Stainless Steel Coil Tube (Coiltube) — Product Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (also referred to as Coiltube or Coiled Tubing) is a continuous-length tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. Unlike conventional cut-length seamless or welded pipes, coil tubes are produced in continuous helical coils, enabling efficient downstream processing with minimal material waste. This product category is extensively used in heat exchangers, condensers, evaporators, refrigeration systems, and fluid transport networks where flexibility, corrosion resistance, and thermal conductivity are paramount.
Coil tubes offer distinct advantages over straight-length pipes, including reduced welding joints (enhancing system integrity), improved flexibility during installation, and superior heat transfer performance due to the inherent coiling geometry that promotes turbulent flow. The safety analysis of coil tubes and coil piping systems encompasses structural integrity under cyclic loading, thermal stress resistance, corrosion fatigue behavior, and long-term reliability under operational conditions.
2. Material & Properties
Coil tubes supplied by Wenzhou Jixing are manufactured from a range of austenitic, ferritic, and duplex stainless steel grades, each selected based on the end-use application requirements:
- SAE 304 / AISI 304 (UNS S30400) — General-purpose austenitic stainless steel with excellent corrosion resistance and formability. Suitable for food-grade, chemical, and cryogenic applications.
- SAE 316 / AISI 316 (UNS S31600) — Molybdenum-enhanced austenitic grade offering superior resistance to pitting and crevice corrosion. Ideal for marine, pharmaceutical, and aggressive chemical environments.
- SAE 321 / AISI 321 (UNS S32100) — Titanium-stabilized austenitic grade with enhanced resistance to intergranular corrosion. Recommended for high-temperature applications up to 870°C.
- SAE 316L / AISI 316L (UNS S31603) — Low-carbon variant of 316 with improved weldability and resistance to sensitization during welding operations.
- SAE 310S / AISI 310S (UNS S31008) — High-temperature austenitic grade with outstanding oxidation resistance, suitable for furnace components and heat exchanger tubes exceeding 1000°C.
2.1 Typical Mechanical Properties (Annealed Condition)
| Property | SAE 304 / 304L | SAE 316 / 316L | SAE 321 | SAE 310S |
|---|---|---|---|---|
| Tensile Strength (MPa) | ≥ 515 | ≥ 515 | ≥ 515 | ≥ 515 |
| Yield Strength (0.2% offset, MPa) | ≥ 205 | ≥ 205 | ≥ 205 | ≥ 205 |
| Elongation (%) | ≥ 40 | ≥ 40 | ≥ 40 | ≥ 40 |
| Hardness (HBW max) | ≤ 201 | ≤ 217 | ≤ 217 | ≤ 217 |
| Density (g/cm³) | 8.00 | 8.00 | 8.00 | 8.00 |
| Thermal Conductivity (W/m·K, 100°C) | 16.3 | 14.6 | 16.3 | 14.6 |
| Maximum Service Temperature (°C) | 870 | 870 | 900 | 1150 |
2.2 Chemical Composition (wt%, Typical)
| Element | SAE 304 | SAE 316 | SAE 321 | SAE 310S |
|---|---|---|---|---|
| C (Carbon) | ≤ 0.08 | ≤ 0.08 | ≤ 0.08 | ≤ 0.08 |
| Cr (Chromium) | 18.0–20.0 | 16.0–18.0 | 18.0–20.0 | 24.0–26.0 |
| Ni (Nickel) | 8.0–10.5 | 10.0–14.0 | 9.0–12.0 | 19.0–22.0 |
| Mo (Molybdenum) | — | 2.0–3.0 | — | — |
| Ti (Titanium) | — | — | 5×C to 0.70 | — |
| Si (Silicon) | ≤ 1.00 | ≤ 1.00 | ≤ 1.00 | ≤ 1.50 |
| S (Sulfur) | ≤ 0.030 | ≤ 0.030 | ≤ 0.030 | ≤ 0.030 |
3. Dimensions & Specifications
Wenzhou Jixing Metal Materials Co., Ltd. offers a comprehensive range of coil tube dimensions conforming to international standards including ASTM A213, ASTM A269, ASTM A554, EN 10217, EN 10216-5, and JIS G3459. The following table presents typical dimensional specifications:
| Parameter | Specification Range |
|---|---|
| Outer Diameter (OD) | 3.18 mm – 50.8 mm (⅛" – 2") |
| Wall Thickness | 0.30 mm – 3.00 mm |
| Coil Length (Continuous) | Up to 1000 m per coil (custom lengths available) |
| Coil Diameter (Outer) | 300 mm – 1500 mm |
| Surface Finish | 2B (Cold Rolled & Annealed), No. 4 Brushed, Mirror (8K), Matte |
| End Form | Plain, Beveled, Threaded, or Flanged |
| Manufacturing Method | Seamless (Cold Drawing) or ERW (Electric Resistance Welded) |
| Temperature Range | −196°C (Cryogenic) to +1150°C (Oxidation Limit) |
| Pressure Rating | Up to 40 MPa (dependent on OD, wall thickness, and grade) |
| Dimensional Tolerance | OD: ±0.05 mm; Wall: ±10% (per ASTM A213) |
4. Manufacturing Process
The production of high-quality stainless steel coil tubes follows a rigorously controlled multi-stage manufacturing process designed to ensure metallurgical integrity, dimensional accuracy, and surface quality:
- Raw Material Procurement: Virgin stainless steel billets or continuously cast slabs are sourced from certified mills. Incoming materials undergo spectrographic analysis (OES — Optical Emission Spectroscopy) to verify chemical composition compliance.
