Stainless Steel Coil Tube (Coiltube) — Technical Product Specification
1. Product Overview
The Stainless Steel Coil Tube (盘管, Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered coiled tube product designed for applications requiring high thermal efficiency, mechanical flexibility, and long-term corrosion resistance. Unlike straight seamless tubes, coil tubes are produced through a continuous cold-rolling and coiling process, resulting in a helical geometry that offers superior surface-area-to-volume ratios and inherent spring-back characteristics.
This product line encompasses a wide range of coil tube configurations, including external ice-melting trough coils (外融冰槽盘管), heat exchanger coils, fluid transfer coils, and process piping coils. The coiled geometry provides unique advantages in heat transfer applications, where the continuous curvature enhances turbulent flow and promotes efficient heat exchange between the tube medium and the surrounding environment.
The product catalog reference Item No. 1298 classifies this coil tube within the Coil Tube (盘管) product family, which represents a critical segment of the stainless steel tube market, particularly in thermal management, cryogenic engineering, and industrial process systems.
2. Material & Properties
2.1 Commonly Available Grades
Coil tubes are manufactured from a variety of austenitic and duplex stainless steel grades, selected based on the specific service environment:
- SUS304 / AISI 304 / 06Cr19Ni10 — General-purpose austenitic stainless steel with excellent formability and corrosion resistance in atmospheric and mild chemical environments. Chromium content: 18–20%; Nickel content: 8–10.5%.
- SUS304L / AISI 304L / 022Cr19Ni10 — Low-carbon variant (C ≤ 0.03%) designed for welded applications where sensitization resistance is critical.
- SUS316L / AISI 316L / 022Cr17Ni12Mo2 — Molybdenum-bearing grade offering superior resistance to pitting and crevice corrosion in chlorinated environments. Molybdenum content: 2.0–2.5%.
- SUS321 / AISI 321 / 06Cr18Ni11Ti — Titanium-stabilized grade suitable for elevated-temperature applications (up to 870°C) where intergranular corrosion resistance is required.
- SUS316Ti / AISI 316Ti — Titanium-stabilized variant of 316L combining high-temperature strength with molybdenum-enhanced corrosion resistance.
- Super Duplex 2205 / UNS S31803 — High-strength duplex stainless steel with PREN (Pitting Resistance Equivalent Number) ≥ 34, suitable for aggressive chloride environments and cryogenic applications.
2.2 Mechanical Properties (Typical — Annealed Condition)
| Property | SUS304 / 304L | SUS316L | Super Duplex 2205 |
|---|---|---|---|
| Tensile Strength (Rm, MPa) | ≥ 520 | ≥ 485 | ≥ 550 |
| Yield Strength (Rp0.2, MPa) | ≥ 205 | ≥ 170 | ≥ 450 |
| Elongation (A50, %) | ≥ 40 | ≥ 40 | ≥ 25 |
| Hardness (HBW, annealed) | ≤ 210 | ≤ 210 | ≤ 310 |
| Density (g/cm³) | 7.93 | 8.00 | 7.80 |
| Thermal Conductivity (W/m·K, 20°C) | 16.3 | 14.6 | 12.0 |
| Maximum Service Temperature (°C) | 870 | 870 | 300 (continuous) |
| PREN (Pitting Resistance Equivalent Number) | ≈ 19 | ≈ 24 | ≥ 34 |
2.3 Corrosion Resistance Characteristics
The passive chromium oxide film (Cr2O3) formed on the surface of stainless steel coil tubes provides a self-healing protective layer. In ice-melting and cryogenic applications, the coil tube must withstand repeated thermal cycling between sub-zero and ambient temperatures without degradation of the passive film. SUS316L and Super Duplex 2205 grades are particularly recommended for environments containing de-icing salts (NaCl, CaCl2) or road salts, where chloride-induced pitting corrosion is a primary concern.
3. Specifications
3.1 Dimensional Specifications
| Parameter | Specification Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | Φ3.0 mm – Φ50.8 mm (typical); custom sizes available | ASTM A213 / GB/T 12771 |
| Wall Thickness (WT) | 0.3 mm – 3.0 mm | ASTM A213 / GB/T 12771 |
| Coil Outer Diameter (COD) | Φ100 mm – Φ1200 mm | Manufacturer specification |
| Coil Length per Spool | Up to 200 m (continuous coil) | — |
| OD Tolerance | ±0.1 mm (precision); ±0.15 mm (standard) | ASTM A213, Table 4 |
| Wall Thickness Tolerance | ±10% (minimum); ±0.05 mm (precision) | ASTM A213 / ASME B36.19M |
| Straightness | ≤ 1.5 mm per meter (after uncoiling) | ISO 1127 |
| Surface Roughness (Ra) | ≤ 1.6 μm (standard); ≤ 0.4 μm (electropolished) | ASTM A269 / ISO 1302 |
3.2 Surface Finish Options
- 2B Annealed Finish — Standard cold-rolled and annealed surface; suitable for general industrial applications.
- No. 4 Brushed Finish — Unidirectional brushed surface with decorative appearance; suitable for architectural and visible installations.
- Electropolished Finish (EP) — Electrochemical polishing to achieve Ra ≤ 0.4 μm; essential for pharmaceutical, food-grade, and sanitary applications.
- Mirror Polish (8K) — Ra ≤ 0.1 μm; used in high-specification cosmetic and instrumentation applications.
