Stainless Steel Spiral Coil Tube — Product No. 578
Product Overview
The Stainless Steel Spiral Coil Tube (Product No. 578), manufactured by Wenzhou Jixing Metal Materials Co., Ltd., is a precision-engineered coiled tubing product designed for high-efficiency thermal exchange applications. This product category falls under the classification of Coiltube (盘管), a versatile form of stainless steel tubing that is wound into continuous spiral configurations to maximize surface area within a compact volumetric footprint. The spiral geometry enables superior heat transfer performance, making it particularly suitable for applications in biogas digestion systems, industrial process heating, and thermal energy recovery.
Based on extensive experimental research into helical coil heat exchanger performance — as documented in studies such as the Experimental Study on Heat Transfer Performance of PEX Spiral Coil Tubes in Biogas Digesters — the design philosophy behind this product integrates optimized coil geometry, wall thickness tolerances, and material selection to achieve maximum thermal efficiency while maintaining structural integrity under cyclic thermal loading conditions.
Material & Properties
The coil tubes are fabricated from high-grade austenitic stainless steels, with the primary material options including:
- AISI 304 / UNS S30408 — General-purpose grade with excellent corrosion resistance and formability; the most widely specified grade for sanitary and process applications.
- AISI 316L / UNS S31603 — Enhanced corrosion resistance due to molybdenum (Mo) addition (2.0–3.0%); preferred for aggressive chemical environments, marine, and pharmaceutical applications.
- AISI 321 / UNS S32100 — Titanium-stabilized grade offering superior resistance to intergranular corrosion at elevated temperatures (up to 870°C).
- AISI 316Ti / UNS S31635 — Titanium-stabilized variant of 316L for high-temperature service with maintained pitting resistance.
Key material properties include:
- Maximum Service Temperature: 870°C (1600°F) for 304; 870°C for 316L
- Minimum Service Temperature: −196°C (−321°F) — no ductile-to-brittle transition
- Thermal Conductivity: 16.3 W/(m·K) at 20°C (304 grade)
- Specific Heat Capacity: 0.50 J/(g·K) at 20°C
- Density: 8.0 g/cm³
- Corrosion Resistance: Excellent resistance to atmospheric, chemical, and biological media including acetic acid, propionic acid, and hydrogen sulfide (H₂S) found in biogas environments
Specifications
| Parameter | Specification | Standard / Tolerance |
|---|---|---|
| Product No. | 578 | — |
| Product Name | Stainless Steel Spiral Coil Tube (Coiltube) | — |
| Material Grade | 304 / 304L / 316 / 316L / 321 / 316Ti | ASTM A269 / ASTM A213 / GB/T 12771 |
| Outer Diameter (OD) | 6 mm – 50.8 mm (1/4" – 2") | ±0.1 mm tolerance |
| Wall Thickness | 0.5 mm – 3.0 mm | ±10% of nominal |
| Coil Diameter (Center-to-Center) | 50 mm – 500 mm | ±1% of nominal |
| Coil Pitch (Spacing) | 15 mm – 80 mm | ±0.5 mm tolerance |
| Coil Length (Uncoiled) | Up to 100 m per coil (customizable) | — |
| Surface Finish | 2B / BA (Bright Annealed) / No. 4 Brushed / Electropolished (Ra ≤ 0.4 μm) | ASTM A480 |
| End Condition | Open end / Flanged / Threaded (BSP/NPT) / Welded closure | ASME B1.20.1 / B1.20.3 |
| Maximum Working Pressure | Up to 4.0 MPa (580 psi) | ASME B31.3 |
| Testing Standard | Hydrostatic testing at 1.5× working pressure | ASTM A269 / EN 10216 |
| Applicable Standards | ASTM A269, ASTM A213, GB/T 12771, EN 10216-5, JIS G3447 | — |
Manufacturing Process
The production of stainless steel spiral coil tubes follows a rigorous multi-stage manufacturing workflow designed to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection & Incoming Inspection: Cold-rolled stainless steel strip or seamless tubing is sourced from certified mill suppliers. Each batch undergoes spectroscopic analysis (OES — Optical Emission Spectroscopy) to verify chemical composition conformance to the specified grade.
- Coil Winding & Forming: The tube is fed through a precision coil-winding machine equipped with servo-controlled rollers that impose the desired coil diameter and pitch. The forming process is executed at controlled speeds to prevent work-hardening, ovalization, or micro-cracking of the tube wall. For cold-formed coils, the strain rate is maintained below the material's yield limit to preserve ductility.
- Heat Treatment (Annealing): Where required, the coiled tube assembly undergoes solution annealing at 1050–1100°C followed by controlled cooling to achieve a fully austenitic microstructure with optimal mechanical properties. This step is critical for eliminating residual stresses introduced during cold forming.
- Pickling & Passivation: The annealed coils are subjected to acid pickling (typically a mixed HNO₃/HF or HNO₃/HCl bath) to remove oxide scale, followed by passivation treatment to establish a chromium-rich passive film (≥ 10 nm thickness) that ensures long-term corrosion resistance.
