Stainless Steel Coil Tube (Coiltube) — Heat Screen Heat Exchanger Grade
1. Product Overview
Wenzhou Jixing Metal Materials Co., Ltd. (Product No. 1653) offers a precision-engineered Stainless Steel Coil Tube (盘管 / Coiltube), specifically designed for demanding thermal-fluid applications including heat screen heat exchangers (热屏换热器). A heat screen heat exchanger is a critical component in high-temperature environments—most notably in liquid rocket engine turbopump systems—where the coil tube serves as the primary heat-transfer element, protecting structural components from extreme thermal loads while simultaneously cooling the working fluid (typically liquid oxygen, liquid hydrogen, or liquid methane).
The coil tube is formed as a continuous helical winding from seamless stainless steel tubing, providing a high surface-area-to-volume ratio that maximizes convective and conductive heat exchange efficiency. The product is manufactured under strict metallurgical controls to ensure uniform wall thickness, dimensional accuracy, and reliable long-term performance under cyclic thermal and pressure loading conditions.
2. Material & Properties
2.1 Material Grades
The coil tube is available in the following austenitic stainless steel grades, selected based on the specific application requirements:
- SAE 304 / UNS S30408 — General-purpose corrosion-resistant alloy; suitable for moderate temperature and pressure environments.
- SAE 321 / UNS S32108 — Titanium-stabilized grade with superior resistance to intergranular corrosion; recommended for elevated-temperature service (up to 870 °C in reducing atmospheres).
- SAE 316L / UNS S31603 — Low-carbon molybdenum-bearing grade; provides enhanced resistance to pitting and crevice corrosion, ideal for cryogenic and chemical process applications.
- SAE 310S / UNS S31008 — High-temperature grade with excellent oxidation resistance; used in extreme thermal environments (up to 1150 °C continuous service).
2.2 Mechanical Properties (Annealed Condition, Typical)
| Property | SAE 304 | SAE 321 | SAE 316L | SAE 310S |
|---|---|---|---|---|
| Tensile Strength (MPa) | ≥ 520 | ≥ 520 | ≥ 485 | ≥ 515 |
| Yield Strength (0.2% Proof, MPa) | ≥ 205 | ≥ 205 | ≥ 170 | ≥ 205 |
| Elongation (%) | ≥ 40 | ≥ 40 | ≥ 45 | ≥ 35 |
| Hardness (HRB) | ≤ 92 | ≤ 92 | ≤ 92 | ≤ 92 |
| Density (g/cm³) | 8.00 | 8.00 | 8.03 | 8.00 |
| Thermal Conductivity at 100 °C (W/m·K) | 16.3 | 16.3 | 14.6 | 16.3 |
| Linear Expansion 20–100 °C (×10⁻⁶/K) | 17.3 | 17.3 | 17.8 | 18.5 |
2.3 Chemical Composition (wt%, Maximum unless noted)
| Element | SAE 304 | SAE 321 | SAE 316L | SAE 310S |
|---|---|---|---|---|
| C | 0.08 | 0.08 | 0.03 | 0.08 |
| Mn | 2.00 | 2.00 | 2.00 | 2.00 |
| P | 0.045 | 0.045 | 0.045 | 0.045 |
| S | 0.030 | 0.030 | 0.030 | 0.030 |
| Si | 1.00 | 1.00 | 1.00 | 0.75 |
| Cr | 18.00–20.00 | 17.00–19.00 | 16.00–18.00 | 24.00–26.00 |
| Ni | 8.00–10.50 | 9.00–12.00 | 10.00–14.00 | 19.00–22.00 |
| Ti | — | 5×C to 0.70 | — | — |
| Mo | — | — | 2.00–3.00 | — |
3. Specifications
3.1 Dimensional Specifications
| Parameter | Specification |
|---|---|
| Outer Diameter (OD) | Φ3.0 mm – Φ25.0 mm (customizable upon request) |
| Wall Thickness | 0.30 mm – 2.00 mm (tolerance ±0.05 mm) |
| Coil Pitch (Helical Spacing) | 1.5 mm – 15.0 mm (adjustable per design) |
| Coil Diameter (Mean) | Φ15 mm – Φ200 mm |
| Tube Length (Unwound) | 1 m – 12 m (continuous lengths available) |
| Coil Turns | 10 – 5,000+ (depending on application) |
| End Preparation | Flat cut, beveled, or threaded (per customer specification) |
| Surface Finish | Bright annealed, Ra ≤ 0.4 μm (polished available, Ra ≤ 0.1 μm) |
| Dimensional Tolerance (OD) | ±0.02 mm (precision grade) |
| Dimensional Tolerance (Coil Pitch) | ±0.05 mm |
3.2 Performance Parameters
| Parameter | Specification |
|---|---|
| Maximum Operating Pressure | Up to 25 MPa (design-dependent) |
| Operating Temperature Range | −196 °C (cryogenic) to +1,150 °C (continuous) |
| Heat Transfer Coefficient | 15,000 – 60,000 W/m²·K (fluid-dependent) |
| Flow Distribution Uniformity | ≥ 95% (verified via experimental flow distribution testing) |
| Pressure Drop (Typical) | 0.5 – 3.0 MPa (velocity and geometry dependent) |
| Thermal Cycling Endurance | ≥ 10,000 cycles (design life) |
4. Manufacturing Process
The production of precision stainless steel coil tubes for heat screen heat exchanger applications follows a rigorously controlled multi-stage manufacturing process:
- Raw Material Selection and Inspection — Seamless stainless steel tubes are sourced from certified mills (e.g., Outokumpu, POSCO, or domestic Grade-A producers). Incoming material undergoes spectroscopic analysis (OES), tensile testing, and hydrostatic pressure testing to verify compliance with ASTM A269, ASTM A213, or GB/T 12771 standards.
