | 1 coil (negotiable based on grade and specification) |
4. Manufacturing Process
The production of stainless steel coil tubes follows a rigorous multi-stage process to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Procurement & Inspection — High-quality stainless steel slabs or billets are sourced from certified mills. Incoming materials undergo spectrographic analysis (OES — Optical Emission Spectroscopy) to verify chemical composition compliance.
- Hot Rolling — The steel slab is heated to 1,100–1,200°C and hot-rolled into a seamless tube blank or a flat strip (for ERW processes). Hot rolling establishes the initial dimensions and homogenizes the microstructure.
- Pickling & Decapping — The hot-rolled product is acid-pickled (using a mixture of hydrochloric and nitric acid) to remove the iron oxide scale formed during hot rolling, revealing a clean metallic surface.
- Cold Drawing / Cold Rolling — The tube blank is cold-drawn through precision-die tooling to achieve the final outer diameter and wall thickness. Cold working introduces beneficial residual compressive stresses that enhance fatigue resistance and improves surface finish. For ERW processes, the flat strip is cold-rolled into a C-shaped profile before welding.
- Welding (ERW Process Only) — For welded coil tubes, the C-shaped strip is formed into a tube and welded using Electric Resistance Welding (ERW) technology. The weld seam is subsequently subjected to inline inspection via eddy current testing (ECI) to detect any subsurface discontinuities.
- Heat Treatment (Annealing) — The cold-worked tube is solution-annealed at 1,050–1,100°C followed by rapid quenching (air or water cooling) to fully austenitize the microstructure, relieve residual stresses, and restore ductility. For stabilized grades (e.g., 321), a stabilization heat treatment at 870–900°C may be applied to precipitate titanium carbides.
- Pickling & Passivation — Post-annealing pickling removes any oxide scale, followed by passivation using nitric acid or citric acid to enrich the surface chromium oxide layer, enhancing passive film stability and corrosion resistance.
- Coiling — The continuous tube is wound onto a coil mandrel using a precision coiling machine with tension control to ensure uniform coil geometry, minimal distortion, and consistent inter-layer stacking.
- Final Inspection & Testing — Each coil undergoes comprehensive quality assurance including:
- Dimensional verification (OD, wall thickness, straightness)
- Hydrostatic pressure testing (typically 1.5–2.0× working pressure)
- Eddy current (EC) inline inspection for wall thickness uniformity and seam integrity
- Visual surface inspection for defects, scratches, or discoloration
- Chemical composition verification via OES or ICP-OES
- Mechanical property testing (tensile, hardness) per lot
- Packaging & Dispatch — Coils are wrapped in moisture-proof plastic film, secured with steel strapping, and packed in export-grade wooden crates or placed on skid pallets for sea or land transport.
5. Applications
The versatility of stainless steel coil tubes extends across a wide range of industries and applications:
5.1 Building Water Distribution Systems
Coil tubes are extensively used in residential, commercial, and institutional building water supply networks. Their hygienic surface finish, resistance to biofilm formation, and long service life make them ideal for potable water distribution. The continuous coil format allows for rapid installation with minimal joints, significantly reducing the risk of water leakage and contamination — a critical consideration in the context of building pipe network rectification and compliance with public health standards.
5.2 Industrial Process Piping
- Chemical processing plants — acid, alkali, and solvent transfer lines
- Petrochemical facilities — refinery process piping and heat exchanger tubes
- Pharmaceutical manufacturing — CIP-compatible process lines and sanitary piping
- Food and beverage processing — milk, juice, and beverage transfer systems
- Power generation — boiler feedwater lines, condensate return systems
5.3 HVAC & Refrigeration
Coil tubes serve as the core component in air conditioning and refrigeration systems, including evaporator and condenser coils. The high thermal conductivity and corrosion resistance of austenitic stainless steel ensure efficient heat transfer and long-term durability in humid, condensing environments.
5.4 Solar Thermal Systems
Stainless steel coil tubes are employed as heat collector tubes in solar thermal energy systems, including evacuated tube collectors and flat-plate collectors. The material's thermal stability and resistance to thermal cycling make it suitable for repeated heating and cooling cycles.
5.5 Architectural & Decorative Applications
Mirror-finish and brushed-finish coil tubes are used in architectural features such as handrails, balustrades, decorative facades, and interior design elements, combining structural integrity with aesthetic appeal