Stainless Steel Coil Tube (Coiltube) — Technical Product Specification
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered continuous-length tubular product supplied in coiled form for downstream processing and installation. Unlike conventional cut-length tubing, coil tubes are formed into continuous helical coils, enabling seamless integration into automated fabrication lines, heat exchanger assemblies, HVAC (Heating, Ventilation, and Air Conditioning) systems, and process piping networks.
This product is designed to serve as a core component in fan coil unit (FCU) systems, humidification circuits, and thermal management applications where corrosion resistance, thermal conductivity, and mechanical integrity are paramount. The coil configuration minimizes material waste during downstream forming, welding, and bending operations, offering significant economic advantages over straight-length alternatives.
2. Material & Properties
2.1 Base Material Grades
- AISI 304 (UNS S30408) — General-purpose austenitic stainless steel with excellent corrosion resistance, weldability, and formability. Ideal for HVAC, food-grade, and marine environments.
- AISI 316 (UNS S31608) — Molybdenum-enhanced austenitic grade offering superior resistance to chlorides, acids, and aggressive chemical media.
- AISI 316L (UNS S31603) — Low-carbon variant of 316, optimized for welding applications where sensitization and intergranular corrosion must be avoided.
- AISI 321 (UNS S32108) — Titanium-stabilized grade suitable for elevated-temperature applications (up to 870 °C) with resistance to thermal cycling.
2.2 Mechanical Properties (Typical for Grade 304, Annealed Condition)
| Property | Symbol | Value | Test Standard |
|---|---|---|---|
| Tensile Strength (Ultimate) | UTS | ≥ 515 MPa (74,700 psi) | ASTM A269 / A213 |
| Yield Strength (0.2% Offset) | YS | ≥ 205 MPa (29,700 psi) | ASTM A269 / A213 |
| Elongation (in 50 mm) | El | ≥ 40% | ASTM A269 / A213 |
| Hardness (Rockwell B) | HRB | ≤ 95 | ASTM E140 |
| Density | ρ | 8.00 g/cm³ | — |
| Thermal Conductivity (at 20 °C) | k | 16.3 W/(m·K) | ASTM E153 |
| Thermal Expansion Coefficient (20–100 °C) | α | 17.3 × 10⁻⁶ /K | ASTM E228 |
2.3 Chemical Composition (Grade 304, wt%)
| Element | C | Mn | P | S | Si | Ni | Cr | N | Fe |
|---|---|---|---|---|---|---|---|---|---|
| Max / Spec | 0.08 | 2.00 | 0.045 | 0.030 | 1.00 | 8.00–10.50 | 18.00–20.00 | — | Balance |
2.4 Surface Finish Options
- 2B Finish — Cold-rolled, annealed, and pickled; matte, non-directional appearance. Standard for general industrial use.
- No. 4 Finish (Brushed) — Lightly ground with uniform directional grain; suitable for visible architectural and decorative applications.
- Mirror Finish (8K) — Polished to a reflective surface (Ra ≤ 0.05 μm); used in pharmaceutical and food processing.
- Pickled & Passivated (P&P) — Free of scale, decarburized layer, and contaminants; enhanced corrosion resistance for chemical service.
3. Specifications
3.1 Dimensional Parameters
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | Φ6.0 mm – Φ159.0 mm | ASTM A269 / A213 / GB/T 12771 |
| Wall Thickness (WT) | 0.4 mm – 8.0 mm | ASTM A269 / A213 / GB/T 12771 | OD Tolerance | ±0.10 mm (≤ Φ25 mm); ±0.15% (＞ Φ25 mm) | ASTM A269 |
| WT Tolerance | ±10% (as-rolled); ±5% (cold-drawn) | ASTM A269 |
| Coil Length (Continuous) | 50 m – 500 m (customizable) | — |
| Coil Inner Diameter (ID) | Φ300 mm / Φ500 mm / Φ600 mm | Customer-specified |
| Maximum Coil Weight | Up to 5,000 kg per coil | — |
| End Condition | Plain cut / Beveled / Sealed with caps | Customer-specified |
| Roundness | ≤ 0.5% of OD | ASTM A269 |
| Straightness (per 1,000 mm) | ≤ 1.0 mm | ASTM A269 |
3.2 Common Size Series (Selected)
| Nominal Size (DN) | OD (mm) | WT (mm) | Equivalent (inch) |
|---|---|---|---|
| DN6 | 6.0 | 0.5 – 1.5 | 1/4" |
| DN8 | 8.0 | 0.8 – 2.0 | — |
| DN10 | 10.0 | 1.0 – 2.5 | — |
| DN15 | 15.9 | 1.5 – 4.0 | 1/2" |
| DN20 | 21.3 | 1.5 – 4.0 | 3/4" |
| DN25 | 26.7 | 1.5 – 5.0 | 1" |
| DN32 | 33.4 | 2.0 – 6.0 | 1-1/4" |
| DN40 | 42.4 | 2.0 – 8.0 | 1-1/2" |
| DN50 | 48.3 | 2.0 – 8.0 | 2" |
| DN80 | 88.9 | 3.0 – 8.0 | 3" |
| DN100 | 114.3 | 3.0 – 8.0 | 4" |
| DN150 | 159.0 | 3.0 – 8.0 | 6" |
4. Manufacturing Process
4.1 Process Flow
- Hot-Rolled Billet Preparation — Primary steelmaking via EAF (Electric Arc Furnace) or AOD (Argon Oxygen Decarburization) refining; continuous casting into billets.
