Large Diameter Flexible Stainless Steel Coil Tube — Technical Specification
Product Code: No. 258 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. (温州吉兴金属材料有限公司) | Category: Literature Learning & Process Engineering Documentation
1. Product Overview
The Large Diameter Flexible Stainless Steel Coil Tube (大直径柔性盘管) is a precision-engineered tubular component formed by cold-drawing and coiling high-grade austenitic stainless steel wire into a helical spring-like structure. Unlike conventional rigid piping, the flexible coil tube is designed to absorb thermal expansion, dampen mechanical vibration, and accommodate misalignment within complex industrial systems. The product is distinguished by its large outer diameter, high spring rate, and superior fatigue resistance, making it indispensable in high-pressure, high-temperature, and dynamically loaded environments.
This specification document is derived from the technical research study titled "Research on Assembly Process Method Technology for Large Diameter Flexible Coil Tubes" (《大直径柔性盘管套装工艺方法技术研究》), which systematically investigates the forming, assembly, and installation methodologies required to achieve consistent performance and dimensional accuracy in large-diameter coil tube configurations.
2. Material & Properties
2.1 Base Material Grades
- SAE 304 / AISI 304 (UNS S30400): General-purpose austenitic stainless steel with 18% Chromium (Cr) and 8% Nickel (Ni). Offers excellent corrosion resistance, formability, and weldability in non-aggressive environments.
- SAE 316 / AISI 316 (UNS S31600): Molybdenum-bearing (2–3% Mo) austenitic grade providing enhanced resistance to pitting and crevice corrosion in chloride-containing media.
- SAE 316L (UNS S31603): Low-carbon variant of 316 with C ≤ 0.03%, optimized for welding applications and resistance to intergranular corrosion.
- SAE 321 / AISI 321 (UNS S32100): Titanium-stabilized (Ti ≥ 5×C) austenitic grade suitable for sustained service temperatures up to 870 °C.
- SAE 304L (UNS S30403): Low-carbon variant with C ≤ 0.03%, preferred for heavy welding and cryogenic applications.
2.2 Mechanical Properties (Typical — Annealed Condition)
| Property | 304 / 304L | 316 / 316L | 321 | Test Standard |
|---|---|---|---|---|
| Tensile Strength (UTS) | ≥ 515 MPa | ≥ 515 MPa | ≥ 515 MPa | ASTM A270 / EN 10217-7 |
| 0.2% Proof Stress (Yield Strength) | ≥ 205 MPa | ≥ 205 MPa | ≥ 205 MPa | ASTM A270 |
| Elongation (in 50 mm gauge) | ≥ 40% | ≥ 40% | ≥ 40% | ASTM E8 |
| Hardness (HBW) | ≤ 217 | ≤ 217 | ≤ 217 | ASTM E10 |
| Spring Rate (Cold-Set) | Customizable | Customizable | Customizable | ASTM A922 |
| Maximum Service Temperature | 870 °C | 870 °C | 870 °C | — |
| Minimum Service Temperature | −196 °C | −196 °C | −196 °C | — |
2.3 Key Metallurgical Characteristics
- Austenitic Microstructure (FCC): Non-magnetic in the annealed condition, ensuring suitability for electromagnetic-sensitive applications.
- Work Hardening Capability: The cold-coiling process induces controlled strain hardening, enhancing spring rate and load-bearing capacity without compromising ductility.
- Cyclic Fatigue Resistance: The coiled geometry distributes stress uniformly, enabling millions of load cycles before failure under proper design conditions.
3. Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Coil Outer Diameter (OD) | 50 mm – 500 mm (customizable) | Manufacturer's design specification |
| Wire Diameter (Wire Dia.) | 1.5 mm – 25 mm | ASTM A270 / EN 10217-7 |
| Number of Active Coils | 2 – 50+ (design-dependent) | ASTM A922 |
| Free Length (FL) | 50 mm – 2000 mm (customizable) | — |
| Working Length (WL) | 70% – 85% of FL | ASTM A922 |
| Coil Pitch / Spacing | 0 mm (closed) to 10 mm (open) | Design specification |
| End Configuration | Plain, Ground, Peened, or Closed & Ground | ASTM A922 |
| Surface Finish | Ra ≤ 0.4 μm (polished) / Ra ≤ 1.6 μm (passivated) | ASTM A967 / ASTM A968 |
| Spring Rate Tolerance | ± 6% (standard) / ± 3% (precision) | ASTM A922 |
| Dimensional Tolerance (OD) | ± 1.5% (standard) / ± 0.5% (precision) | ISO 1219 |
| Dimensional Tolerance (FL) | ± 2.5% (standard) / ± 1.0% (precision) | ISO 1219 |
| Corrosion Resistance | ASTM A967 (acid pickling) / ASTM A968 (passivation) | ASTM A967 / ASTM A968 |
| Heat Treatment | Solution Annealing (1010–1150 °C) + Water Quench | ASTM A270 |
| Maximum Working Stress | ≤ 0.45 × UTS (design limit) | ASME BPV Section II |
| Design Life | ≥ 10⁷ load cycles (fatigue) | ASTM A922 |
4. Manufacturing Process
The production of large diameter flexible coil tubes involves a multi-stage process chain, each step critically controlled to ensure dimensional accuracy, mechanical integrity, and surface quality. The following process flow reflects the methodology documented in the referenced research study.
