Stainless Steel Coil Tube — Deep-Sea Manned Cabin Fan Coil System Application
Product Overview
The Stainless Steel Coil Tube (Product No. 434) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered coiled tubing product specifically designed for high-reliability thermal management applications in deep-sea manned cabin fan coil systems. These coil tubes serve as critical heat exchange components within the environmental control units of submersible pressure vessels, where they facilitate efficient heat transfer under extreme hydrostatic pressures, narrow temperature margins, and corrosive marine environments.
Unlike conventional straight-length stainless steel tubes, coil tubes are formed into continuous helical or serpentine geometries that maximize surface area-to-volume ratios within compact installation envelopes — a paramount requirement in space-constrained deep-sea cabin architectures.
Material & Properties
The coil tubes are fabricated from high-grade austenitic and duplex stainless steels selected for their exceptional combination of corrosion resistance, mechanical integrity, and thermal conductivity under deep-sea operating conditions.
- Base Grades: AISI 316L (UNS S31603), AISI 304L (UNS S30403), and Duplex 2205 (UNS S31803) are the primary alloy specifications employed.
- Corrosion Resistance: The molybdenum-enhanced 316L grade provides superior resistance to chloride-induced pitting and crevice corrosion in seawater-laden environments, with a Pitting Resistance Equivalent Number (PREN) of ≥25.
- Mechanical Properties: Yield strength of ≥205 MPa (304L) to ≥450 MPa (2205 Duplex); tensile strength of ≥515 MPa to ≥620 MPa depending on grade and cold-work condition.
- Thermal Conductivity: Approximately 14–16 W/(m·K) for austenitic grades, providing reliable heat transfer performance for fan coil thermal loops.
- Temperature Range: Serviceable from cryogenic temperatures (−196 °C) up to 870 °C, with no risk of brittle fracture in the cryogenic regime.
- Non-magnetic: Austenitic grades exhibit negligible magnetic permeability, critical for avoiding interference with sensitive navigation and instrumentation electronics within manned submersibles.
Specifications
| Parameter | Specification |
|---|---|
| Product Category | Coil Tube (盘管 / Coiltube) |
| Product Number | 434 |
| Outer Diameter (OD) | 6.0 mm – 50.8 mm (1/4" – 2" NPS equivalent) |
| Wall Thickness | 0.5 mm – 4.0 mm (customizable per application) |
| Coil Diameter | 100 mm – 2000 mm (tailored to system layout) |
| Tube Length per Coil | Up to 50 m continuous coil (single piece, no weld seams) |
| Material Grades | 304L, 316L, 321, 347H, Duplex 2205, Super Duplex 2507 |
| Surface Finish | Ra ≤ 0.4 μm (electropolished) or standard pickled & passivated |
| Pressure Rating | Up to 30 MPa (hydrostatic test per ASME B31.3 / EN 13480) |
| Manufacturing Standard | ASTM A269 / A270, EN 10217-7, GB/T 14976 |
| Delivery Condition | Cold-worked (CW) or Solution Annealed (SA) + Pickled & Passivated (PP) |
| End Preparation | Plain cut, beveled (37° ± 1°), or socket-weld ready |
| Traceability | Full mill certificate (EN 10204 3.1) with heat-number traceability |
Manufacturing Process
The production of deep-sea-grade stainless steel coil tubes follows a rigorous, multi-stage manufacturing protocol to ensure dimensional accuracy, metallurgical soundness, and performance integrity:
- Raw Material Selection & Inspection: Hot-rolled stainless steel strips or bars are sourced from certified mills with documented chemical composition (IEC 623 standard spectrographic analysis) and mechanical property verification.
- Piercing & Extrusion: Solid bar stock is heated to the austenitization temperature (1050–1150 °C) and pierced to form seamless tube blanks, eliminating the inherent weakness of welded seams.
- Pilger Rolling or Cold Drawing: The tube blanks undergo multi-pass cold reduction to achieve precise OD and wall thickness tolerances (±0.05 mm), with interpass annealing to prevent work-hardening failure.