- Hot-Rolling — Billets are reheated to 1,100–1,200 °C and hot-rolled into seamless pipe blanks with controlled dimensional tolerances.
- Pickling & Annealing — Hot-rolled scale is removed via acid pickling (HNO₃ + HF blend); austenitic annealing at 1,050–1,100 °C followed by controlled cooling to achieve the desired grain structure.
- Cold Drawing / Cold Reduction — Tubes are cold-drawn through precision dies to achieve final OD, WT, and surface finish. This step provides dimensional accuracy within ±0.10 mm.
- Intermediate Annealing — Stress-relief annealing at 1,050 °C to restore ductility after cold working, enabling further forming without cracking.
- Final Cold Drawing & Sizing — Final dimensional pass through calibrated mandrels and dies; ensures roundness, straightness, and surface quality.
- Coiling — Continuous tubing is wound onto precision-engineered coil stands under controlled tension (typically 5–15 kN depending on diameter and wall thickness). Coiling tension is carefully managed to prevent ovalization and surface damage.
- Surface Treatment — Final pickling, passivation, or mechanical polishing per customer specification.
- Quality Inspection — 100% inline inspection including dimensional measurement, surface defect detection (eddy current or ultrasonic), and hydrostatic pressure testing.
- Packaging & Shipping — Coils are wrapped in moisture-proof film, secured with steel strapping, and palletized for export or domestic delivery.
4.2 Key Process Controls
- Coiling tension is regulated via closed-loop servo systems to maintain uniform coil set and prevent permanent deformation.
- Online ultrasonic thickness gauging monitors wall thickness at frequencies of 50–100 kHz throughout production.
- Hydrostatic pressure testing at 5–10× working pressure ensures weld integrity and eliminates porosity defects.
- Grain boundary analysis (GBA) per ASTM A269 confirms proper heat treatment and absence of sensitization.
5. Applications
5.1 HVAC & Thermal Management
Coil tubes are integral to fan coil units (FCUs), air handling units (AHUs), and chiller coils. The continuous coil form allows automated U-bend or serpentine coil forming without additional welding, reducing leak points and improving thermal efficiency. In humidification systems, stainless steel coil tubes resist corrosion from water and chemical additives.
5.2 Food & Beverage Processing
Used in pasteurization circuits, CIP (Clean-In-Place) systems, brewing equipment, and sanitary piping. The non-reactive surface of austenitic stainless steel prevents product contamination and facilitates hygienic cleaning.
5.3 Pharmaceutical & Bioprocessing
Compliant with FDA 21 CFR and EU GMP (Good Manufacturing Practice) requirements. Mirror-finish coil tubes are employed in reactor jackets, heat exchangers, and process piping where product contact integrity is critical.
5.4 Chemical & Petrochemical Industry
Grade 316L coil tubes are used in acid handling systems, chemical reactors, and offshore platforms where chloride-induced pitting and crevice corrosion are concerns.
5.5 Marine & Offshore
Resistance to saltwater corrosion makes stainless steel coil tubes suitable for desalination plants, ballast water systems, and marine heat exchangers.
5.6 Architectural & Decorative
Polished coil tubes are used for handrails, balustrades, decorative trim, and structural elements in modern architecture, combining aesthetic appeal with structural performance.
5.7 Automotive & Aerospace
Lightweight, high-strength coil tubing is used in fuel lines, brake lines, turbocharger systems, and hydraulic circuits where space constraints and corrosion resistance are critical.
6. Quality Certifications & Standards Compliance
6.1 Applicable Standards
| Standard | Description | Relevance |
|---|---|---|
| ASTM A269 | Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubes for Chemical and Similar Severe Service Applications | Primary product specification |
| ASTM A213 | Standard Specification for Seamless Austenitic Chromium-Nickel Stainless Steel Tubing for High-Temperature Service | High-temperature applications |
| ASME SB 167 | Specification for Seamless Austenitic Chromium-Nickel Stainless Steel Tube, Heat-Exchanger and Condenser Tube | Pressure vessel applications |
| EN 10216-5 | Non-ferrous metallic tubes — Heat exchangers and related products — Technical delivery conditions — Part 5: Austenitic and austenitic-ferritic stainless steel tubes | European market compliance |
| GB/T 12771 | Seamless Stainless Steel Tubes for Fluid Transport | Chinese national standard |
| GB/T 14976 | Seamless Stainless Steel Tubes for Fluid Transport (Chinese equivalent) | Chinese domestic specification |
| ISO |