Stainless Steel Coil Tube for Primary Steam Heating Systems
Product Overview
The Stainless Steel Coil Tube (Model No. 321) is a precision-engineered coiled tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is specifically designed for use in primary steam heating systems (一次蒸汽加热盘管系统), where it functions as the core heat exchange element facilitating thermal energy transfer between superheated steam and the process medium. The coil tube is fabricated from high-grade austenitic stainless steel, exhibiting exceptional resistance to thermal cycling, corrosion, and mechanical fatigue under sustained high-temperature and high-pressure operating conditions.
This product represents an optimized design iteration informed by systematic engineering analysis of primary steam heating coil tube system performance, incorporating improvements in coil geometry, material selection, and manufacturing tolerances to maximize heat transfer efficiency while minimizing pressure drop and thermal stress accumulation.
Material & Properties
Base Material
The coil tube is manufactured from austenitic stainless steel conforming to international standards including ASTM A213, EN 10216-5, and GB/T 14976. The primary grades utilized include:
- 321 (UNS S32100) — Titanium-stabilized austenitic stainless steel, offering superior resistance to intergranular corrosion (IGC) at elevated temperatures
- 304 (UNS S30400) — General-purpose austenitic grade for moderate-temperature applications
- 316 (UNS S31600) — Molybdenum-enhanced grade for aggressive chemical environments
Key Mechanical & Physical Properties
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (UTS) | ≥ 515 MPa | ASTM A213 / EN 10216-5 |
| Yield Strength (0.2% Proof) | ≥ 205 MPa | ASTM A213 |
| Elongation | ≥ 35% | ASTM A213 |
| Operating Temperature Range | -40 °C to +650 °C | Manufacturer's data |
| Maximum Design Pressure | ≤ 16.0 MPa (adjustable per specification) | ASME VIII Div.1 |
| Thermal Conductivity (at 100 °C) | 16.3 W/(m·K) | ASTM E1461 |
| Corrosion Resistance | Excellent against intergranular corrosion; resistant to pitting in chloride environments (316 grade) | ASTM A262 Practice E |
| Cyclic Fatigue Endurance | ≥ 10,000 thermal cycles (verified under design conditions) | Manufacturer's testing protocol |
Specifications
| Parameter | Specification | Notes |
|---|---|---|
| Product Designation | Coil Tube — Model 321 | Primary steam heating application |
| Outer Diameter (OD) | 12.7 mm / 19.0 mm / 25.4 mm / 33.7 mm (customizable) | Tolerance: ±0.15 mm |
| Wall Thickness | 1.5 mm – 3.0 mm (standard); up to 5.0 mm (on request) | Tolerance: ±10% of nominal |
| Coil Bending Diameter | ≥ 5D (five times the tube OD) | Ensures minimum strain during cold bending |
| Coil Pitch (Center-to-Center Spacing) | 25 mm – 50 mm (configurable per heat duty) | Optimized for turbulence and ΔP balance |
| Tube Length per Coil | 5 m – 50 m (standard); up to 120 m (special order) | Continuous coil; no butt welds in coil body |
| Surface Finish | Mill finish (Ra ≤ 1.6 μm); polished finish available (Ra ≤ 0.4 μm) | ASTM A269 / EN 10217 |
| End Preparation | Plain cut, beveled, or threaded (BSPP / NPT) | Per customer drawing |
| Heat Treatment | Solution annealed at 1040–1120 °C, water quenched | Followed by stress-relief anneal at 425 °C (321 grade) |
| Delivery Condition | Coiled, bundled with protective end caps and moisture-absorbing desiccant | ISO 11607 packaging compliance |
Manufacturing Process
The production of the Model 321 stainless steel coil tube follows a rigorously controlled multi-stage manufacturing sequence designed to ensure dimensional accuracy, metallurgical integrity, and long-term operational reliability:
- Raw Material Procurement & Inspection — Certifying-quality austenitic stainless steel seamless tubes are sourced from accredited mills. Each batch undergoes spectrographic chemical analysis (ASTM E415) and ultrasonic internal defect inspection (ASTM A777) prior to acceptance.
- Dimensional Verification & Straightening — Incoming tubes are inspected for OD, wall thickness, and straightness using laser measurement systems. Any deviation beyond tolerance triggers rejection or corrective rework.
- Cold Bending & Coiling — Tubes are cold-bent into the specified coil geometry using hydraulic mandrel bending machines with CNC-controlled bend radii. The minimum bend radius is maintained at ≥ 5D to prevent wall thinning and ovality exceeding 5% of nominal OD.
