Stainless Steel Coil Tube — Industrial Coiltube Product Series
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a continuous-length tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd, designed for demanding industrial applications requiring high corrosion resistance, mechanical integrity, and flexibility in processing. Unlike conventional straight-length seamless or welded pipes, coil tubes are produced in continuous rolled forms, enabling downstream users to cut to precise lengths on demand, thereby minimizing material waste and optimizing production efficiency.
Coil tubes find extensive use in fluid conveying systems, structural components, heat exchangers, chemical processing equipment, and specialized material handling systems such as disc pipeline scraper conveyors — where discrete element method (DEM) simulation and multi-attribute evaluation studies have demonstrated the critical role of tubing geometry, surface finish, and material properties in conveying performance and system reliability.
2. Material & Properties
2.1 Common Grades
- 304 (UNS S30400) — Austenitic stainless steel with excellent general corrosion resistance and formability. The most widely specified grade for industrial coil tubes.
- 316 (UNS S31600) — Molybdenum-enhanced austenitic stainless steel offering superior resistance to pitting and crevice corrosion in chloride environments.
- 321 (UNS S32100) — Titanium-stabilized austenitic grade providing enhanced resistance to intergranular corrosion at elevated temperatures (up to 870 °C).
- 310S (UNS S31008) — High-temperature austenitic grade suitable for service temperatures exceeding 1100 °C.
- 430 (UNS S43000) — Ferritic stainless steel offering moderate corrosion resistance at a reduced cost; magnetic and non-hardenable by heat treatment.
- 316L (UNS S31603) — Low-carbon variant of 316, preferred for welding applications where sensitization resistance is critical.
2.2 Key Material Properties
| Property | 304 / 304L | 316 / 316L | 321 | 430 |
|---|---|---|---|---|
| Carbon (C), max % | 0.08 / 0.03 | 0.08 / 0.03 | 0.08 | 0.12 |
| Chromium (Cr), % | 18.0–20.0 | 16.0–18.0 | 18.0–20.0 | 16.0–18.0 |
| Nickel (Ni), % | 8.0–10.5 | 10.0–14.0 | 9.0–12.0 | — |
| Molybdenum (Mo), % | — | 2.0–3.0 | — | — |
| Tensile Strength (UTS), min MPa | 515 | 515 | 515 | 450 |
| Yield Strength (0.2% RP), min MPa | 205 | 205 | 205 | 205 |
| Elongation (%), min | 40 | 40 | 40 | 25 |
| Density, g/cm³ | 8.00 | 8.03 | 8.00 | 7.70 |
| Thermal Conductivity (20 °C), W/m·K | 16.3 | 16.3 | 16.3 | 26.1 |
| Magnetic Susceptibility | Non-magnetic (austenitic) | Non-magnetic (austenitic) | Non-magnetic (austenitic) | Magnetic (ferritic) |
2.3 Microstructural Characteristics
Austenitic grades (304, 316, 321) exhibit a face-centered cubic (FCC) crystal structure, which confers excellent ductility, formability, and resistance to stress corrosion cracking (SCC) in non-chloride environments. The addition of molybdenum in 316 enhances passive film stability, while titanium stabilization in 321 prevents chromium carbide precipitation at grain boundaries during welding or heat exposure — a phenomenon known as sensitization.
3. Specifications
| Parameter | Specification Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 159.0 mm | ASTM A554 / ASTM A555 |
| Wall Thickness | 0.5 mm – 6.0 mm | ASTM A554 / EN 10217 |
| OD Tolerance | ±0.10 mm – ±0.30 mm (depending on size) | ASTM A554 |
| Wall Thickness Tolerance | ±10% (standard); ±5% (close tolerance available) | ASTM A554 |
| Surface Finish | 2B, No.1 Annealed & Pickled, BA (Bright Annealed), Custom polished | ASTM A480 |
| Hardness (Rockwell B) | 80 – 100 HRB (annealed condition) | ASTM A554 |
| Coil Length | Up to 100 m continuous (custom lengths available) | Manufacturer specification |
| Coil Weight | Up to 5,000 kg per coil | Manufacturer specification |
| Manufacturing Method | ERW (Electric Resistance Welded) / Seamless (perforated-rolled) | ASTM A554 / ASTM A555 |
| Heat Treatment | Annealed and Pickled (A&P) | ASTM A480 |
| End Condition | Plain, beveled, or flanged (upon request) | — |
4. Manufacturing Process
4.1 Raw Material Preparation
Hot-rolled stainless steel strip or coil is supplied from certified mills and undergoes incoming inspection for chemical composition (via optical emission spectrometry, OES) and mechanical properties. The strip is slitted to the required width with precise edge quality to ensure uniform weld formation during the tube-rolling stage.
