Stainless Steel Coil Tube for Industrial Heat Exchange Systems
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. | Product No.: 780
Product Overview
The Stainless Steel Coil Tube is a precision-engineered coiled piping product designed for demanding industrial heat exchange applications, particularly in ammonia processing systems, cryogenic evaporators, and chemical processing facilities. Unlike straight seamless tubes, coil tubes are manufactured in continuous helical or spiral configurations that maximize heat transfer surface area within confined spatial envelopes. This product line addresses the critical engineering challenge of maintaining fluid flow integrity in evaporator assemblies where blockage, fouling, and corrosion represent significant operational hazards.
Wenzhou Jixing Metal Materials Co., Ltd. specializes in the design, manufacturing, and supply of stainless steel coil tubes that meet the stringent requirements of process industries. The coil geometry provides superior thermal performance, reduced pressure drop, and enhanced resistance to thermal cycling compared to conventional straight-tube heat exchanger designs.
Material & Properties
Base Material Grades
Coil tubes are fabricated from high-grade austenitic stainless steel, selected for exceptional corrosion resistance, mechanical strength, and thermal stability across a wide operating temperature range. The primary material grades include:
- SUS 304 / ASTM A213 TP304: General-purpose austenitic stainless steel with excellent resistance to atmospheric and chemical corrosion. Suitable for ammonia service environments.
- SUS 316 / ASTM A213 TP316: Molybdenum-enhanced grade offering superior resistance to pitting and crevice corrosion, particularly in chloride-containing environments.
- SUS 316L / ASTM A213 TP316L: Low-carbon variant designed for welding applications and cryogenic service, minimizing intergranular corrosion risk.
- SUS 321 / ASTM A213 TP321: Titanium-stabilized grade providing excellent resistance to high-temperature scaling and stress corrosion cracking.
Mechanical Properties
| Property | SUS 304 | SUS 316 | SUS 316L |
|---|---|---|---|
| Tensile Strength (MPa) | ≥ 515 | ≥ 515 | ≥ 485 |
| Yield Strength (MPa) | ≥ 205 | ≥ 205 | ≥ 170 |
| Elongation (%) | ≥ 40 | ≥ 40 | ≥ 45 |
| Density (g/cm³) | 8.00 | 8.03 | 8.03 |
| Thermal Conductivity (W/m·K, 20°C) | 16.3 | 14.6 | 14.6 |
| Operating Temperature Range (°C) | -196 to +870 | -196 to +870 | -273 to +870 |
Chemical Composition
| Element | C (%) | Cr (%) | Ni (%) | Mo (%) | Si (%) | Mn (%) |
|---|---|---|---|---|---|---|
| SUS 304 | ≤ 0.08 | 18.0–20.0 | 8.0–10.5 | — | ≤ 1.00 | ≤ 2.00 |
| SUS 316 | ≤ 0.08 | 16.0–18.0 | 10.0–14.0 | 2.00–3.00 | ≤ 1.00 | ≤ 2.00 |
| SUS 316L | ≤ 0.03 | 16.0–18.0 | 10.0–14.0 | 2.00–3.00 | ≤ 1.00 | ≤ 2.00 |
Specifications
| Parameter | Specification |
|---|---|
| Product Type | Stainless Steel Coil Tube (Helical/Spiral Coil) |
| Outer Diameter Range (OD) | Φ 6 mm – Φ 108 mm (customizable) |
| Wall Thickness Range | 0.3 mm – 6.0 mm |
| Coil Diameter | 100 mm – 2000 mm (as required) |
| Coil Length per Spool | Up to 1000 m (continuous) |
| Helix Pitch | 15 mm – 100 mm (adjustable) |
| End Connection Type | Butt-weld, Threaded (NPT/BSP), Flanged, or U-bend |
| Surface Finish | Baught (2B), No. 4 Brushed, Mirror (Ra ≤ 0.4 μm), Pickled & Passivated |
| Manufacturing Standard | ASTM A213 / ASME SA-213 / EN 10216-5 / GB/T 14976 |
| Coil Forming Standard | ASTM A381 / ASME SA-381 |
| Maximum Operating Pressure | Up to 40 bar (pressure-rated per ASME Section VIII) |
| Inspection Standard | ASTM A999 / ASTM A376 (Eddy Current Testing) |
| Packaging | Wooden crate or export-grade steel frame with desiccant protection |
Manufacturing Process
The production of stainless steel coil tubes at Wenzhou Jixing Metal Materials Co., Ltd. follows a rigorous multi-stage process ensuring dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection: Certified stainless steel seamless tubes (or welded tubes for larger diameters) are procured from accredited mills. Incoming material undergoes chemical composition verification via Optical Emission Spectrometry (OES) and mechanical property testing including tensile and hardness testing.
- Tube Straightening & Annealing: Raw tubes are straightened using a multi-roller straightening machine and subjected to solution annealing at 1050°C–1150°C followed by controlled cooling to restore full austenitic microstructure and relieve residual stresses.