3.3 Applicable Standards
- ASTM A213 / A213M — Standard Specification for Seamless Austenitic Stainless Steel Tubes for High-Temperature Service
- ASTM A269 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Sanitary Tubing
- ASME B36.19M — Dimensional Requirements for Stainless Steel Pipe
- GB/T 12771 — Welded Stainless Steel Tubes for Fluid Transport (Chinese National Standard)
- EN 10216-5 — European Standard for Welded Stainless Steel Tubes
- ISO 1127 — Tolerances for Straightness of Tubes
4. Manufacturing Process
4.1 Process Flow
- Raw Material Inspection — Incoming stainless steel strip or sheet undergoes chemical composition verification (spectroscopic analysis), mechanical property testing, and visual surface inspection in accordance with the specified grade standard.
- Slitting & Edge Trimming — The raw coil is slit to the target width and edge quality is verified to prevent defects during tube forming.
- Tube Forming (Roll Forming) — The flat strip is fed through a series of progressive rolls that gradually shape the material into a circular cross-section. The forming force is carefully controlled to prevent surface cracking, especially in thinner wall sections.
- Welding (for Welded Tubes) — The formed tube seam is welded using Automated TIG (Tungsten Inert Gas) Welding or Laser Welding with continuous argon (Ar) internal gas shielding to prevent oxidation at the weld root. Weld parameters are optimized to achieve full penetration with minimal heat-affected zone (HAZ).
- Coiling — The continuous tube is wound onto a coil form using a precision coiling head. The coil diameter and winding tension are controlled to ensure uniform curvature and prevent deformation. The coil is secured with banding and wrapped in protective packaging.
- Solution Annealing & Pickling — Tubes are heated to 1010–1150°C in a protective atmosphere (endothermic gas or vacuum), then rapidly quenched to restore the austenitic microstructure, dissolve carbides, and homogenize the grain structure. Subsequent acid pickling (HNO3 + HF mixture) removes surface scale and restores the passive chromium oxide film.
- Pasivation Treatment — Nitric acid or citric acid passivation is applied to enhance the chromium oxide passive layer, ensuring maximum corrosion resistance from the point of delivery.
- Final Quality Inspection — Includes dimensional measurement (OD, WT via ultrasonic or eddy current), hydrostatic testing (for pressure applications), visual weld inspection, and chemical spot verification.
4.2 Key Process Parameters
| Process Step | Key Parameter | Typical Value |
|---|---|---|
| TIG Welding | Welding Current / Shielding Gas Flow | 80–200 A / 8–12 L/min Ar |
| Laser Welding | Laser Power / Welding Speed | 3–10 kW / 3–8 m/min |
| Solution Annealing | Temperature / Dwell Time | 1050–1120°C / 2–5 min |
| Hydrostatic Testing | Test Pressure / Hold Time | 1.5× PS / ≥ 5 s |
| Coiling | Winding Tension / Layer Alignment | Controlled by servo system / ±1 mm |
5. Applications
5.1 Ice-Melting & Cryogenic Systems
Based on the referenced research study "Experimental Study on the Ice-Melting Process of Coil-Type External Ice-Melting Troughs: Heat Absorption Characteristics", coil tubes are extensively employed in external ice-melting trough systems (外融冰槽). In these systems, a circulating heat transfer fluid (typically brine solution or heated water) flows through the coiled tube array embedded in or adjacent to the trough structure. The helical geometry of the coil tube maximizes the heat transfer surface area within a compact spatial envelope, enabling efficient and uniform ice melting while minimizing thermal gradients that could cause structural cracking of the trough material.
Key design considerations for ice-melting coil tube applications include:
- Thermal cycling resistance between −30°C and +80°C without loss of mechanical integrity.
- Resistance to chloride-induced pitting from de-icing salt exposure.
- Uniform heat absorption characteristics along the coil length to prevent localized thermal stress.
- Compatibility with aggressive heat transfer fluids (glycol-based brines, CaCl2 solutions).
5.2 Other Major Application Domains
- Heat Exchangers — Coil tubes are used in shell-and-coil heat exchangers, air-to-water heat exchangers, and condensers where the coiled geometry provides high heat transfer efficiency in a compact footprint.
- Refrigeration & HVAC Systems — Evaporator and condenser coils in commercial refrigeration units, heat pumps, and air conditioning systems.
- Chemical Processing — Process piping in chemical plants where corrosion resistance and flexibility of coiled configurations are required.
- Food & Beverage Industry — Sanitary-grade tubing (316L EP finish) for fluid transfer, CIP (Clean-in-Place) systems, and brewing equipment.
- Pharmaceutical & Biotechnology — Electropolished coil tubing for bioreactors, purification systems, and sterile fluid handling.
- Automotive & Aerospace — Fuel lines, hydraulic lines, and exhaust components utilizing the flexibility and corrosion resistance of stainless steel coil tubes.
- Oil & Gas — Downhole tubing, subsea umbilicals, and process piping in offshore platforms.
- Structural & Architectural — Decorative railings, handrails, and structural framing in coastal or high-corrosion environments.
6. Quality Certifications & Testing
6.1 Factory Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains the following quality and management system certifications:
- ISO 9001:2015 — Quality Management System
- ISO 14001 — Environmental Management System
- ISO 45001 — Occupational Health and Safety Management System
- CE Marking — Conformity with European standards for product safety
- PED (Pressure Equipment Directive 2014/68/EU) — For pressure-containing tube applications