Stainless Steel Coil Tube (Coiltube) for Once-Through Steam Generator Systems

Product Overview

The Stainless Steel Coil Tube (Coiltube), product reference No. 1187, is a precision-engineered coiled stainless steel tubing product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is specifically designed for use in once-through (direct-flow) steam generators, heat exchangers, and high-pressure thermal systems where compact heat transfer surface area and superior resistance to thermal cycling are critical requirements.

The coil tube configuration represents a significant advancement over traditional straight-tube designs in once-through steam generators. Through comparative design analysis, it has been demonstrated that coil tube geometries offer inherent advantages in terms of flow distribution uniformity, reduced residence time, enhanced convective heat transfer coefficients, and improved resistance to flow-induced vibration. The helical curvature introduces centrifugal forces that promote secondary flow patterns within the tube, effectively disrupting the thermal boundary layer and significantly increasing the overall heat transfer efficiency compared to straight-tube equivalents.

Material Composition & Physical Properties

The coil tubes are fabricated from high-grade austenitic stainless steel, with the following primary material grades available:

• SUS304 / AISI 304 (UNS S30400) — General-purpose corrosion-resistant grade with excellent formability, suitable for moderate-temperature steam generator applications up to 870°C.
• SUS316L / AISI 316L (UNS S31603) — Enhanced pitting and crevice corrosion resistance due to molybdenum addition; ideal for applications involving chloride-containing environments or high-purity steam.
• SUS321 / AISI 321 (UNS S32100) — Titanium-stabilized grade providing superior resistance to intergranular corrosion and thermal fatigue at elevated temperatures.
• SUS310S / AISI 310S (UNS S31008) — High-temperature grade for ultra-high-temperature service environments exceeding 1000°C.

Key Mechanical & Thermal Properties (SUS304 Reference)

• Tensile Strength: ≥ 520 MPa
• Yield Strength (0.2% offset): ≥ 205 MPa
• Elongation: ≥ 40%
• Thermal Conductivity: 16.3 W/(m·K) at 100°C
• Specific Heat Capacity: 0.50 J/(g·K) at 25°C
• Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /°C (20–100°C)
• Density: 7.93 g/cm³
• Maximum Service Temperature: 870°C (SUS304), 1093°C (SUS310S)

Technical Specifications

Parameter	Specification	Unit
Product Name	Stainless Steel Coil Tube (Coiltube)	—
Product Reference No.	1187	—
Tube Outer Diameter (OD)	6.0 / 8.0 / 10.0 / 12.7 / 14.0 / 19.0 (customizable)	mm
Tube Wall Thickness	0.5 / 0.8 / 1.0 / 1.2 / 1.5 / 2.0 (customizable)	mm
Coil Winding Diameter (Mean)	50 – 500	mm
Coil Pitch (Winding Spacing)	6 – 25	mm
Tube Length per Coil	10 – 50 (customizable)	m
Surface Finish	2B / BA (Bright Annealed) / Mirror Polish (Ra ≤ 0.1 μm)	—
Manufacturing Standard	ASTM A213 / ASTM A269 / GB/T 12771 / EN 10216-5	—
Pressure Rating	Up to 40 MPa (depending on dimensions)	MPa
Temperature Range	-196°C to 870°C (SUS304); up to 1093°C (SUS310S)	°C
Winding Tolerance	±0.5 mm (diameter), ±0.3 mm (pitch)	mm
Available Grades	SUS304, SUS304L, SUS316, SUS316L, SUS321, SUS310S	—

Manufacturing Process

The production of high-quality stainless steel coil tubes involves a multi-stage precision manufacturing process:

1. Raw Material Preparation: Cold-rolled stainless steel strip or seamless pipe stock is procured from certified mills and subjected to incoming inspection including spectroscopic analysis (PMI — Positive Material Identification) and mechanical property verification.
2. Pipe Forming & Welding: For welded tube variants, precision slitting, roll-forming, and continuous TIG (Tungsten Inert Gas) or automatic laser welding is performed with helium or argon internal shielding to maintain metallurgical integrity at the weld seam.
3. Coil Winding: The formed tube is wound onto a precision-controlled CNC coil winding machine. Critical process parameters include winding tension, pitch control, and diameter accuracy, all monitored in real time to ensure dimensional consistency within specified tolerances.
4. Heat Treatment / Solution Annealing: Post-forming annealing at 1050–1100°C followed by controlled cooling (air or water quench) to relieve residual stresses, restore austenitic microstructure, and maximize corrosion resistance.
5. Pickling & Passivation: Chemical cleaning to remove oxide scale and surface contaminants, followed by passivation treatment to restore the protective chromium oxide layer on the surface.
6. Surface Finishing: Optional mechanical polishing, electropolishing, or passivation to achieve required surface roughness (Ra) values for specific applications.
7. Quality Inspection & Testing: Comprehensive non-destructive testing (NDT) including eddy current testing, ultrasonic testing (UT), hydrostatic pressure testing, and dimensional verification.
8. Packaging & Shipping: Protected packaging with moisture barrier materials to prevent corrosion during transit and storage.

