Stainless Steel Coil Tube (Coiltube) — Product Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (catalog reference: No. 1633) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a continuous-length tubular product wound into a helical coil configuration, designed for downstream forming, bending, and fabrication operations. Unlike seamless or welded pipe delivered in straight lengths, coil tube is supplied in a coiled state from the production line, offering significant advantages in material utilization, logistics efficiency, and processing flexibility.
Coil tube represents a critical intermediate form in the stainless steel tube value chain. It bridges the gap between raw tube mill output and finished pipe products, serving as the feedstock for secondary processes such as cold drawing, expanding, bending, and coiling/uncoiling into finished lengths. The coil tube machine (盘管机, Coil Tube Winding Machine) is the specialized equipment responsible for winding continuous tube output from the forming line into organized coils for storage and transport.
Definition: A coil tube is a continuous length of stainless steel tube, produced by a cold-rolled or hot-rolled tube mill, that is wound into a helical coil (typically using a coil tube machine) immediately after the welding and cutting-off stages, to facilitate handling, transportation, and subsequent processing.
2. Material & Properties
2.1 Common Alloy Grades
Coil tubes are manufactured from a wide range of austenitic, ferritic, and duplex stainless steel grades, selected according to the end-application requirements:
- ASTM A213 TP304 / 304L — General-purpose austenitic grade with excellent corrosion resistance and formability
- ASTM A213 TP316 / 316L — Molybdenum-bearing austenitic grade with superior resistance to pitting and crevice corrosion
- ASTM A213 TP321 — Stabilized austenitic grade (Ti-stabilized) for high-temperature applications
- ASTM A213 TP347 — Niobium-stabilized austenitic grade for elevated temperature service
- ASTM A312 TP410 / 430 — Ferritic grades for cost-sensitive, moderate corrosion environments
- ASTM A790 S31803 / S32205 — Duplex stainless steel grades for high-strength, high-corrosion-resistance applications
2.2 Mechanical Properties (Typical — Solution Annealed Condition)
| Property | 304 / 304L | 316 / 316L | 321 | S31803 (Duplex) |
|---|---|---|---|---|
| Tensile Strength (MPa) | ≥ 515 | ≥ 515 | ≥ 515 | ≥ 795 |
| Yield Strength (MPa) | ≥ 205 | ≥ 205 | ≥ 205 | ≥ 450 |
| Elongation (%) | ≥ 40 | ≥ 40 | ≥ 40 | ≥ 15 |
| Hardness (HB) | ≤ 217 | ≤ 217 | ≤ 217 | ≤ 350 |
| Density (g/cm³) | 8.00 | 8.00 | 8.00 | 7.80 |
| Thermal Conductivity (W/m·K, 100°C) | 16.3 | 16.3 | 16.3 | 11.6 |
| Modulus of Elasticity (GPa) | 193 | 193 | 193 | 200 |
2.3 Surface Finish Options
- 2B Finish — Cold-rolled, annealed, and bright-passed; standard commercial finish
- No. 4 Brushed Finish — Uniformly brushed with visible grain lines
- No. 8 Mirror Finish — Highly polished, reflective surface (Ra ≤ 0.25 μm)
- Pickled & Passivated (P&P) — Acid-pickled to remove scale, followed by passivation treatment
- Electropolished — Electrochemical polishing for ultra-smooth, sanitary-grade surface
3. Specifications
| Parameter | Specification |
|---|---|
| Outer Diameter (OD) | 3.00 mm – 168.00 mm (custom sizes available upon request) |
| Wall Thickness (WT) | 0.20 mm – 6.00 mm |
| Coil Length | Typically 50 m – 200 m per coil (configurable) |
| Coil Weight | 500 kg – 3,000 kg per coil (standard range) |
| OD Tolerance | ±0.05 mm (precision) to ±0.50 mm (standard) |
| WT Tolerance | ±10% (standard) to ±5% (precision) |
| Roundness | ≤ 0.5% of OD |
| End Condition | Beveled, plain cut, or customized per drawing |
| Weld Type | Continuous welded (ERW / PGW / TIG) or seamless (for specific grades) |
| Applicable Standards | ASTM A213, ASTM A312, ASME SA-213, ASME SA-312, EN 10216-5, GB/T 12771 |
| Packaging | Export-grade wooden pallets with moisture-proof wrapping; protective end caps |
4. Manufacturing Process
4.1 Overview of the Coil Tube Production Flow
The production of stainless steel coil tube involves a series of precisely controlled metallurgical and mechanical operations. The following describes the complete process flow from raw material to finished coil:
- Raw Material Preparation: Cold-rolled stainless steel strip (or hot-rolled coil) is supplied in strip form, typically 0.2–6.0 mm in thickness, from reputable mill sources. Incoming material undergoes strict chemical composition verification via OES (Optical Emission Spectroscopy) and physical inspection.