- Coil Forming (Helical Winding): Tubes are wound into the required helical or spiral geometry using a CNC-controlled coil forming machine. The winding parameters—helix diameter, pitch, and number of turns—are precisely controlled to meet design specifications. Cold forming is employed for smaller diameters; warm forming is used for thicker wall sections to prevent work hardening.
- Stress Relief Annealing: Post-forming annealing is performed to eliminate residual stresses introduced during the coiling process, ensuring dimensional stability during subsequent welding and service.
- Welding & End Preparation: Coil ends are prepared for connection via TIG (Tungsten Inert Gas) welding with argon gas shielding to prevent oxidation. Butt-weld joints are performed in accordance with ASME Section IX qualification procedures. Threaded connections are machined using precision tapping operations.
- Surface Treatment: Tubes undergo pickling and passivation treatment using nitric acid-citric acid blend to remove mill scale and form a protective chromium oxide layer. Mirror polishing is available for applications requiring hygienic or aesthetic finishes.
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Quality Inspection: Every batch undergoes comprehensive inspection including:
- Dimensional verification (OD, wall thickness, coil diameter, pitch)
- Visual inspection for surface defects and geometric irregularities
- Eddy current testing (ECT) per ASTM A376 for internal flaw detection
- Hydrostatic pressure testing at 1.5× design pressure
- Positive Material Identification (PMI) via XRF analysis
- Packaging & Dispatch: Completed coil tubes are wrapped in protective film, placed in export-grade wooden crates with desiccant packs, and labeled with material traceability documentation.
Applications
Stainless steel coil tubes are employed across a broad spectrum of industrial sectors where efficient heat transfer, corrosion resistance, and spatial efficiency are critical:
Primary Applications
- Ammonia Evaporator Systems: Liquid ammonia evaporator coil tubes serve as the primary heat transfer element in refrigeration and ammonia processing plants. The coil geometry maximizes heat exchange surface area while minimizing the footprint of evaporator vessels. Special attention is given to preventing blockage caused by ammonia decomposition products and moisture accumulation.
- Chemical Processing: Heat exchangers, reactors, and condensers in petrochemical, pharmaceutical, and specialty chemical manufacturing. Stainless steel coil tubes resist aggressive chemical media including acids, alkalis, and organic solvents.
- Cryogenic Systems: Liquefied Natural Gas (LNG) processing, liquid nitrogen/oxygen equipment, and cryogenic storage where SUS 316L coil tubes maintain ductility at temperatures as low as -196°C.
- Power Generation: Superheater tubes, economizers, and condensers in thermal power plants and cogeneration systems.
- Food & Beverage Processing: Pasteurizers, sterilizers, and heat exchangers in dairy, brewing, and pharmaceutical manufacturing where sanitary-grade mirror-finish coil tubes are required.
- Marine & Offshore: Seawater heat exchangers, ballast water systems, and offshore platform cooling circuits requiring resistance to saltwater corrosion.
- HVAC & Refrigeration: Evaporator and condenser coils in industrial air conditioning, cold storage facilities, and process refrigeration systems.
Ammonia Evaporator Coil Tube — Special Considerations
Based on industry experience documented in operational learning materials regarding ammonia area liquid ammonia evaporator coil tube blockage, the following engineering considerations are critical for ammonia service applications:
- Blockage Prevention: Coil tube internal diameters must be designed to accommodate the flow velocity requirements of liquid ammonia, preventing sediment accumulation. Minimum internal diameter of Φ 12 mm is recommended for liquid ammonia service to maintain adequate flow velocity and prevent blockage.
- Moisture Control: Ammonia systems are highly sensitive to moisture contamination. Coil tubes must be thoroughly dried and purged with nitrogen prior to commissioning. Internal surface finish of Ra ≤ 0.8 μm is recommended to minimize fouling.
- Material Compatibility: Stainless steel coil tubes (SUS 304/316) are compatible with anhydrous ammonia. However, copper alloys must be strictly excluded from ammonia systems due to the risk of catastrophic failure from ammonia-copper reactions.
- Thermal Cycling Resistance: Ammonia evaporator coil tubes experience frequent thermal cycling between refrigeration and defrost cycles. The selected stainless steel grades maintain mechanical integrity under repeated thermal stress.
- Inspection & Maintenance Access: Coil tube configurations should allow for periodic inspection and flushing. U-bend configurations with accessible ports are recommended for ammonia evaporator applications.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and product certification framework:
Management System Certifications
- ISO 9001:2015 — Quality Management System
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health & Safety Management System
Product & Industry Certifications
- ASME "S" Stamp — Pressure Vessel and Piping Components
- TÜV Rheinland — Product Conformity Assessment
- CE Marking — European Conformity (PED 2014/68/EU)
- API Monogram — American Petroleum Institute (where applicable)
- EN 10204 3.1 — Material Test Certificate (Third-Party