Design Advantages: Coil Tube vs. Straight Tube in Once-Through Steam Generators

Based on comparative design analysis of straight-tube and coil-tube configurations in once-through steam generators, the following performance advantages are attributed to the coil tube design:

• Enhanced Heat Transfer: The helical geometry induces Dean vortices (secondary flow), which continuously disrupt the thermal boundary layer, resulting in heat transfer coefficients 20–40% higher than equivalent straight tubes under identical flow conditions.
• Compact Design: The coil configuration achieves significantly higher heat transfer surface area per unit volume, enabling more compact steam generator designs with reduced footprint.
• Uniform Flow Distribution: The curvature promotes self-balancing of flow rates across parallel coil passages, reducing flow maldistribution issues common in straight-tube bundle designs.
• Reduced Thermal Stress: The inherent flexibility of the coil geometry accommodates differential thermal expansion, reducing thermal stress concentrations at tube-to-header junctions.
• Improved Resistance to Flow-Induced Vibration: The continuous curvature provides inherent structural damping, reducing susceptibility to flow-induced vibration (FIV) and fretting corrosion.
• Lower Pressure Drop Sensitivity: While the coil geometry introduces additional pressure drop due to curvature effects, the improved heat transfer per unit length allows for shorter tube runs, partially offsetting this penalty.

Applications

The Stainless Steel Coil Tube (Coiltube) is widely employed across multiple industrial sectors:

• Once-Through Steam Generators: Primary application for high-pressure and supercritical steam generation systems in power plants and industrial processes.
• Heat Exchangers & Recuperators: Compact coil-type heat exchangers for waste heat recovery, preheating, and condensation duties.
• Chemical Processing: Reactor coils, jacketed vessels, and process piping systems requiring corrosion-resistant, high-temperature containment.
• Oil & Gas Industry: Downhole heat exchangers, wellhead steam injection systems, and refinery process coils.
• Pharmaceutical & Food Processing: Sanitary-grade heating and cooling coils meeting FDA and GMP requirements.
• Nuclear Industry: Components for secondary circuit heat transfer systems (subject to nuclear-grade qualification).
• Aerospace & Defense: Lightweight heat exchange components for aircraft and spacecraft thermal management systems.
• Biomedical Equipment: Precision heating elements for medical devices and sterilization systems.

Quality Certifications & Standards Compliance

Wenzhou Jixing Metal Materials Co., Ltd maintains rigorous quality management systems and product certifications:

• ISO 9001:2015 — Quality Management System certification
• ISO 14001:2015 — Environmental Management System certification
• ISO 45001:2018 — Occupational Health & Safety Management System
• EN 10204 3.1 — Material test certificates conforming to European standards
• ASME — Section I (Power Boilers) and Section VIII (Pressure Vessels) compliance
• CE Marking — European Conformity for pressure equipment (PED 2014/68/EU)
• TÜV / DNV / Lloyd's Register — Third-party inspection and certification available upon request
• Mill Test Reports (MTR) — Full traceability documentation including chemical composition, mechanical properties, and NDT results

Unique Selling Points

1. Engineering-Validated Design: Product specifications are derived from rigorous comparative design studies of coil tube versus straight tube configurations in once-through steam generators, ensuring optimal performance parameters.

2. Precision Winding Tolerances: CNC-controlled winding ensures dimensional accuracy within ±0.5 mm diameter and ±0.3 mm pitch, critical for seamless integration into heat exchanger assemblies.

3. Full Material Traceability: Every coil tube batch is accompanied by complete mill test documentation enabling full material provenance tracking from raw material to finished product.

4. Customization Capability: Flexible manufacturing parameters accommodate bespoke specifications including tube dimensions, coil geometry, material grade, surface finish, and length configurations tailored to specific project requirements.

5. Comprehensive Testing Protocol: Multi-stage quality assurance including hydrostatic testing, eddy current inspection, dimensional verification, and surface integrity assessment ensures zero-defect delivery.

Ordering Information

For detailed quotations, custom specification development, or technical consultation regarding the Stainless Steel Coil Tube (Coiltube) product line, contact Wenzhou Jixing Metal Materials Co., Ltd directly. Technical support is available for system integration studies, thermal performance modeling, and material selection guidance for specific application scenarios.