- Strip Uncoiling & Leveling: The strip is uncoiled from the raw material coil and passed through a leveling unit to eliminate residual stresses and ensure flatness within acceptable tolerances.
- Slitting (if required): Wide-strip material may be slit to the required width for the target tube outer diameter.
- Forming (Rolling): The flat strip is passed through a series of progressively closing rolls (forming stands) that incrementally deform the strip into a near-circular cross-section. The number of forming stands (typically 12–25) depends on the OD-to-WT ratio and material grade.
- Welding: The formed tube is longitudinally welded using one of the following methods:
- PGW (Plasma Gas Welding): Uses a plasma arc to create a molten pool; suitable for general-purpose applications.
- ERW (Electric Resistance Welding): Induction heating melts the weld seam; higher production speed.
- TIG (Tungsten Inert Gas Welding): Argon-shielded arc welding; highest quality weld seam, used for sanitary and high-purity applications.
- Weld Heat Treatment: The welded tube passes through a furnace for weld annealing (typically at 1050–1150°C for austenitic grades), which relieves welding residual stresses, restores corrosion resistance at the weld zone, and achieves the desired grain structure.
- Cooling & Pickling: The annealed tube is cooled (air or water quench depending on grade) and then pickled in a mixed acid bath (HNO₃ + H₂SO₄ or HNO₃ + HF) to remove oxide scale and restore the passive chromium oxide layer.
- Passivation: A controlled nitric acid or citric acid passivation treatment is applied to ensure a uniform, stable passive film on the tube surface.
- Coil Winding (盘管机 — Coil Tube Machine Operation): The continuous tube is wound onto a coil tube machine (盘管机). This is a critical operation requiring precise control of:
- Tension control to prevent tube deformation or kinking
- Layer stacking accuracy to ensure uniform coil geometry
- Winding speed synchronization with upstream production speed
- End-of-coil detection and automatic cut-off
- Quality Inspection & Testing: Each coil undergoes comprehensive quality verification (see Section 6).
- Marking, Packaging & Storage: Coils are marked with grade, heat number, dimensions, and lot identification. They are then packaged in export-grade protection and stored in a dry, controlled environment.
4.2 The Coil Tube Machine (盘管机) — Technical Notes
The Coil Tube Machine (盘管机) is the specialized winding equipment that transforms continuous tube output into organized coils. Key technical considerations in coil tube machine operation include:
- Tension Control System: Maintains constant winding tension (typically 200–800 N depending on OD and WT) to prevent inter-layer slippage and maintain coil integrity.
- Pay-Off / Pay-In Geometry: The winding pattern (spiral, helical, or layered) must be optimized to minimize tube ovality and surface damage.
- Speed Matching: The winding speed must dynamically match the production line speed to prevent tension spikes or slack.
- Coil Diameter Control: Automatic diameter measurement ensures the coil meets dimensional specifications for downstream equipment compatibility.
- End Preparation: The machine controls the final tube length, ensuring consistent coil lengths and minimal off-cut waste.
5. Applications
Stainless steel coil tube finds extensive application across multiple industries due to its combination of corrosion resistance, mechanical strength, formability, and hygienic properties:
- Food & Beverage Industry: Sanitary-grade tubing for processing lines, conveyor systems, brewing equipment, and dairy processing (304L, 316L with electropolished or mirror finish).
- Pharmaceutical & Biotechnology: Piping for cleanroom environments, CIP (Clean-In-Place) systems, and bioreactor connections (316L, electropolished).
- Chemical Processing: Transfer lines for aggressive chemicals, acid handling, and reactor internals (316L, 904L, duplex grades).
- Oil & Gas: Downstream processing lines, instrumentation tubing, and marine applications (316L, duplex S31803/S32205).
- Automotive Industry: Exhaust system components, fuel lines, and structural tubing (409, 439, 321).
- Construction & Architecture: Handrails, structural elements, decorative profiles, and elevator components (201, 304, 430).
- Medical Equipment: Surgical instrument handles, hospital furniture, and dialysis machine tubing (316L, electropolished).
- Heat Exchangers & Boilers: Condenser tubes, evaporator coils, and boiler heating elements (304, 321, 347).
- Wire Rope & Spring Manufacturing: Raw material for cold-drawn wire and spring wire production.
6. Quality Certifications & Testing
6.1 Incoming Material Inspection
- Chemical composition analysis (OES spectroscopy) — verified against ASTM/EN standards
- Mill test certificates (MTC) — EN 10204 Type 3.1
- Dimensional verification of strip thickness and width
- Visual inspection for surface defects, rolling marks, and edge quality
6.2 In-Process Quality Control
- Weld Seam Inspection: Visual examination and, where required, radiographic testing (RT) or ultrasonic testing (UT) of weld seams
- Hydrostatic/Pneumatic Testing: Pressure testing at 1.5× the design pressure to verify weld integrity and tube wall soundness
- Dimensional Monitoring: Continuous online measurement of OD, WT, and roundness using laser or mechanical gauges