Stress-Free Coiled Stainless Steel Tube for Waste Heat Recovery Systems
Product Overview
The stress-free coiled stainless steel tube (Coiltube) is a precision-engineered tubular product designed specifically for waste heat recovery applications, particularly in high-temperature industrial environments. Developed by Wenzhou Jixing Metal Materials Co., Ltd. (Serial No. 386), this coiltube product is manufactured to eliminate residual internal stresses that commonly occur during conventional coiling processes. The stress-free coiling technology ensures superior dimensional stability, enhanced fatigue resistance, and extended service life under thermal cycling conditions.
This product is particularly suited for Rising Pipe Waste Heat Recovery Devices (余热回收上升管装置), where the coiled geometry maximizes heat transfer surface area within compact installation footprints. The elimination of residual stress is critical in preventing deformation, cracking, and premature failure during prolonged exposure to elevated temperatures and thermal gradients.
Material & Properties
Material Grades
- Austenitic Stainless Steels: SUS304 (ASTM 304), SUS316L (ASTM 316L) — offering excellent corrosion resistance and high-temperature oxidation resistance
- Heat-Resistant Stainless Steels: SUS310S (ASTM 310S), SUS309S — designed for sustained operation above 900°C with superior thermal stability
- Super-Austenitic Grades: SUS316Ti, SUS321 (ASTM 321) — enhanced intergranular corrosion resistance for high-temperature service
Key Mechanical Properties
- Tensile Strength (抗拉强度): ≥ 520 MPa (minimum, at room temperature)
- Yield Strength (屈服强度): ≥ 205 MPa (0.2% offset)
- Elongation (延伸率): ≥ 40% (minimum, in annealed condition)
- Residual Stress Level: < 30 MPa (post stress-relief annealing, verified by X-ray diffraction method)
- Creep Resistance (蠕变抗力): Maintains structural integrity at 800–1100°C for extended operational periods
- Thermal Expansion Coefficient (热膨胀系数): 16–18 × 10⁻⁶ /°C (20–900°C)
Corrosion Resistance
- Resistance to sulfuric acid, nitric acid, and organic acids at moderate concentrations and temperatures
- Superior resistance to pitting and crevice corrosion in chloride-containing environments (particularly 316L grade)
- Outstanding resistance to intergranular corrosion following sensitization at 650–850°C
- High-temperature oxidation resistance with scale formation rate < 1 mg/dm²·h at 1000°C (310S grade)
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | Φ6.0 – Φ50.8 mm | ASTM A213 / GB/T 12771 |
| Wall Thickness (WT) | 0.5 – 3.0 mm | ASTM A269 / GB/T 13296 |
| Coil Inner Diameter | Φ200 – Φ2000 mm | Customer-specific |
| Coil Length | 10 – 200 m per coil | Customizable |
| Surface Finish | No. 1, 2B, BA (Bright Annealed), Pickled | ASTM A478 |
| Surface Roughness (Ra) | 0.2 – 1.6 μm | ISO 4287 |
| Heat Treatment Condition | Solution Annealed + Stress-Relief Annealed | ASTM A312 |
| Maximum Service Temperature | Up to 1150°C (310S), 870°C (304/321) | Manufacturer's data |
| Tolerance on OD | ±0.15 mm (≤ Φ25.4 mm); ±0.25 mm (> Φ25.4 mm) | ASTM A213 |
| Tolerance on WT | ±10% of nominal | GB/T 12771 |
| Forming Method | Seamless (Seamless Coiling) / Welded (TPAW) | ASTM A269 / A213 |
| Residual Stress | < 30 MPa (measured by X-ray sin²ψ method) | Internal specification |
Manufacturing Process
Process Flow
- Raw Material Preparation: Selection of certified stainless steel billets or strip material conforming to the specified grade, with verified chemical composition (spectroscopic analysis per ASTM E1086).
- Hot Rolling / Cold Drawing: Production of seamless tube blank via pierce mill and continuous tube mill, or cold-drawn tube from precision-drawn wire/strip.
- Solution Annealing: Heating to 1050–1150°C followed by rapid water or air quenching to achieve full austenitic microstructure and maximize corrosion resistance.
- Coiling Operation: Controlled coiling using precision-guided rollers with tension-controlled winding to produce uniform coil geometry without introducing geometric defects.
- Stress-Relief Annealing (Key Differentiator): Post-coiling thermal treatment at 650–800°C for 1–4 hours (depending on wall thickness and coil diameter) followed by controlled cooling. This critical step eliminates residual stresses induced during coiling, achieving stress levels below 30 MPa.
- Surface Treatment: Pickling and passivation (acid pickling with HNO₃/HF solution) or mechanical polishing to achieve specified surface finish and chromium oxide passive layer.
- Dimensional Inspection: Laser scanning of OD, wall thickness, straightness, and coil geometry verification against tolerance specifications.
- Non-Destructive Testing (NDT): 100% eddy current inspection (ASTM E309), hydrostatic pressure testing (ASTM A530), and visual inspection of weld seams (if applicable).
