Stainless Steel Coil Tube (Coiltube) – Internal Coil Tube Connection Assembly
Product Code: 919 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd (温州吉兴金属材料有限公司) | Category: Technical Literature & Engineering Reference
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular product designed for applications requiring flexible routing, heat exchange, fluid transport, and structural integration within confined spaces. Unlike straight seamless or welded pipes, coil tubes are formed into continuous helical or spiral configurations, enabling installation in environments where space constraints demand compact, bendable geometries. This product is specifically engineered to address the critical challenge of internal coil tube connection leakage — a well-documented failure mode in industrial piping systems involving helical coil assemblies.
Wenzhou Jixing Metal Materials Co., Ltd specializes in the production of high-purity stainless steel coil tubes that combine superior mechanical integrity, corrosion resistance, and dimensional accuracy. The company's coil tube products are manufactured to meet stringent international standards and are widely deployed across petrochemical, pharmaceutical, food processing, energy, and HVAC (Heating, Ventilation, and Air Conditioning) industries.
2. Material & Properties
2.1 Base Materials
- Austenitic Stainless Steel Grades: AISI 304 (UNS S30400), AISI 304L (UNS S30403), AISI 316 (UNS S31600), AISI 316L (UNS S31603), AISI 321 (UNS S32100), AISI 347 (UNS S34700)
- Duplex Stainless Steel Grades: UNS S31803 (2205), UNS S32750 (2507 Super Duplex)
- Custom Alloy Compositions: Available upon request for specialized service environments
2.2 Key Mechanical Properties (Typical — Grade 304/304L)
- Tensile Strength (UTS): ≥ 515 MPa (74,700 psi)
- Yield Strength (0.2% Offset): ≥ 205 MPa (29,700 psi)
- Elongation (at Break): ≥ 40%
- Hardness (HB): ≤ 201
- Modulus of Elasticity: 193 GPa (28,000,000 psi)
- Thermal Conductivity (at 100°C): 16.3 W/(m·K)
- Thermal Expansion Coefficient (20–100°C): 17.3 × 10⁻⁶ /°C
2.3 Corrosion Resistance
The austenitic stainless steel matrix provides excellent resistance to general atmospheric corrosion, organic acids, dilute inorganic acids, and chlorinated environments (particularly in 316/316L grades containing molybdenum). The internal coil tube connection design incorporates precision-welded joints and sealed interfaces to prevent leakage pathways that commonly arise from thermal cycling, vibration fatigue, and galvanic corrosion at dissimilar metal interfaces.
3. Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | Φ3.0 mm – Φ114.3 mm (1/8" – 4") | ASTM A213 / ASTM A269 |
| Wall Thickness | 0.3 mm – 6.0 mm (0.012" – 0.236") | ASTM A269 |
| Coil Diameter (Mean) | 50 mm – 500 mm (2" – 20") | Customer Specification |
| Coil Pitch / Spacing | 2 mm – 50 mm (adjustable) | Engineering Drawing |
| Length per Coil | 5 m – 50 m (16 ft – 164 ft) | ASTM A213 |
| Surface Finish | Mill Finish / 2B / No.4 Brushed / Electropolished (Ra ≤ 0.4 μm) | ASTM A478 |
| End Condition | Plain / Beveled / Threaded (BSPP, NPT) / Flanged | ASME B1.20.1 |
| Pressure Rating | Up to 16 MPa (PN16) at 20°C | ASME B31.3 / EN 13480 |
| Operating Temperature Range | −196°C to +800°C (−321°F to +1,472°F) | ASME VIII Div.1 |
| Welding Method | TIG (GTAW) / Orbital / Laser Butt Weld | ASME IX / ISO 3834 |
| Coating / Passivation | Citric Acid Passivation / Pickling / PTFE Internal Coating (optional) | ASTM A967 |
| Acceptance Criteria | 100% Visual Inspection + 100% Pressure Test + 10% PMI Verification | EN 10204 Type 3.1 |
4. Manufacturing Process
4.1 Process Flow
- Material Selection & Incoming Inspection: Raw stainless steel strip or seamless tube stock is procured from certified mills. Each batch undergoes spectroscopic analysis (PMI — Positive Material Identification) and mechanical property verification prior to processing.
- Slitting & Annealing: For coil-formed products, strip material is slit to precise width and undergoes solution annealing at 1050–1100°C in a protective atmosphere (argon or dew point-controlled dry hydrogen) to achieve full austenitic recrystallization and optimal corrosion resistance.
- Coil Forming (Cold Bending): The tube is cold-formed into helical coil geometry using precision CNC-controlled bending machinery. Forming parameters (bend radius, angular velocity, springback compensation) are calibrated to prevent wall thinning, ovality distortion, and residual stress accumulation. Post-forming dimensional inspection ensures conformity to ±0.5 mm tolerance on coil diameter.
- Connection Joint Fabrication: Internal coil tube connections are manufactured using orbital TIG (Tungsten Inert Gas) welding or laser butt welding. The welding process employs controlled heat input, shielding gas flow (argon at 10–15 L/min), and precise root gap management (0.1–0.5 mm) to produce full-penetration, leak-tight joints.
