Stainless Steel Pressure-Bearing Coil Tube (Coil Tube) — Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (盘管, Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a specialized pressure-bearing tubular component engineered for demanding industrial and process engineering applications. Unlike conventional straight-length pipes, coil tubes are formed into continuous helical or spiral configurations, enabling high surface-area-to-volume ratios essential for heat exchange, pressure containment, and fluid distribution systems.
This product category encompasses cold-formed and hot-formed coil tubes designed in accordance with international standards governing pressure vessel and piping design. The design methodology for pressure-bearing coil tubes integrates considerations of hoop stress, bending stress, torsional loading, and thermal fatigue to ensure structural integrity under operational conditions. Wenzhou Jixing Metal Materials applies rigorous engineering analysis — including finite element method (FEM) simulation and analytical stress calculations — to optimize coil geometry, wall thickness, and material selection for specific service environments.
Key Design Principle: The design of pressure-bearing coil tubes requires special attention to the interaction between radial pressure loading and the geometric curvature of the coil. The combined stress state — comprising membrane stress, bending stress, and secondary stress — must be evaluated against allowable stress limits per applicable codes such as ASME BPV Section VIII and EN 13445.
2. Material & Properties
2.1 Material Grades
The coil tubes are fabricated from a range of austenitic and duplex stainless steel grades, selected based on corrosion resistance requirements, temperature exposure, and mechanical property demands:
- 304 / 304L (UNS S30400 / S30403): General-purpose austenitic stainless steel with excellent corrosion resistance in atmospheric and mildly corrosive environments.
- 316 / 316L (UNS S31600 / S31603): Molybdenum-enhanced austenitic grade offering superior resistance to pitting and crevice corrosion in chlorinated and acidic media.
- 321 / 321H (UNS S32100 / S32109): Titanium-stabilized grade suitable for high-temperature service up to 870°C, resistant to intergranular corrosion.
- 316L Duplex (UNS S31803 / S32205): Duplex austenite-ferrite microstructure providing elevated yield strength (≥450 MPa) and exceptional resistance to chloride stress corrosion cracking (Cl-SCC).
2.2 Mechanical Properties
| Property | 304L | 316L | 321H | 2205 Duplex |
|---|---|---|---|---|
| Tensile Strength (Rm) — Minimum | 485 MPa | 485 MPa | 515 MPa | 550 MPa |
| Yield Strength (Rp0.2) — Minimum | 170 MPa | 170 MPa | 205 MPa | 450 MPa |
| Elongation (A5) — Minimum | 40% | 40% | 40% | 25% |
| Impact Energy (V-Notch, −40°C) | ≥ 47 J | ≥ 47 J | ≥ 47 J | ≥ 70 J |
2.3 Chemical Composition (Typical, wt%)
| Element | 304L | 316L | 2205 Duplex |
|---|---|---|---|
| C | ≤ 0.030 | ≤ 0.030 | ≤ 0.030 |
| Cr | 18.0 – 20.0 | 16.0 – 18.0 | 22.0 – 23.0 |
| Ni | 8.0 – 12.0 | 10.0 – 14.0 | 4.5 – 6.5 |
| Mo | — | 2.0 – 3.0 | 3.0 – 3.5 |
| N | — | — | 0.14 – 0.20 |
| Fe | Balance | Balance | Balance |
3. Specifications
| Parameter | Specification |
|---|---|
| Product Name | Stainless Steel Coil Tube (Coiltube / 盘管) |
| Product Code | 1205 |
| Manufacturer | Wenzhou Jixing Metal Materials Co., Ltd. |
| Coil Outer Diameter (COD) | Φ100 mm – Φ6,000 mm (customizable) |
| Tube Outer Diameter (OD) | Φ6.0 mm – Φ108.0 mm |
| Wall Thickness | 0.5 mm – 8.0 mm |
| Tube Length per Coil | Up to 500 m (continuous) |
| Coil Pitch (P) | 15 mm – 200 mm (adjustable) |
| Number of Turns | 1 – 5,000 turns |
| Design Pressure Range | 0.1 MPa – 40.0 MPa |
| Design Temperature Range | −196°C to +650°C |
| Surface Finish | 2B, BA (Bright Annealed), No. 4 Brushed, Mirror (Ra ≤ 0.1 μm) |
| End Treatment | Plain end, Beveled, Threaded, Flanged, or Custom Fitting |
| Applicable Standards | ASTM A213, ASTM A269, ASME SA-213, EN 10216-5, GB/T 12770, GB/T 14976 |
| Packaging | Wooden crate, steel frame, or export-grade protective wrapping |
4. Manufacturing Process
4.1 Raw Material Selection and Inspection
Hot-rolled stainless steel strip or seamless tube stock is procured from certified mills with full traceability. Incoming material undergoes spectroscopic chemical analysis (OES), tensile testing, hardness testing, and grain boundary structure verification to confirm conformance with the specified grade.
4.2 Forming and Coiling
The coil tube formation process follows a multi-stage sequence:
- Preforming: The straight tube or strip is fed through a series of progressive roll-forming stations that gradually bend the material to the target coil radius while controlling springback compensation.
- Coiling: A precision coiling machine wraps the preformed tube into the specified helical geometry. The coil diameter, pitch, and turn count are controlled via CNC (Computer Numerical Control) systems to ensure dimensional accuracy within ±0.5% tolerance.
- Welding (if applicable): For welded coil tubes, longitudinal or spiral weld seams are produced via TIG (Tungsten Inert Gas) welding or orbital welding, followed by visual inspection (VT) and dye penetrant testing (PT).