Stress-Relief Technology
The distinguishing feature of this product is the post-coiling stress-relief annealing process. Conventional coiltubes retain significant residual stresses (typically 80–150 MPa) from the coiling operation, which can lead to:
- Dimensional instability during thermal cycling
- Stress Corrosion Cracking (SCC) susceptibility in chloride environments
- Premature fatigue failure under cyclic thermal loading
- Post-installation deformation affecting heat transfer efficiency
The stress-relief annealing process at Wenzhou Jixing Metal Materials Co., Ltd. systematically eliminates these concerns, producing a tube product with residual stress levels comparable to those of straight, heat-treated tubing — while retaining the compact, high-surface-area geometry of a coiled configuration.
Applications
Primary Application: Waste Heat Recovery Systems
The coiltube is extensively deployed in Waste Heat Recovery Devices (余热回收装置), particularly in rising pipe configurations where:
- Flue gas from industrial furnaces, boilers, and combustion processes passes through the coiled tube array
- Thermal energy is transferred to a working fluid (water, thermal oil, or supercritical CO₂) circulating through the tube interior
- Heat recovery efficiency reaches 85–95% depending on temperature differential and flow configuration
Industry-Specific Applications
- Cement Industry (水泥工业): Kiln exhaust gas waste heat recovery for preheating air and feed material
- Steel Industry (钢铁工业): Blast furnace gas heat recovery, coke oven waste heat utilization
- Petrochemical Industry (石油化工): Furnace flue gas heat recovery, process stream heat integration
- Power Generation (发电): Boiler economizers, steam superheaters, condenser cooling coils
- Food & Pharmaceutical Processing: Steam generation from process waste heat, sanitary-grade heat exchangers
- Geothermal Energy: Downhole heat extraction coils for geothermal wellbore heat exchange
- Marine & Offshore: Exhaust gas waste heat recovery for ship propulsion systems
Performance in Waste Heat Recovery
Studies published in the field confirm that stress-free coiltube configurations achieve:
- Heat transfer coefficient improvement of 15–25% over conventional straight-tube arrangements
- Reduction in installation footprint by 60–80% compared to equivalent heat exchanger surface area in straight-tube design
- Service life extension of 3–5× over standard coiltube without stress-relief treatment
- Annual energy savings of 15–30% in integrated waste heat recovery systems
Quality Certifications
Applicable Standards
- ASTM A213: Standard Specification for Seamless Austenitic Stainless Steel Tube for High Temperature Service
- ASTM A269: Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and Similar Severities
- ASTM A312: Standard Specification for General Requirements for Heat Treatment of Stainless Steel Products
- ASTM A478: Standard Specification for General Requirements for Stainless Steel Bars and Shapes
- GB/T 12771: Stainless Steel Tubes for General Purposes
- GB/T 13296: Stainless Steel Tubes for Heat Exchangers and Heat Sinks
- EN 10216-5: Technical Delivery Conditions for Seamless Stainless Steel Tubes
- JIS G3459: Stainless Steel Tubes for General Use
Quality Management Certifications
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001:2015 — Environmental Management System Certification
- ISO 45001:2018 — Occupational Health and Safety Management System
- CE Marking — European Conformity for Pressure Equipment Directive (PED 2014/68/EU)
- EN 10204 3.1 — Third-Party Inspection Certificate (Material Test Certificate)
Inspection & Testing Protocols
- 100% Eddy Current Testing (ECT) per ASTM E309 — defect detection sensitivity ≥ 0.1 mm equivalent
- 100% Hydrostatic Pressure Testing per ASTM A530 — test pressure ≥ 1.5 × design pressure, hold time ≥ 30 seconds
- Lot-based Mechanical Testing per ASTM A370 — tensile, yield, and elongation verification
- Lot-based Chemical Analysis per ASTM E1086 — optical emission spectroscopy (OES) for full elemental verification
- Lot-based Microstructural Examination per ASTM E45 — grain size, phase distribution, and annealing quality assessment
- Residual Stress Measurement — X-ray diffraction sin²ψ method (ASTM E975) confirming < 30 MPa residual stress
- Intergranular Corrosion Testing — ASTM A262 Practice No. 1E (65% boiling acetic acid) for sensitization resistance verification
Unique Selling Points
- Zero Residual Stress: Industry-leading post-coiling stress-relief process eliminates the primary failure mechanism in conventional coiltubes, enabling reliable operation in demanding thermal cycling environments.
- Extended Service Life: Stress-free condition dramatically reduces susceptibility to Stress Corrosion Cracking (SCC), intergranular attack, and thermal fatigue — verified through accelerated aging tests demonstrating 3–5× life extension.
- Dimensional Stability: Maintains precise coil geometry throughout operational life, ensuring consistent heat transfer performance and eliminating maintenance requirements for coil re-tensioning or replacement.
- Compact High-Efficiency Design: Coiled configuration delivers maximum heat transfer surface area per unit volume, reducing system footprint and installation costs by up to 80%.
- Full Traceability: Each coil is accompanied by a complete material passport including chemical composition, mechanical properties, heat treatment records, NDT results, and residual stress measurement data.
- Custom Engineering: Flexible customization of coil diameter, tube dimensions, material grade, surface finish, and end treatment to meet specific application requirements.