- Tube Straightening and Cutting — The raw tubing is cold-straightened using precision roller straighteners to eliminate residual curvature. It is then cut to the required length using a cold-cut saw to ensure square, burr-free ends.
- Coil Forming (Helical Winding) — A CNC-controlled coil forming machine winds the straight tube into the specified helical geometry. The forming process is executed under constant tension to prevent ovalization, kinking, or work-hardening of the tube wall. The coil pitch and mean diameter are continuously monitored via laser displacement sensors.
- Heat Treatment (Annealing and Stress Relief) — Following forming, the coil tube undergoes solution annealing at 1,050–1,150 °C followed by controlled cooling (air or water quench depending on grade). This process restores full austenitic microstructure, eliminates residual stresses introduced during forming, and ensures optimal corrosion resistance and mechanical properties. For SAE 321, a stabilization anneal at 870–900 °C is applied.
- Surface Cleaning and Passivation — The annealed coil is subjected to pickling (to remove oxide scale) and acid passivation (nitric acid or citric acid bath) to restore the passive chromium oxide layer, ensuring maximum corrosion resistance.
-
Dimensional Inspection and Non-Destructive Testing (NDT) — Each coil tube undergoes comprehensive quality verification including:
- OD and wall thickness measurement at multiple axial locations using ultrasonic thickness gauges
- Coil pitch and mean diameter verification via CMM (Coordinate Measuring Machine) or laser scanning
- Helium leak testing (per ASTM F2660) at 1.5× working pressure to detect micro-porosity or weld defects
- Visual inspection of surface finish and end preparation
- Flow Distribution Testing — For heat screen heat exchanger applications, a representative sample of coil tubes is subjected to flow distribution experiments (流量分配实验) in a dedicated test rig. The test rig simulates operating conditions (pressure, temperature, fluid properties) and measures the flow rate through each coil turn using Coriolis flow meters or differential pressure transducers. The objective is to verify that flow distribution uniformity meets or exceeds 95%, ensuring balanced heat exchange and preventing localized overheating.
- Final Packaging and Traceability — Each coil tube is individually packaged in moisture-proof packaging with a unique batch traceability tag. Full material certificates (MTC), test reports, and dimensional inspection records are provided with each shipment.
5. Applications
The stainless steel coil tube from Wenzhou Jixing Metal Materials Co., Ltd. is engineered for a wide range of high-performance thermal management applications:
- Liquid Rocket Engine Turbopump Heat Screen Heat Exchangers — The primary application domain. The coil tube functions as the heat screen element in turbopump housings, protecting pump bodies from the extreme thermal radiation of hot combustion gases (up to 2,500 °C) while simultaneously cooling the pressurized propellant (LOX, LH₂, or LCH₄). Flow distribution uniformity is critical to prevent hot spots and ensure engine reliability.
- Gas Turbine Engine Cooling Systems — Used in cooling coils for turbine blade cooling passages and combustor liner cooling in aviation and industrial gas turbines.
- Cryogenic Heat Exchangers — Employed in LNG (Liquefied Natural Gas) processing plants, cryogenic air separation units, and hydrogen liquefaction systems operating at temperatures as low as −269 °C.
- Nuclear Reactor Coolant Systems — Utilized in intermediate heat exchangers and steam generators in nuclear power plants (SAE 316L grade preferred for radiation resistance).
- Chemical Processing Heat Exchangers — Applied in aggressive chemical environments (acids, alkalis, chlorides) where corrosion resistance is paramount.
- Pharmaceutical and Food Industry Heat Exchangers — Hygienic-grade coil tubes (electropolished, Ra ≤ 0.1 μm) used in pasteurization, sterilization, and clean-in-place (CIP) systems.
- Aerospace and Defense Thermal Management — Regenerator coolers, radiator coils, and thermal control systems for spacecraft and high-altitude aircraft.
6. Quality Certifications and Standards
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and product certifications that ensure the highest level of reliability and compliance:
| Category | Standard / Certification | Description |
|---|---|---|
| Quality Management System | ISO 9001:2015 | Quality Management Systems — Requirements |
| Aerospace Quality | AS9100D | Quality Management Systems — Aerospace, Defense, and Space |
| Nuclear Quality | NQA-1 (Nuclear Quality Assurance) | U.S. Nuclear Regulatory Commission Quality Assurance Standards for Nuclear Power Plants |
| Material Standard (Tube) | ASTM A269 / ASTM A213 | Standard Specification for Seamless and |