Stainless Steel Coil Tube — Waste Heat Recovery Grade (Coiltube Series)
Product Overview
The Stainless Steel Coil Tube (hereinafter referred to as "Coiltube") is a precision-engineered continuous tubing product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is specifically designed for high-temperature waste heat recovery systems, particularly coil-type riser configurations employed in heavy industrial environments such as steel-making and metallurgical operations. The Coiltube series is supplied in a pre-formed helical coil configuration, enabling direct integration into heat exchanger assemblies without the need for on-site bending or welding of individual pipe segments, thereby significantly reducing installation time, labor costs, and the risk of workmanship defects.
The design philosophy behind this product draws from the successful application of coil-type riser waste heat recovery systems at major steel enterprises (e.g., Liuzhou Steel), where continuous helical stainless steel tubing is utilized to capture and transfer high-temperature flue gas energy efficiently. The coil geometry maximizes the heat transfer surface area per unit volume, providing superior thermal performance compared to conventional straight-pipe heat exchanger configurations.
Material & Properties
Base Material Grades
- SAE 304 / AISI 304 (UNS S30408) — Austenitic stainless steel with excellent general corrosion resistance; suitable for moderate-temperature waste heat applications (up to 870°C continuous service).
- SAE 321 / AISI 321 (UNS S32108) — Titanium-stabilized austenitic stainless steel; superior resistance to intergranular corrosion and thermal cycling; recommended for elevated-temperature waste heat recovery (up to 900°C continuous service).
- SAE 310 / AISI 310 (UNS S31008) — High-chromium, high-nickel austenitic stainless steel; exceptional oxidation resistance; designed for extreme-temperature environments (up to 1150°C continuous service).
- SAE 316 / AISI 316 (UNS S31603) — Molybdenum-bearing austenitic stainless steel; enhanced resistance to pitting and crevice corrosion; ideal for environments with sulfur compounds or chlorides in flue gas streams.
Key Mechanical and Thermal Properties (AISI 321 Reference)
- Tensile Strength (0.2% Proof Stress): ≥ 205 MPa (at 20°C)
- Elongation: ≥ 40%
- Thermal Conductivity: 16.3 W/(m·K) (at 100°C)
- Specific Heat Capacity: 0.50 kJ/(kg·K)
- Linear Thermal Expansion Coefficient: 16.0 × 10⁻⁶ /°C (20–100°C)
- Density: 7.93 g/cm³
- Maximum Service Temperature: 900°C (oxidation-limited)
- Corrosion Resistance: Excellent resistance to atmospheric, aqueous, and flue gas corrosion; superior resistance to intergranular attack after welding or heat treatment
Specifications
| Parameter | Specification | Standard / Tolerance |
|---|---|---|
| Outer Diameter (OD) | φ12.0 mm – φ51.0 mm (customizable) | ±0.10 mm |
| Wall Thickness | 1.0 mm – 3.5 mm | ±10% of nominal |
| Coil Inner Diameter | φ150 mm – φ600 mm | ±5 mm |
| Coil Length (Continuous) | Up to 2,000 m per coil (continuous) | As per order specification |
| Coil Pitch (Center-to-Center) | 15 mm – 50 mm (configurable) | ±1.0 mm |
| Surface Finish | Pickled & Passivated (2B); optional electropolished | Ra ≤ 0.4 μm (electropolished) |
| End Form | Plain cut; beveled; threaded; socket-weld prepared | Per customer drawing |
| Material Grade Options | 304, 321, 316, 310, 316L, 321H | ASTM A213 / A269 |
| Manufacturing Standard | ASTM A213, ASTM A269, GB/T 14976, GB/T 12771 | — |
| Delivery Condition | Annealed (Solution Treated) | — |
| Coil Packaging | Wooden reel / steel cradle with moisture-proof wrapping | ISO 11607 compliant |
Manufacturing Process
- Raw Material Inspection & Mill Certification: Incoming stainless steel strip or wire rod is verified against ASTM A213/A269 chemical composition requirements. Spectroscopic analysis (OES) confirms elemental content within specified ranges. Mill test certificates (MTC) are cross-referenced.
- Hot Rolling / Cold Drawing: Steel strip is cold-rolled into seamless tube blanks. For tighter tolerances, the tube is cold-drawn through precision dies to achieve the specified OD and wall thickness with uniform dimensional accuracy.
- Heat Treatment (Solution Annealing): Tubes are solution-annealed at 1050–1150°C followed by controlled water quenching. This process eliminates residual stresses from forming, dissolves carbides (particularly in stabilized grades such as 321), and restores full austenitic microstructure for optimal corrosion resistance and ductility.
- Pickling & Passivation: Annealed tubes undergo acid pickling (nitric-hydrofluoric acid blend) to remove oxide scale, followed by passivation treatment to establish a protective chromium oxide surface film (Cr₂O₃ layer, ≥ 200 nm thickness).
- Coil Forming (Continuous Helical Winding): Using a CNC-controlled coil forming machine, the straight tube is continuously wound into a helical coil at a precisely controlled pitch and diameter. The forming process is designed to avoid work hardening and plastic deformation that would compromise the tube's mechanical properties. A mandrel or die system ensures consistent coil geometry without kinking or ovality.
- Dimensional & Non-Destructive Testing (NDT): Each coil undergoes ultrasonic testing (UT) for wall thickness uniformity, eddy current testing (ECT) for surface defect detection, and hydrostatic pressure testing (1.5× maximum working pressure, held for 30 seconds) to verify integrity. Visual inspection confirms surface finish quality.