- Hot Rolling: Billets are heated to approximately 1100–1200°C and hot-rolled into semi-finished tubes or strips, depending on the manufacturing route (seamless vs. welded).
- Pickle & Anneal: The hot-rolled product undergoes acid pickling to remove oxide scales, followed by solution annealing in a protective atmosphere (N₂ or H₂) to restore the austenitic microstructure and eliminate residual stresses.
- Cold Drawing / Cold Forming: Tubes are cold-drawn through precision dies to achieve final OD and wall thickness specifications. For welded coil tubes, cold-rolled strips are formed into tubes and welded via the ERW (Electric Resistance Welding) process with inline ultrasonic weld inspection.
- Final Annealing & Pickling: Cold-worked tubes undergo a final solution anneal (typically 1050–1100°C) to achieve the desired mechanical properties, followed by pickling and passivation to establish a uniform chromium oxide passive film.
- Coiling: The finished tube is wound onto a steel coil mandrel using a precision coiling head to maintain consistent coil diameter and prevent mechanical damage to the tube surface.
- Quality Inspection: Each coil undergoes comprehensive non-destructive testing (NDT) including ultrasonic testing (UT) for wall thickness verification, eddy current testing (ECT) for surface and subsurface defect detection, hydrostatic pressure testing per ASTM A213, and visual inspection.
- Packaging & Dispatch: Coils are protected with waterproof wrapping, desiccant bags, and wooden or steel shipping crates to prevent corrosion and mechanical damage during transit.
5. Safety Analysis & Reliability Assessment
The safety performance of stainless steel coil tubes and coil piping systems is evaluated through the following engineering considerations:
- Cyclic Fatigue Resistance: Coil tubes subjected to repeated bending during installation and operation must demonstrate adequate fatigue life. The austenitic microstructure of grades such as 304 and 316 provides excellent fatigue crack propagation resistance due to its face-centered cubic (FCC) crystal structure, which supports multiple slip systems and dislocation mobility.
- Thermal Stress Management: In heat exchanger applications, differential thermal expansion between the coil tube and the supporting structure must be accommodated. The coefficient of thermal expansion for austenitic stainless steels (approximately 17.3 × 10⁻⁶ /°C) is higher than that of carbon steel, necessitating proper expansion joint design.
- Corrosion Fatigue: In chloride-containing environments, the combined action of cyclic loading and localized corrosion can accelerate failure. The selection of molybdenum-bearing grades (316, 316L, 2205 duplex) is recommended for such service conditions to mitigate pitting and crevice corrosion initiation sites.
- Hydrogen Embrittlement Resistance: Austenitic stainless steels are inherently resistant to hydrogen embrittlement, making them suitable for hydrogen service environments where ferritic or martensitic grades would be susceptible to delayed fracture.
- Creep Resistance at Elevated Temperatures: For applications exceeding 600°C, the creep strength of the selected grade must be verified. Grade 310S and precipitation-hardened alloys (e.g., 17-4 PH) are preferred for prolonged high-temperature service.
Key Safety Principle: The continuous coil configuration of the tube inherently reduces the number of field-welded joints compared to equivalent straight-length pipe installations. This reduction in welded connections directly decreases the probability of leak points and enhances the overall structural integrity of the piping system, as welds represent the most common failure initiation sites in industrial piping networks.
6. Applications
Stainless steel coil tubes from Wenzhou Jixing Metal Materials Co., Ltd. find extensive application across multiple industrial sectors:
- Heat Exchangers & Condensers: Coil tubes serve as the primary heat transfer elements in shell-and-tube heat exchangers, air coolers, and process condensers in petrochemical, power generation, and HVAC systems.
- Refrigeration & Cryogenic Systems: The excellent low-temperature toughness of austenitic grades (retaining full ductility down to −196°C) makes coil tubes ideal for ammonia, refrigerant, and LNG (Liquefied Natural Gas) transfer systems.
- Food & Beverage Processing: Sanitary-grade coil tubes (electropolished, Ra ≤ 0.25 μm) are used in dairy processing, brewing, and pharmaceutical equipment where hygienic standards (FDA, 3-A Sanitary) are mandatory.
- Chemical Processing: Corrosion-resistant coil tubes handle aggressive chemicals including acids, alkalis, and halogenated compounds in continuous processing lines.
- Automotive Industry: Coil tubes are employed in exhaust system components, fuel injection lines, and turbocharger cooling circuits.
- Oil & Gas Industry: Used in subsea production systems, chemical injection lines, and offshore platform piping where corrosion resistance and fatigue performance are critical.
- Medical & Laboratory Equipment: Autoclave tubes, medical gas delivery systems, and analytical instrument flow paths utilize high-purity coil tubes.
- Architecture & Decoration: Decorative coil tubes in 8K mirror finish are used for handrails, balustrades, and architectural cladding systems.
7. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains rigorous quality management systems and holds the following certifications and compliance standards:
- ISO 9001:2015 — Quality Management System certification ensuring consistent product quality and customer satisfaction.
- ISO 14001:2015 — Environmental Management System certification demonstrating environmental responsibility in manufacturing operations.
- ISO 45001:2018 — Occupational Health and Safety Management System certification.
- EN 10204 3.1 Certificate — Third-party inspection and testing certificates provided for each batch upon request.
- ASTM / ASME Compliance — Products manufactured in accordance with ASTM A213, A269, A5