Stainless Steel Spiral Coil Tube for Industrial Waste Heat Recovery Systems
Product Overview
The Stainless Steel Spiral Coil Tube (Product No. 799) is a precision-engineered coiled piping component manufactured by Wenzhou Jixing Metal Materials Co., Ltd, specifically designed for high-temperature waste heat recovery applications in the metallurgical and coking industries. This product category encompasses spiral coil tubes fabricated from austenitic and duplex stainless steel grades, engineered to withstand extreme thermal cycling, corrosive environments, and sustained mechanical loads. The coil tube configuration maximizes heat transfer surface area within a compact footprint, making it an optimal solution for integrated heat exchanger assemblies, particularly in salt bath spiral coil tube type coke oven ascending pipe waste heat recovery devices (盐浴螺旋盘管式焦炉上升管余热回收装置).
These coil tubes are supplied in coiled (盘管) form, enabling efficient storage, transportation, and on-site installation without the need for field welding of straight pipe sections. The continuous coil geometry ensures uniform thermal distribution and eliminates thermal stress concentrations at joints.
Material & Properties
The stainless steel spiral coil tubes are available in the following material grades, selected based on operating temperature, corrosive medium, and mechanical requirements:
- Austenitic Stainless Steels:
- 304 (UNS S30408 / 0Cr18Ni9): General-purpose grade with excellent corrosion resistance and formability; suitable for temperatures up to 870°C (1,598°F).
- 316 (UNS S31608 / 0Cr17Ni12Mo2): Enhanced resistance to pitting and crevice corrosion due to molybdenum addition; ideal for chloride-containing environments.
- 321 (UNS S32108 / 0Cr18Ni10Ti): Titanium-stabilized grade offering superior resistance to intergranular corrosion at elevated temperatures.
- 310S (UNS S31008 / 0Cr25Ni20): High-temperature grade with excellent oxidation resistance, suitable for sustained service up to 1,150°C (2,094°F).
- Duplex Stainless Steels:
- 2205 (UNS S31803): 22% Cr, 5% Ni, 3% Mo duplex grade providing high yield strength (≥450 MPa), excellent resistance to chloride stress corrosion cracking (SCC), and superior resistance to pitting corrosion.
- Heat-Resistant Alloys:
- 314 (UNS N08810 / 0Cr25Ni20): Ultra-high-temperature grade for sustained service up to 1,200°C (2,192°F) in oxidizing atmospheres.
Key Material Properties
| Property | 304 | 316 | 310S | 2205 Duplex |
|---|---|---|---|---|
| Chromium Content (%) | 18.0 – 20.0 | 16.0 – 18.0 | 24.0 – 26.0 | 22.0 – 23.0 |
| Nickel Content (%) | 8.0 – 10.5 | 10.0 – 14.0 | 19.0 – 22.0 | 4.5 – 6.5 |
| Molybdenum Content (%) | — | 2.0 – 3.0 | — | 2.5 – 3.5 |
| Maximum Continuous Service Temperature (°C) | 870 | 870 | 1,150 | 400 (long-term) / 350 (design) |
| Tensile Strength (MPa, minimum) | 515 | 485 | 515 | 550 |
| Yield Strength (MPa, minimum) | 205 | 170 | 205 | 450 |
| Elongation (%) | ≥40 | ≥40 | ≥40 | ≥15 |
| Thermal Expansion Coefficient (×10⁻⁶/K, 20–100°C) | 17.3 | 17.0 | 18.5 | 13.6 |
| Thermal Conductivity (W/m·K, 100°C) | 16.3 | 16.3 | 19.8 | 17.3 |
| Specific Heat (J/kg·K, 20°C) | 500 | 500 | 500 | 470 |
| Corrosion Potential (vs. SCE, mV) | −100 to +300 | −100 to +300 | −100 to +300 | −100 to +400 |
Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Product Name | Stainless Steel Spiral Coil Tube (盘管 / Coil Tube) | — |
| Product Code | 799 | — |
| Manufacturing Standard | ASTM A213 / ASTM A269 / GB/T 12771 / EN 10216-5 | ASTM, GB, EN |
| Tube Outer Diameter (OD) | Φ6 mm – Φ114.3 mm (1/4" – 4 1/2") | ASTM A213 |
| Tube Wall Thickness | 0.5 mm – 6.0 mm | ASTM A213 |
| Coil Bend Diameter | Φ50 mm – Φ2,000 mm (configurable) | Project-specific |
| Coil Length (per coil) | 5 m – 200 m (customizable) | — |
| Surface Finish | Bright Annealed (BA) / Pickled & Passivated / Brushed / Polished (2B, No.4, Mirror) | ASTM A478 / ASTM A480 |
| End Condition | Plain End / Beveled End / Threaded / Flanged (upon request) | ASME B1.20.1 / ASME B16.5 |
| Tolerance on OD | ±0.05 × wall thickness (or ±0.1 mm, whichever is greater) | ASTM A213 |
| Tolerance on Wall Thickness | ±10% of nominal | ASTM A213 |
| Welding Process | Continuous Welded (ERW) / Seamless / Argon Arc Welded (TIG/GTAW) | ASME B31.3 / EN 12164 |
| Heat Treatment | Solution Annealing (1050–1150°C) followed by controlled cooling | ASTM A213 / GB/T 12771 |
| Non-Destructive Testing (NDT) | Eddy Current Testing (ECT) / Ultrasonic Testing (UT) / Hydrostatic Testing / Penetrant Testing (PT) | ASTM E709 / ASTM E165 / ASME V |
| Maximum Operating Temperature | Up to 1,200°C (depending on grade) | Grade-dependent |
| Maximum Operating Pressure | Up to 25 MPa (depending on dimensions and grade) | ASME B31.3 |
| Corrosion Resistance | Excellent resistance to oxidizing acids, atmospheric corrosion, and chloride pitting (grade-dependent) | ASTM G48 / ASTM G150 |
| Packaging | Wooden reel / Steel reel with moisture-proof wrapping and export-grade labeling | ISO 4180 |
Manufacturing Process
The production of stainless steel spiral coil tubes at Wenzhou Jixing Metal Materials Co., Ltd follows a rigorous multi-stage manufacturing process to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection and Incoming Inspection:
- Hot-rolled stainless steel strip or coil is sourced from certified mills meeting ASTM, EN, or GB standards.