- Solution Annealing — Coiled tubes undergo solution heat treatment in a continuous annealing furnace at 1040–1120 °C followed by rapid water quenching. For 321 grade, a subsequent stress-relief anneal at 425 °C is performed to optimize titanium carbide precipitation and suppress sensitization.
- Surface Finishing — Tubes receive electropolishing or mechanical polishing as specified. Electropolishing removes up to 10–25 μm of surface material, reducing surface roughness to Ra ≤ 0.4 μm and enhancing corrosion resistance.
- Pressure Testing & Non-Destructive Examination (NDE) — Each coil is hydrostatically pressure-tested at 1.5× the maximum design pressure (ASME BPV Section I). Ultrasonic and eddy current testing verify the absence of internal and surface defects.
- Final Inspection & Documentation — A comprehensive inspection report is compiled, including material test reports (MTR), dimensional certificates, NDE results, pressure test records, and traceability documentation conforming to ISO 9001:2015 quality management requirements.
Applications
The Model 321 stainless steel coil tube is engineered for demanding thermal processing applications where reliable heat transfer and long service life are critical:
- Primary Steam Heating Systems (一次蒸汽加热盘管系统) — Core heat exchange element in high-pressure steam heating loops for industrial process heating, where the coil tube transfers thermal energy from superheated steam to the target process fluid.
- Chemical & Petrochemical Processing — Reactor jacket heating, reboilers, and heat exchangers in environments requiring resistance to corrosive chemicals and high-temperature steam.
- Food & Pharmaceutical Processing — Steam sterilization (SIP/CIP) systems, pasteurization units, and sanitary heat exchangers where hygienic surface finish and corrosion resistance are mandatory.
- Power Generation & Cogeneration — Feedwater preheating, condenser coil tubes, and steam recovery systems in combined heat and power (CHP) plants.
- Pulp & Paper Industry — Steam heating coils for dryer cylinders, digesters, and evaporator systems exposed to acidic and alkaline process fluids.
- Textile & Dyeing Industry — Dyeing machine heating coils and hot air circulation systems requiring sustained high-temperature steam exposure.
Unique Selling Points
- Optimized Coil Geometry for Enhanced Heat Transfer — The coil pitch and bending diameter are computationally optimized to maximize turbulent flow within the tube while minimizing pressure drop, resulting in a 15–25% improvement in heat transfer coefficient compared to conventional coil designs.
- Titanium-Stabilized 321 Grade Availability — The use of UNS S32100 titanium-stabilized stainless steel provides superior resistance to intergranular corrosion during prolonged exposure to temperatures in the sensitization range (425–870 °C), extending service life in high-temperature steam environments.
- Seamless Continuous Coil Construction — Elimination of butt welds within the coil body eliminates potential failure points and ensures uniform hydraulic and thermal performance throughout the entire coil length.
- Full Traceability & Quality Documentation — Every coil is delivered with complete material traceability documentation, including mill certificates, heat numbers, and NDE reports, ensuring compliance with ASME, PED, and ISO standards.
- Customizable Specifications — Wenzhou Jixing Metal Materials Co., Ltd. offers fully customizable coil dimensions, wall thicknesses, and surface finishes to match specific system design requirements and operating conditions.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and holds the following certifications and complies with the following standards:
| Certification / Standard | Scope of Compliance |
|---|---|
| ISO 9001:2015 | Quality Management System — covers design, manufacturing, and supply of stainless steel coil tubes |
| ISO 14001:2015 | Environmental Management System — environmentally responsible manufacturing processes |
| ASME BPV Section I | Pressure Vessel and Boiler Code compliance for pressure-containing coil tube assemblies |
| EU PED 2014/68/EU | Pressure Equipment Directive compliance for equipment intended for use within the European Economic Area |
| CE Marking | Conformity with applicable EU health, safety, and environmental protection requirements |
| EN 10204-3.1 | Inspection documents — full material test reports with independent third-party verification |
| ASTM A213 | Standard specification for seamless austenitic stainless steel boiler, heat exchanger, and heater tubes |
| GB/T 14976 | Chinese national standard for seamless stainless steel tubes for general applications |
Note: All product specifications described herein are subject to verification against the latest applicable edition of the referenced standards. Custom specifications and deviations from standard dimensions should be confirmed through written agreement between the manufacturer and the purchaser prior to production commencement. Wenzhou Jixing Metal Materials Co., Ltd. reserves the right to update product specifications as new engineering data and material technology become available.