- Final Inspection & Packaging: Coils are inspected for dimensional accuracy (OD, wall thickness, pitch, coil diameter), surface condition, and end preparation. Each coil is labeled with material grade, heat number, coil dimensions, and traceability information before packaging on wooden reels or steel cradles with moisture-barrier wrapping.
Applications
Primary Application Domain: Waste Heat Recovery Systems
The Coiltube product is specifically engineered for deployment in coil-type riser waste heat recovery systems within steel-making and metallurgical processes. In such systems, the helical stainless steel coil is positioned within high-temperature flue gas streams (e.g., blast furnace gas, basic oxygen furnace (BOF) exhaust, or continuous casting secondary flue gas) to recover thermal energy that would otherwise be lost to the atmosphere.
Specific Application Scenarios
- Steel Industry Waste Heat Recovery: Recovery of high-temperature waste heat from blast furnace stoves, BOF ladle gas, and continuous casting tundish exhaust for preheating of combustion air or feed water.
- Industrial Boiler Economizers: Installation as tube-in-tube heat exchangers for feed water preheating in industrial steam generation systems.
- Chemical Process Heat Exchangers: Use in compact heat exchanger assemblies where high surface-area-to-volume ratios are required for process fluid heating or cooling.
- Power Generation Auxiliary Systems: Application in turbine exhaust heat recovery, feedwater preheating, and steam extraction systems.
- Environmental Flue Gas Treatment: Integration into flue gas desulfurization (FGD) and selective catalytic reduction (SCR) systems where corrosion resistance is critical.
- Oil & Gas Processing: Use in process gas heating/cooling, vapor recovery, and heat integration within refineries and petrochemical complexes.
Performance Advantages in Waste Heat Recovery
In the application of coil-type riser waste heat recovery at large-scale steel enterprises, the stainless steel Coiltube demonstrated the following performance characteristics:
- Waste heat recovery efficiency of 25–40% of total flue gas enthalpy
- Reduction in fuel consumption by 8–15% in associated heating processes
- Service life exceeding 5 years in continuous high-temperature operation (with AISI 321 grade at flue gas temperatures up to 850°C)
- Significant reduction in installation labor compared to conventional straight-pipe heat exchanger assemblies (approximately 60% reduction in on-site welding operations)
Quality Certifications & Compliance
Product Certifications
- ISO 9001:2015 — Quality Management System certification covering the entire manufacturing process from raw material procurement to final dispatch
- ISO 14001:2015 — Environmental Management System certification ensuring environmentally responsible manufacturing practices
- ISO 45001:2018 — Occupational Health and Safety Management System
- NADCAP (National Aerospace and Defense Contractors Accreditation Program) — For aerospace-grade coil tube applications (where applicable)
Material & Product Standards Compliance
- ASTM A213 — Standard Specification for Seamless and Welded Austenistic Stainless Steel and Heat-Resisting Alloy Tubes
- ASTM A269 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and Similar Severe Service
- GB/T 14976 — Seamless Steel Tubes for Fluid Transport (Chinese National Standard)
- GB/T 12771 — Stainless Steel Tubes for General Use (Chinese National Standard)
- EN 10216-5 — European standard for seamless austenitic stainless steel tubes
- JIS G3459 — Japanese Industrial Standard for austenitic stainless steel tubes
Testing & Verification
- Chemical composition analysis via Optical Emission Spectroscopy (OES) — per ASTM E415
- Mechanical testing (tensile, hardness, impact) — per ASTM A370
- Hydrostatic pressure testing — 1.5× maximum design pressure, 30-second hold
- Ultrasonic thickness testing (UT) — per ASTM E797
- Eddy current testing (ECT) for surface defect detection — per ASTM E2307
- Intergranular corrosion testing (IGC) — per ASTM A262 Practice No. 1E (for stabilized grades)
- Pitting corrosion resistance testing — per ASTM G48
- Dimensional verification — laser measurement system with ±0.05 mm resolution
Traceability & Documentation
Each coil tube shipment is accompanied by a complete Mill Test Certificate (MTC) / Enriched Certificate of Conformity (EC) in accordance with EN 10204 Type 3.1, providing full traceability from the steelmaking heat number through all manufacturing stages. The certificate includes chemical composition, mechanical test results, heat treatment parameters, NDT reports, and dimensional verification data.
Unique Selling Points
- Continuous Coil Configuration: Pre-formed helical geometry eliminates on-site bending, welding, and alignment — reducing installation time by up to 60% and eliminating potential failure points at weld joints.
- Proven Industrial Application: Successfully deployed in large-scale waste heat recovery systems at major Chinese steel enterprises, demonstrating reliable long-term performance in demanding metallurgical environments.
- Superior Thermal Performance: The compact helical coil design provides 3–5× greater heat transfer surface area per unit volume compared to conventional straight-pipe heat exchanger configurations.
- Multi-Grade Material Availability: Comprehensive range of austenitic stainless steel grades (304, 321, 316, 310) enables precise material selection matched to specific temperature and corrosion conditions.
- Full Traceability: Complete manufacturing traceability from raw material heat number through final product, supporting compliance with international quality management and regulatory requirements.
- Customization Capability: Flexible customization of OD, wall thickness, coil pitch, coil diameter, and total length to meet specific engineering design requirements.