- Incoming materials undergo spectroscopic analysis (OES) for chemical composition verification, hardness testing, and visual surface inspection.
- Certification documents (Mill Test Certificates / MTC) are reviewed for conformity.
- Coil Slitting and Leveling:
- The master coil is slit to the required strip width using precision slitting lines with edge quality inspection.
- Strip is leveled through roller leveling mills to achieve flatness tolerance of ≤0.2% of strip width.
- Forming and Welding:
- Continuous forming machines roll the flat strip into a circular tube cross-section.
- For welded tubes, the seam is joined using Electric Resistance Welding (ERW) or Gas Tungsten Arc Welding (GTAW/TIG) with argon shielding to prevent oxidation.
- For seamless tubes, hot or cold piercing followed by multi-pass rolling is employed.
- Solution Annealing (Heat Treatment):
- Tubes are heated to 1,050–1,150°C in a protective atmosphere (reduced or vacuum) to dissolve carbides and restore full austenitic structure.
- Controlled cooling rate prevents sensitization and ensures uniform microstructure.
- For duplex grades, intercritical annealing at 1,050–1,100°C with rapid cooling maintains the austenite-ferrite balance (target: 40–60% ferrite).
- Pickling and Passivation:
- Acid pickling (HNO₃ + HF mixture or citric acid) removes mill scale, weld discoloration, and surface contamination.
- Passivation treatment with nitric acid or citric acid solution establishes a stable chromium oxide passive film for enhanced corrosion resistance.
- Post-passivation inspection includes blue dye test per ASTM A967.
- Coil Bending (Coiling):
- Finished straight tubes are fed through precision coiling machines to form the required spiral coil geometry.
- Bend radius is controlled to prevent wall thinning, ovalization, or wrinkling. Minimum bend radius is typically ≥3× OD for austenitic grades.
- Coil dimensions (bend diameter, number of turns, total length) are customized per project requirements.
- Quality Control and Non-Destructive Testing:
- Eddy Current Testing (ECT): Full-length inspection of weld seams and tube walls for discontinuities per ASTM E709.
- Hydrostatic Testing: Pressure testing at 1.5× design pressure to verify weld integrity and wall continuity.
- Dimensional Inspection: OD, wall thickness, coil diameter, and length verified using calipers, ultrasonic thickness gauges, and laser measurement systems.
- Visual and Surface Inspection: 100% visual examination for surface defects, scratches, and passivation quality.
- Spectroscopic Verification: PMI (Positive Material Identification) using XRF or OES to confirm grade identity.
- Packaging and Dispatch:
- Coils are wound onto export-grade wooden or steel reels with protective caps.
- Each coil is wrapped with moisture-proof plastic film and desiccant packs.
- Identification plates indicate product code, material grade, heat number, dimensions, and batch traceability information.
Applications
The stainless steel spiral coil tube is a versatile component deployed across multiple high-temperature industrial applications:
- Coke Oven Ascending Pipe Waste Heat Recovery (焦炉上升管余热回收):
- Primary application for the spiral coil tube configuration in salt bath heat recovery systems. The coil tube is immersed in a molten salt medium (typically KNO₃/NaNO₃ binary or ternary mixture) to recover waste heat from coke oven ascending pipe flue gas.
- The spiral coil design maximizes heat exchange surface area while maintaining structural integrity under thermal cycling between 400–900°C.
- Enables conversion of low-grade waste heat into usable thermal energy for steam generation, process heating, or power generation.
- Industrial Boiler and Fired Heater Tubing:
- Used as heat transfer elements in superheaters, economizers, air preheaters, and waste heat boilers in petrochemical, power generation, and steel manufacturing facilities.
- Chemical Process Heat Exchangers:
- Coil-type heat exchangers for corrosive chemical processing environments including sulfuric acid, hydrochloric acid, and organic solvent systems.
- Food and Pharmaceutical Industry:
- Sanitary coil heat exchangers for pasteurization, sterilization, and thermal processing of food and pharmaceutical products, manufactured in 304/316L with electropolished surfaces.
- Oil and Gas Industry:
- Subsea coil