Stainless Steel Coil Tube (Coiltube) — Product Technical Specification
1. Product Overview
The Stainless Steel Coil Tube, designated as product series 490 by Wenzhou Jixing Metal Materials Co., Ltd., is a precision-engineered continuous-length tubular product formed into a compact coil configuration. Unlike conventional straight-length seamless or welded stainless steel pipes, the coil tube is manufactured in a continuous helical or serpentine winding format, which offers significant advantages in terms of material utilization, shipping efficiency, and installation flexibility.
This product line is specifically designed for applications requiring high thermal transfer efficiency, corrosion resistance, and mechanical durability — most notably in the Cargo Oil Heating System domain, where coil tubes serve as the core heat exchange elements for heating viscous crude oils and refined petroleum products during maritime and industrial transport.
Key Distinction: The coil tube format eliminates the need for on-site bending and welding, reducing installation time by up to 40% compared to straight pipe segments. The continuous coil structure also provides inherent stress-relief properties that enhance fatigue resistance under cyclic thermal loading conditions.
2. Material & Properties
2.1 Base Alloy Grades
The stainless steel coil tube is available in multiple austenitic and duplex alloy grades, selected according to the operational environment and fluid characteristics:
- ASTM A213 TP304 / TP304L — General-purpose austenitic stainless steel offering excellent corrosion resistance and formability. The "L" (low carbon) variant minimizes intergranular sensitization risk during welding.
- ASTM A213 TP316 / TP316L — Enhanced molybdenum content (2.0–3.0% Mo) provides superior resistance to chlorides, sulfides, and acidic environments commonly encountered in cargo oil systems.
- ASTM A213 TP321 / TP347 — Stabilized grades (Ti/Cb stabilized) suitable for sustained high-temperature service exceeding 600°C.
- ASTM A213 TP310S — High-temperature grade for extreme thermal cycling applications in heavy fuel oil (HFO) heating systems.
- ASTM A213 TP317L — Ultra-high molybdenum (3.0–4.0%) grade for aggressive chemical and marine environments.
2.2 Mechanical Properties
- Tensile Strength (UTS): ≥ 515 MPa (75 ksi) minimum per ASTM A213
- Yield Strength (0.2% offset): ≥ 205 MPa (30 ksi) minimum
- Elongation: ≥ 35% in 50 mm (2 in.) gauge length
- Hardness: ≤ 223 HB (Rockwell B scale equivalent)
- Thermal Conductivity: 14.6–16.3 W/(m·K) at 20°C (varies by grade)
- Thermal Expansion Coefficient: 16.0–18.0 × 10⁻⁶ /°C (20–100°C)
2.3 Surface Finish Options
- 2B Finish — Standard cold-rolled, annealed, and pickled surface
- No. 4 Brushed Finish — Uniform unidirectional grain for aesthetic and anti-corrosion applications
- Electropolished (EP) Finish — Ra ≤ 0.25 μm for sanitary and chemical processing applications
- Pickle & Passivate (P&P) — Enhanced passive oxide layer for maximum corrosion protection
3. Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 3.0 mm – 108 mm (1/8" – 4") | ASTM A213 / ASME B36.19M |
| Wall Thickness (WT) | 0.25 mm – 6.0 mm (0.010" – 0.236") | ASTM A213 / EN 10216-5 |
| Coil Length (Continuous) | 50 m – 500 m (164 ft – 1,640 ft) per coil | Manufacturer specification |
| Coil Inner Diameter (Winding ID) | 150 mm – 600 mm (6" – 24") | Per customer requirement |
| Tolerance on OD | ±0.05 mm for OD ≤ 10 mm; ±0.10 mm for OD > 10 mm | ASTM A213 |
| Tolerance on WT | ±10% of nominal wall thickness | ASTM A213 |
| Bend Radius (Minimum) | ≥ 3D (where D = OD of tube) | ISO 13890 |
| Operating Temperature Range | −196°C to +1100°C (depending on grade) | Grade-dependent |
| Maximum Working Pressure | Up to 40 bar (580 psi) at 25°C | ASME BPV Code Section VIII |
| End Condition | Plain end, beveled end, or threaded end (per request) | Customer specification |
| Heat Treatment | Solution annealed at 1050°C – 1150°C followed by water quench | ASTM A213 |
| Coating / Lining | Available upon request (PTFE, PFA, ceramic coating) | Custom specification |
4. Manufacturing Process
The production of stainless steel coil tubes follows a rigorous multi-stage manufacturing protocol to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Preparation: High-purity stainless steel ingots or slabs are produced via the Vacuum Arc Remelting (VAR) or Electro-Slag Remelting (ESR) process to ensure homogeneity and minimal inclusions. Raw steel is certified with a full Chemical Composition (CC) report.
- Hot Rolling & Piercing: Billets are reheated to 1200°C – 1250°C and hot-rolled into seamless tube blanks. The piercing operation creates the initial hollow cross-section. This stage establishes the base dimensions and eliminates surface defects.
- Hot Extrusion (Alternative Route): For larger diameters or thicker walls, hot extrusion through calibrated dies is employed, providing superior dimensional control compared to piercing.
- Cold Drawing & Mandrel Drawing: The hot-rolled tube is cold-drawn through precision tungsten carbide dies to achieve the final OD and wall thickness tolerances. Mandrel drawing ensures internal surface smoothness and eliminates the internal seam found in standard drawing.
- Solution Annealing: Tubes are annealed in a controlled atmosphere furnace (N₂ or H₂ atmosphere, dew point ≤ −60°C) at temperatures between 1050°C and 1150°C, followed by rapid water quenching. This eliminates residual stresses, dissolves carbides, and restores full austenitic microstructure.