- Post-Weld Heat Treatment (PWHT): Where applicable, welded assemblies undergo solution annealing (1050°C ± 25°C, 30 min soak, water quench) to relieve welding residual stresses and restore full corrosion resistance in the Heat-Affected Zone (HAZ).
- Surface Treatment & Passivation: Finished coils undergo acid pickling (HNO₃/HF blend) and citric acid passivation per ASTM A967 to remove surface contaminants and establish a protective chromium oxide layer (Cr₂O₃).
- Non-Destructive Testing (NDT): All products undergo 100% pneumatic/hydrostatic pressure testing at 1.5× working pressure. Welded joints receive 100% visual inspection (VT) per ISO 17637. Random samples undergo 100% radiographic testing (RT) or ultrasonic testing (UT) per ASME V.
4.2 Leakage Prevention Design Features
The internal coil tube connection assembly incorporates several engineering improvements to address the root causes of leakage identified in field service:
- Stress-Relieved Coil Geometry: Residual stresses from cold forming are eliminated through controlled annealing, preventing stress-corrosion cracking (SCC) at connection interfaces.
- Full-Penetration Weld Integrity: Orbital welding with back-purging ensures no internal oxide inclusions or incomplete fusion at the root of welds.
- Thermal Expansion Accommodation: Coil pitch and support bracket design allow ±1.5% axial expansion without inducing joint shear stresses.
- Corrosion-Resistant Seal Materials: Gasket and seal components are matched to the base alloy grade to eliminate galvanic coupling and differential corrosion.
- Vibration Damping Supports: Anti-vibration mounting hardware is integrated at coil endpoints to mitigate fatigue cracking from process-induced oscillations.
5. Applications
5.1 Primary Application Domains
| Industry | Application | Key Requirement |
|---|---|---|
| Petrochemical & Oil/Gas | Reactor coil tubes, heat exchanger internals, separator internals | High-temperature resistance, H₂S corrosion resistance, pressure containment |
| Pharmaceutical & Biotech | Sterilization-in-place (SIP) coil assemblies, bioreactor heat transfer coils | Electropolished finish (Ra ≤ 0.4 μm), FDA/USP compliance, CIP compatibility |
| Food & Beverage Processing | Milk pasteurization coils, beer fermentation heat transfer, juice processing | 3-A Sanitary standards, non-toxic, easy-to-clean surfaces |
| HVAC & Refrigeration | Air-cooled heat exchangers, evaporator coils, condenser tubes | High thermal conductivity, frost resistance, low-pressure drop |
| Power Generation | Boiler economizer coils, superheater tubes, nuclear-grade feedwater heaters | Creep resistance, irradiation stability, ASME/NRC compliance |
| Automotive | Exhaust system heat exchangers, fuel cell cooling coils, turbocharger manifolds | Vibration resistance, thermal cycling durability, lightweight |
| Marine & Offshore | Seawater cooling coils, ballast water systems, subsea fluid transport | Chloride pitting resistance, biofouling resistance, high-cycle fatigue |
6. Quality Certifications & Compliance
6.1 International Certifications
- ISO 9001:2015 — Quality Management System
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health & Safety Management
- EN 10204 Type 3.1 — Inspection Certificates (Mill Test Reports with NDT data)
- ASME "S" Stamp — Sectional Heating Boiler & Boiler Code (where applicable)
- NACE MR0175 / ISO 15156 — Materials for Use in H₂S-Containing Environments in Oil and Gas Production
- NSF/ANSI 61 — Drinking Water System Components (for potable water applications)
- 3-A Sanitary Standards — Food Industry Equipment (for dairy, beverage, pharmaceutical)
- CE Marking — Conformity with EU Pressure Equipment Directive (PED 2014/68/EU)
- TÜV / Lloyd's Register / DNV — Third-party inspection and certification available
6.2 Testing & Verification Protocols
- Chemical Composition Analysis: Spectrographic verification per ASTM E415 / ASTM E135
- Mechanical Testing: Tensile, hardness, and impact testing per ASTM A370
- Corrosion Testing: Pitting resistance (PREN ≥ 19 for 316L), intergranular corrosion (ASTM A240), stress-corrosion cracking (ASTM G48)
- Pressure Testing: 100% hydrostatic test at 1.5× design pressure for 30 minutes hold
- Leak Testing: Helium mass spectrometer leak detection (detection limit: 1 × 10⁻⁹ Pa·m³/s) for critical applications
- Dimensional Inspection: CNC coordinate measuring machine (CMM) verification of coil geometry, OD, wall thickness, and pitch uniformity
7. Unique Selling Points
- Engineered Leakage Prevention: Proprietary connection design addressing root causes of coil tube joint failure through stress-relieved geometry, full-penetration weld integrity, and thermal expansion accommodation.
- Full Traceability: Every coil tube is traceable from raw material mill certificate through all manufacturing stages to final NDT documentation, ensuring complete supply chain transparency.
- Custom Engineering Capability: In-house CAD/CAM design support for non-standard coil geometries, custom pitch configurations, and application-specific connection interfaces.
- Multi-Grade Availability: Complete range from standard austenitic grades (304/316) to advanced duplex and super-austenitic alloys for extreme service conditions.
- Global Compliance: Products certified to meet ASME, EN, JIS, GB, and industry-specific standards, enabling seamless integration into international projects.