4.3 Heat Treatment and Stress Relief
Following coiling, the tube assembly undergoes solution annealing (typically 1,050°C – 1,100°C for austenitic grades, followed by water quenching) to restore full solution-strengthened microstructure and relieve residual stresses introduced during cold forming. This step is critical for pressure-bearing applications to prevent delayed stress corrosion cracking and ensure uniform mechanical properties throughout the coil.
4.4 Surface Treatment and Finishing
Post-annealing pickling and passivation remove mill scale and surface contaminants, restoring the chromium oxide passive layer. Additional surface finishing — including electropolishing, mechanical polishing, or passivation — is performed per customer specification to achieve the required surface roughness and corrosion resistance.
4.5 Pressure Testing and Non-Destructive Testing (NDT)
Each coil tube lot undergoes comprehensive quality verification:
- Hydrostatic Pressure Test: Conducted at 1.5× the design pressure per ASTM A315 or ASME BPV Section VIII, with a minimum hold time of 60 seconds.
- Helium Leak Testing: For high-vacuum or nuclear-grade applications, helium mass spectrometer leak detection is performed at a sensitivity of ≤ 1×10⁻⁹ Pa·m³/s.
- Eddy Current Testing (ECT): Full-length automated ECT scanning detects wall thickness variations, surface defects, and subsurface discontinuities.
- Visual Inspection (VT): 100% visual examination of weld seams, coil geometry, and surface condition per ASME Section V, Article 1.
5. Applications
Stainless steel pressure-bearing coil tubes are deployed across a broad spectrum of industries where reliable containment of fluids under pressure, thermal cycling, or corrosive media is critical:
- Oil & Gas Industry: Subsea production risers, wellhead flow lines, gas lift coils, and heat tracing systems. Duplex 2205 coils are preferred for sour service (H2S-containing environments) per NACE MR0175/ISO 15156 compliance.
- Petrochemical and Refinery: Heat exchanger bundles, reboiler coil tubes, distillation column internals, and high-pressure transfer lines.
- Power Generation: Boiler economizer coils, superheater tubes, feedwater preheating coils, and nuclear reactor coolant loop components.
- Pharmaceutical and Bioprocessing: CIP (Clean-In-Place) systems, sterile fluid transfer coils, reactor jacket coils, and autoclave components requiring electropolished surfaces (Ra ≤ 0.4 μm).
- Food and Beverage Processing: Pasteurization heat exchangers, sanitary-grade transfer coils, and beverage carbonation systems.
- Chemical Processing: Aggressive chemical storage and transfer coils, acid-resistant heat exchangers, and corrosion-resistant pressure vessels.
- LNG (Liquefied Natural Gas) Systems: Cryogenic coil tubing for LNG storage and vaporization systems operating at temperatures as low as −196°C.
- Marine and Offshore: Ballast water treatment systems, desalination plant heat exchangers, and subsea manifold coil assemblies.
6. Quality Certifications and Compliance
6.1 Management System Certifications
- ISO 9001:2015 — Quality Management System (QMS) certification ensuring consistent product quality and process control.
- ISO 14001:2015 — Environmental Management System (EMS) certification for sustainable manufacturing practices.
- ISO 45001:2018 — Occupational Health and Safety Management System certification.
- ISO 3834-2 — Quality requirements for fusion welding of metallic materials (welded coil tube production).
6.2 Product and Material Certifications
- EN 10204 3.1 / 3.2 — Inspection certificates issued by authorized inspection bodies (e.g., TUV, Lloyd's Register, Bureau Veritas).
- ASME "S" Stamp / "U" Stamp — Authorization for fabrication of pressure-containing components per ASME Boiler and Pressure Vessel Code.
- API Monogram — American Petroleum Institute certification for oil and gas industry components (where applicable).
- NACE MR0175 / ISO 15156 — Compliance with materials requirements for sour service environments.
- PED (Pressure Equipment Directive) 2014/68/EU — Conformity assessment for pressure equipment marketed within the European Economic Area.
- CRN (Canadian Registration Number) — Authorization for pressure equipment in Canadian jurisdictions.
6.3 Traceability and Documentation
Each coil tube shipment is accompanied by a comprehensive documentation package including:
- Mill Test Certificate (MTC) with full chemical and mechanical property data
- Heat number traceability records from raw material to finished product
- Welding Procedure Specification (WPS) and Welding Procedure Qualification Record (WPQR) for welded assemblies
- Non-Destructive Examination (NDE) reports with acceptance criteria references
- Hydrostatic pressure test certificates with date, pressure, and hold time records
- Dimensional inspection reports with as-built geometry data
- Material traceability matrix linking coil tube heat numbers to upstream mill certifications
7. Unique Selling Points
- Engineering-Driven Design: Wenzhou Jixing Metal Materials applies rigorous pressure-bearing design methodologies — integrating analytical stress analysis, FEM simulation, and code compliance verification — to ensure coil tubes meet exacting performance requirements under complex loading conditions.
- Custom Geometric Flexibility: Full customization of coil diameter, pitch, turn count, and tube dimensions enables seamless integration into proprietary heat exchanger, reactor, and process equipment designs.
- Multi-Grade Material Expertise: Capability to supply austenitic, super-austenitic, and duplex stainless steel coil tubes covers the full spectrum of corrosion and mechanical performance requirements.
- Comprehensive Quality Assurance: End-to-end traceability, multi-modal NDT, and third-party inspection body certification ensure zero-defect delivery for critical safety applications.