- Surface Finishing: Depending on the application, coils receive additional surface treatments including mechanical brushing, electropolishing (using phosphoric acid electrolyte to achieve Ra ≤ 0.4 μm), or mirror polishing. Electropolished surfaces are particularly preferred for pharmaceutical, food-grade, and hygienic process applications.
- Dimensional Inspection & Quality Control: Each coil is inspected for coil diameter, pitch uniformity, tube OD, wall thickness, and straightness (residual springback). Non-destructive testing (NDT) methods including eddy current testing (ECT) and ultrasonic testing (UT) are employed to detect internal defects, wall thinning, or surface discontinuities.
- Hydrostatic Pressure Testing: All coils undergo hydrostatic testing at 1.5 times the maximum rated working pressure for a minimum dwell time of 60 seconds to verify leak-tightness and structural integrity.
- Packaging & Dispatch: Coils are protected with anti-corrosion wrapping (VCI — Vapor Corrosion Inhibitor film), wooden pallets, and moisture-absorbent desiccant packs for safe transit and storage.
Applications
The stainless steel spiral coil tube is a highly versatile component with applications spanning multiple industrial sectors:
- Biogas & Anaerobic Digestion Systems: Spiral coil heat exchangers are immersed within biogas digesters to maintain optimal fermentation temperature (35–40°C for mesophilic digestion). The helical geometry provides high heat transfer coefficients while minimizing the risk of biofilm fouling and blockage. Experimental studies have demonstrated that stainless steel coils outperform polymer alternatives (e.g., PEX — Cross-Linked Polyethylene) in long-term durability and thermal conductivity within the aggressive anaerobic environment containing H₂S, CO₂, and volatile fatty acids.
- Industrial Process Heating & Cooling: Used as immersion heaters or cooling coils in chemical reactors, mixing tanks, and heat recovery units. The high surface-area-to-volume ratio enables rapid thermal response and efficient energy utilization.
- Pharmaceutical & Food Processing: Electropolished coil tubes are employed in pasteurization systems, CIP (Clean-In-Place) loops, and sanitary fluid transfer lines where surface smoothness and corrosion resistance are critical.
- Geothermal & Solar Thermal Systems: Coil tubes serve as heat exchanger elements in closed-loop geothermal systems and concentrated solar power installations, leveraging stainless steel's resistance to scaling and thermal cycling fatigue.
- Automotive & Aerospace Thermal Management: Compact coil assemblies are used in oil coolers, fuel line routing, and thermal management loops where weight savings and high temperature tolerance are paramount.
- Marine & Offshore Engineering: 316L-grade coils are deployed in seawater cooling systems, ballast water treatment units, and subsea process piping due to their superior resistance to chloride-induced pitting and crevice corrosion.
- Building Services & HVAC: Spiral coils are integrated into air handling units, chiller systems, and underfloor radiant heating networks for efficient thermal distribution.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring compliance with international standards:
- ISO 9001:2015 — Quality Management Systems certification covering design, manufacturing, and post-sale service processes.
- ISO 14001:2015 — Environmental Management Systems certification demonstrating commitment to sustainable manufacturing practices.
- ISO 45001:2018 — Occupational Health and Safety Management Systems certification.
- EN 10204 3.1 — Material test certificates (MTC) issued by qualified third-party inspection bodies for each production lot.
- CE Marking — Conformity with European Directive 2014/68/EU (Pressure Equipment Directive — PED) for pressure-containing applications.
- NACE MR0175 / ISO 15156 — Compliance for sour service applications involving H₂S-containing environments.
- NSF/ANSI 61 — Drinking water system components certification (where applicable for food-grade and potable water applications).
- ASTM Certification — Product conformity to ASTM A269, ASTM A213, and ASTM A480 specifications with mill-test certification.
Unique Selling Points
1. Superior Thermal Performance: The optimized spiral geometry, validated through computational fluid dynamics (CFD) modeling and experimental heat transfer studies, delivers heat transfer coefficients (U-values) up to 2,500 W/(m²·K) — significantly outperforming straight-tube configurations by 40–60%.
2. Proven Durability in Aggressive Environments: Unlike polymer alternatives (e.g., PEX), stainless steel coils exhibit no degradation of mechanical or thermal properties over extended service life in anaerobic digesters, chemical reactors, and marine environments. Expected service life exceeds 20–25 years with proper maintenance.
3. Customizable Geometry: The manufacturing capability supports a wide range of coil diameters (50–500 mm), pitches (15–80 mm), tube sizes (6–50.8 mm OD), and end configurations, enabling precise engineering solutions tailored to specific vessel geometries and process requirements.
4. Hygienic Surface Quality: Electropolished finishes achieve surface roughness values (Ra) as low as 0.2–0.4 μm, meeting the most stringent sanitary requirements for pharmaceutical, biotechnology, and food-grade applications.
5. Comprehensive Traceability: Each coil is accompanied by full material traceability documentation including mill certificates, chemical analysis reports, mechanical test data, dimensional inspection records, and pressure test results — ensuring complete quality assurance from raw material to final delivery.