- Solution Annealing: Tubes are heated to 1050–1100 °C and rapidly quenched in water or air to restore full austenitic structure, dissolve carbides, and maximize corrosion resistance.
- Coil Forming: The annealed tubes are fed through precision CNC-controlled forming dies to create the required helical or serpentine coil geometry. Forming is performed at controlled speeds to avoid ovality distortion and stress concentration.
- Pickling & Passivation: A two-stage chemical treatment removes mill scale and surface contaminants: pickling in nitric/hydrofluoric acid blend followed by passivation in dilute nitric acid to establish a protective chromium oxide film (≥100 nm thickness).
- Hydrostatic Testing: Each coil is pressure-tested at 1.5× the maximum design pressure per ASTM A269 requirements, with hold time of ≥30 seconds, ensuring zero permeation or leakage.
- Final Dimensional & NDT Inspection: Ultrasonic testing (UT) per ASTM E165 detects internal defects; eddy current testing (ECT) per ASTM E309 verifies surface integrity and wall thickness uniformity.
Applications
The deep-sea manned cabin fan coil system represents the primary application domain, but the product's versatility extends across multiple high-demand sectors:
- Deep-Sea Submersible Environmental Control: Integral heat exchange coils within fan coil units (FCUs) that regulate cabin temperature and humidity in manned submersibles operating at depths up to 10,000 m, where ambient pressure exceeds 100 MPa.
- Marine HVAC Systems: Offshore platform and subsea habitat ventilation and thermal regulation systems exposed to constant seawater spray and splash-zone corrosion.
- Submarine Life Support Systems: Compact thermal management loops for military and research submarine pressure hulls requiring non-magnetic, corrosion-free heat exchangers.
- Process Engineering: Chemical processing plants, pharmaceutical manufacturing, and food-grade applications requiring sanitary, corrosion-resistant coil assemblies.
- Energy Sector: Oil and gas production facilities, geothermal heat exchangers, and hydrogen storage thermal management systems.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality assurance framework ensuring full regulatory compliance for critical-subsurface applications:
- ISO 9001:2015 — Quality Management System certification covering all manufacturing, inspection, and traceability processes.
- ISO 3834-2 — Quality requirements for welding of metallic materials (applicable to any post-fabrication welding operations).
- EN 10204 Type 3.1 — Inspection certificate with independent test report traceability for every heat number.
- ASME B31.3 / B31.5 — Compliance with pressure piping code requirements for process and hydro/pneumatic piping systems.
- NACE MR0175 / ISO 15156 — Compliance with materials requirements for resistance to sulfide stress cracking in H₂S-containing environments.
- DNV-GL / ABS / LR — Classification society approval for marine and offshore applications.
- NSF/ANSI 61 — Drinking water system component safety certification (where applicable to food-grade or potable water systems).
Unique Selling Points
1. Seamless Single-Piece Coil Construction: The absence of longitudinal or circumferential weld seams eliminates the most common failure initiation sites in high-pressure thermal systems, significantly extending service life under cyclic thermal loading.
2. Deep-Sea Proven Design Heritage: Product specifications are derived from validated simulation models of manned submersible cabin fan coil systems, ensuring real-world performance in the most demanding thermal management environments.
3. Full Traceability & Digital Documentation: Every coil tube carries a unique identification code linked to a digital quality dossier containing mill certificates, dimensional reports, NDT results, and hydrostatic test records — enabling full lifecycle asset management.
4. Custom Geometric Engineering: CNC-driven coil forming allows bespoke helix pitch, coil diameter, and multi-turn configurations tailored to specific system layout constraints, reducing installation complexity and integration time.
5. Superior Corrosion Performance in Chloride Environments: The 316L and duplex alloy options deliver corrosion rates below 0.01 mm/year in seawater, exceeding the 20-year design life requirement for deep-sea equipment.