4.2 Tube Forming
- Coiling & Feeding: The flat strip is loaded onto a pay-off reel and fed through a series of progressively closing roll forming stations (typically 8–12 stations) to gradually bend the flat profile into a tubular shape with a longitudinal seam.
- Seam Welding (ERW Process): The formed strip passes through high-frequency electric resistance welding (HF-ERW) equipment, where an electromagnetic field generates localized resistance heating at the seam edges, achieving full penetration welds at temperatures exceeding 1,200 °C without external filler material. This ensures metallurgical continuity and mechanical strength equivalent to the parent material.
- Internal & External Finishing: The weld seam is finished by internal welding rollers and external grinding/brushing to achieve a smooth surface and consistent wall thickness.
4.3 Heat Treatment
The welded coil tube is subjected to annealing and pickling (A&P) in a continuous annealing furnace at 1,050–1,150 °C under a controlled reducing atmosphere (typically endothermic gas or hydrogen mixtures) to:
- Relieve residual stresses induced during cold forming and welding
- Restore full austenitic microstructure and mechanical properties
- Eliminate the weld-affected zone (WAZ) hardness gradient
- Remove oxide scales via subsequent acid pickling (HNO₃/HF blend) and passivation
4.4 Dimensional Control & Inspection
Post-heat-treatment, the coil tube passes through a sizing and straightening section to achieve final dimensional tolerances. Laser diameter gauges, ultrasonic wall thickness scanners, and automated visual inspection systems verify compliance with ASTM A554 requirements throughout the production run.
4.5 Coiling & Packaging
The finished product is coiled onto a steel core (typically 6" or 8" ID) with protective end caps. Each coil is wrapped in waterproof polyethylene film and secured with steel strapping. Desiccant bags are included to prevent moisture ingress during storage and transportation. Shipping marks include grade, dimensions, heat number, and certificate reference.
5. Applications
5.1 Fluid Conveying & Piping Systems
Coil tubes are extensively used in hygienic process piping for food and beverage processing, pharmaceutical manufacturing, and dairy industries, where the continuous coil format allows for custom-length fabrication and sanitary welding. The smooth internal surface (achievable with BA finish, Ra ≤ 0.4 μm) minimizes bacterial adhesion and facilitates Clean-in-Place (CIP) procedures.
5.2 Heat Exchangers & Boiler Tubes
Grades 321 and 310S are preferred for high-temperature heat exchanger applications where thermal cycling and oxidative environments demand exceptional scale resistance. Coil format enables efficient coil winding for shell-and-coil heat exchangers.
5.3 Material Handling — Disc Pipeline Scraper Conveyors
In bulk material handling systems, stainless steel coil tubes serve as the conduit for disc pipeline scraper conveyors. Research employing Discrete Element Method (DEM) simulation and multi-attribute evaluation has demonstrated that:
- Internal surface roughness directly influences frictional drag and conveying capacity
- Wall thickness and tube diameter ratio affect scraper stability and material flow regime
- Material hardness and wear resistance determine service life under abrasive conditions
- Optimal coil tube specifications can improve conveying efficiency by up to 15–20% compared to suboptimally specified alternatives
5.4 Structural & Architectural Applications
Decorative and structural coil tubes are used in handrails, balustrades, furniture frames, and architectural cladding, where aesthetic surface finishes (mirror polish, hairline finish) and dimensional precision are paramount.
5.5 Chemical & Petrochemical Industry
316L coil tubes resist aggressive chemical media including sulfuric acid, hydrochloric acid (dilute), and seawater, making them suitable for chemical processing vessels, heat exchangers, and waste treatment systems.
6. Quality Certifications & Standards Compliance
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification ensuring consistent product quality and process control |
| ISO 14001:2015 | Environmental Management System certification for sustainable manufacturing practices |
| ASTM A554 | Standard Specification for Seamless and Welded Austenitic Stainless Steel Tube for Boiler, Heat Exchanger, and Similar Heat-Transfer Applications |
| ASTM A555 | Standard Specification for Seamless and Welded Austenitic Stainless Steel Shapes for Chemical and Similar Service |
| ASTM A480 | Standard Specification for Chemical Composition and Product Requirements for Stainless Steel Plate, Sheet, and Strip |
| EN 10217-7 | European standard for non-alloy and alloy steel tubes for pressure purposes — austenitic stainless steel tubes |
| GB/T 14976 | Chinese National Standard for stainless steel seamless tubes for fluid conveyance |
| 3.1 Certification (EN 10204) | Third-party inspection certificate providing full chemical and mechanical test data for each heat |
| MTC (Mill Test Certificate) | Full material traceability documentation including chemical analysis, mechanical test results, and heat treatment records |