4.1 Process Flow Diagram
- Raw Material Inspection & Certification: Incoming stainless steel wire is verified against mill certificates (MTC), including chemical composition analysis (ICP-OES), mechanical property testing, and visual surface inspection.
- Wire Annealing & Straightening: Cold-drawn wire is solution-annealed at 1010–1150 °C followed by water quenching to restore full austenitic ductility. The wire is then straightened and decoppered to remove drawing lubricants.
- Wire Coating / Lubrication: A controlled layer of drawing compound or polymer coating is applied to reduce friction during the coiling operation and prevent galling.
- Computer-Numerical-Control (CNC) Coiling: The wire is fed through a precision CNC coiling machine equipped with servo-controlled mandrels and guides. The coil geometry (OD, pitch, number of turns, wire diameter) is programmed to achieve the target spring rate and free length. The coiling process is executed under constant tension to ensure uniform inter-coil spacing.
- End Forming & Grinding: Coil ends are formed to the specified configuration (plain, ground, peened, or closed-and-ground) using automated end-grinding stations. Ground ends ensure flat load-bearing surfaces and uniform stress distribution.
- Cold Setting (if applicable): For applications requiring a higher spring rate, the coil is compressed to its solid height and held for a controlled duration, inducing permanent strain hardening in the wire.
- Stress Relief / Tempering: The coil is subjected to a low-temperature stress relief cycle (typically 400–500 °C for austenitic grades) to stabilize dimensions and reduce residual stresses from cold setting.
- Surface Treatment — Pickling & Passivation: The finished coil is acid-pickled (ASTM A967) to remove scale and discoloration, followed by passivation (ASTM A968) using nitric or citric acid solutions to restore the protective chromium oxide film.
- Final Dimensional & Mechanical Inspection: Each coil undergoes full dimensional verification (OD, FL, pitch, wire diameter) using coordinate measuring machines (CMM) or laser scanning systems. Spring rate is verified on a calibrated load-deflection testing machine.
- Packaging & Shipment: Conforming coils are individually packaged in protective wrapping, labeled with traceability identifiers, and shipped according to the customer's delivery schedule.
4.2 Assembly Process Methodology (Key Research Findings)
The referenced study specifically addresses the assembly and installation process technology for large-diameter flexible coil tubes, identifying the following critical process parameters:
- Pre-Assembly Stress Analysis: Finite Element Analysis (FEA) is performed on the assembled coil tube configuration to predict stress concentrations at coil-to-coil contact points, end-seat interfaces, and load application zones.
- Sequential Coil Stacking Protocol: For multi-coil assemblies, coils are stacked and secured using precision-machined spacers and retainer plates. The stacking sequence is optimized to ensure uniform load distribution and prevent differential compression.
- Inter-Coil Gap Calibration: The gap between adjacent coils in a stacked assembly is precisely calibrated to maintain the designed spring rate and prevent coil binding during dynamic loading.
- Load Path Verification: The assembly is tested under representative operating loads to verify that the load path is symmetric and that no individual coil is overloaded beyond its design capacity.
- Thermal Expansion Compensation: The assembly design incorporates allowances for differential thermal expansion between the coil tube material and surrounding structural components.
5. Applications
Large diameter flexible stainless steel coil tubes find extensive application across multiple industrial sectors where vibration isolation, thermal expansion absorption, and dynamic load management are critical:
5.1 Power Generation
- Steam turbine exhaust and inlet piping vibration dampening
- Boiler feedwater line thermal expansion compensation
- Generator mounting and anti-vibration isolation
- Nuclear reactor containment piping isolation systems
5.2 Petrochemical & Oil/Gas
- Refinery distillation column support and isolation
- Offshore platform piping vibration control
- Compressor and pump anti-vibration mounts
- High-pressure flare system thermal expansion joints
5.3 Aerospace & Defense
- Jet engine exhaust system vibration isolation
- Aircraft landing gear shock absorption components
- Missile and rocket structural load management
- Cryogenic fuel tank thermal expansion compensation
5.4 Automotive & Transportation
- Exhaust system flexible connectors and vibration dampers
- Engine and transmission mounting isolators
- High-speed train bogie suspension components
- Heavy-duty vehicle auxiliary system isolation
5.5 Process & Chemical Industry
- Heat exchanger and reactor vessel support systems
- High-purity chemical processing piping (316L grade)
- Pharmaceutical clean-room equipment isolation
- Food and beverage processing sanitary piping
5.6 Civil Engineering & Infrastructure
- Seismic isolation systems for bridges and buildings
- Railway track vibration dampening
- Large-diameter water supply and