- Pickling & Passivation: Annealed tubes undergo acid pickling (HNO₃ + HF or H₂SO₄ + HNO₃ blend) to remove scale and oxide layers, followed by nitric acid passivation to regenerate the chromium oxide passive film.
- Coil Winding: The continuous tube is precisely wound onto a coil former using CNC-controlled winding equipment. Tension is carefully controlled to prevent ovality, kinking, or residual deformation. The winding radius and pitch are set according to the target application (e.g., helical coil for heat exchangers, serpentine coil for cold-plate systems).
- Non-Destructive Testing (NDT): Every coil undergoes 100% inspection including:
- Eddy Current Testing (ECT) per ASTM E309 for wall thickness measurement and defect detection
- Magnetic Particle Inspection (MPI) for surface and near-surface defects
- Visual inspection per ASTM E1019 for surface quality and dimensional conformance
- Packaging & Shipping: Coils are wrapped with moisture-proof kraft paper, plastic film, and secured with steel strapping. Shipping is in wooden crates or on reinforced coil spools to prevent deformation during transit.
5. Applications
5.1 Cargo Oil Heating Systems (Primary Application)
The coil tube is the fundamental component in Cargo Oil Heating Systems used aboard oil tankers, product carriers, and chemical tankers. In these systems, hot water or steam circulates through the stainless steel coil tubes to heat viscous crude oil or refined petroleum products, reducing their viscosity to enable pumping and transfer. Key design considerations include:
- Heat Transfer Efficiency: The coil configuration maximizes surface area-to-volume ratio, enabling rapid heat exchange. Stainless steel's moderate thermal conductivity combined with its corrosion resistance makes it ideal for this duty.
- Thermal Cycling Resistance: Cargo heating systems experience repeated heating and cooling cycles. The solution-annealed austenitic microstructure of the coil tube provides excellent resistance to thermal fatigue.
- Sulfide Stress Corrosion Resistance (SSCR): Crude oils containing H₂S can cause sulfide stress cracking in susceptible materials. TP316L and TP317L coil tubes offer proven resistance to this degradation mechanism.
- Temperature Uniformity: The continuous coil winding ensures uniform heat distribution across the cargo hold, preventing localized overheating that could cause oil degradation or safety hazards.
5.2 Additional Applications
- Marine Heat Exchangers: Seawater-cooled condensers and evaporators in shipboard HVAC systems
- Chemical Processing: Reactor jacket cooling coils, distillation column internals, and heat recovery systems in petrochemical plants
- Power Generation: Boiler economizer tubes, condenser tube bundles, and superheater coils in thermal power plants
- Food & Beverage Industry: Sanitary-grade coil heat exchangers for pasteurization, sterilization, and thermal processing (EP finish, 316L grade)
- Pharmaceutical Manufacturing: Clean-in-Place (CIP) compatible coil systems for reactor temperature control
- Automotive & Aerospace: Fuel cooling systems, hydraulic fluid conditioning, and thermal management coils
- Oil & Gas Offshore Platforms: Subsea heating coils for pipeline flow assurance in cold-water environments
- Refrigeration & HVAC: Evaporator and condenser coils for industrial refrigeration systems
6. Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system aligned with international standards. The stainless steel coil tube product line is certified and compliant with the following:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification covering design, manufacturing, and delivery processes |
| ISO 14001:2015 | Environmental Management System ensuring sustainable and environmentally responsible production |
| ISO 45001:2018 | Occupational Health and Safety Management System |
| ASME / NB (National Board) | Pressure vessel and piping components certification for ASME BPV Code applications |
| DNV-GL / ABS / DNV | Classification society approval for marine applications (cargo heating systems, marine heat exchangers) |
| EN 10204 3.1 / 3.2 | Inspection documentation — 3.1 (inspection certificate by authorized QC inspector) or 3.2 (inspection certificate with independent third-party verification) |
| API 5L / API 5CT | Compliance for oil and gas industry applications where applicable |
| CE Marking | Conformity with European directives (Pressure Equipment Directive PED 2014/68/EU, Machinery Directive 2006/42/EC) |
| Mill Test Reports (MTR) | Every production lot accompanied by full MTR including chemical composition, mechanical properties, heat treatment record, and NDT results |
| Material Traceability | Full traceability from raw steel ingot heat number through to finished coil, enabling complete product lineage documentation |
7. Unique Selling Points
- Continuous Coil Configuration: Eliminates field welding and joint-related failure points, significantly improving system reliability and reducing maintenance costs over the operational lifecycle.
- Grade Flexibility: Availability in over 10 stainless steel grades enables precise material matching to specific service conditions — from standard 304L for general duty to 317L for aggressive chloride environments.
- Dimensional Precision: Cold-drawing and CNC-controlled winding ensure OD tolerances within ±0.05 mm and consistent wall thickness throughout the entire coil length.
- Proven Marine Application Heritage: Extensive track record in cargo oil heating systems for oil tankers and product carriers, with classification society approvals from DNV-GL, ABS, and other major registrars.
- Full Traceability & Documentation: Every coil is backed by complete mill test reports, NDT certificates, and material traceability records — meeting the stringent documentation requirements of ASME, EN, and classification society standards.
- Custom Winding Profiles: Capability to produce helical, serpentine, spiral, or custom-wound configurations tailored to specific heat exchanger designs and installation constraints.
- Post-Processing Options: Available with electropolishing, P&P treatment, or specialized coatings (PTFE, ceramic) for enhanced performance in specific service environments.
8. Design Considerations for Cargo Oil Heating System Integration
Engineering Note: When integrating stainless steel coil tubes into cargo oil heating systems, the following design principles must be observed to ensure safe and efficient operation:
- Thermal Expansion Accommodation: The coil tube assembly must include expansion loops or bellows to absorb differential thermal expansion between