Stainless Steel Coil Tube – Vertical Bright Annealing (BA) Furnace Process
Wenzhou Jixing Metal Materials Co., Ltd presents a premium-grade stainless steel coil tube (Coil Tube / 盘管) manufactured through an advanced Vertical Bright Annealing (BA) Furnace process. This technology represents the pinnacle of surface quality and metallurgical uniformity in stainless steel tubing, making it the preferred parent material for high-end Electropolishing (EP) tubes and mirror-finish tubes. The vertical configuration eliminates roller contact, ensuring a flawless surface finish with superior dimensional consistency.
Product Overview
The Vertical Bright Annealing (BA) furnace process is a specialized heat treatment technique applied to stainless steel coil tubing after cold drawing or cold rolling. Unlike conventional horizontal BA furnaces that utilize roller conveyor systems, the vertical BA furnace employs a gravity-driven suspension mechanism where the coil tube hangs vertically within the annealing chamber. This eliminates all mechanical contact between the workpiece and the furnace components, resulting in:
- Zero roller marks – No mechanical impression or indentation on the tube surface
- Gravity-uniform stress distribution – Even thermal and mechanical relaxation throughout the entire coil length
- Superior surface quality – Mirror-ready finish achievable without additional mechanical polishing
- Consistent metallurgical properties – Uniform grain structure and mechanical properties along the full coil
This process is exclusively reserved for applications demanding the highest surface integrity, including pharmaceutical-grade tubing, food processing equipment, optical components, and semiconductor manufacturing lines.
Material & Properties
Available Grades
| Grade | UNS Designation | Equivalent Standard | Primary Application |
|---|---|---|---|
| 304 / 304L | S30400 / S30403 | ASTM A213 / EN 10216-5 | General industrial, food & pharmaceutical |
| 316 / 316L | S31600 / S31603 | ASTM A269 / EN 10217-7 | Chemical processing, marine, high-corrosion |
| 321 | S32100 | ASTM A269 / EN 10216-5 | High-temperature applications |
| 904L | S90411 | ASTM B619 / EN 10217-7 | Extreme corrosion environments |
| 316Ti | S31635 | ASTM A269 / EN 10216-5 | Welded assemblies, high-temperature service |
Mechanical Properties (Post-Annealing, Grade 304/316L)
| Property | Specification | Test Method |
|---|---|---|
| Tensile Strength (Rm) | ≥ 520 MPa (75.4 ksi) | ASTM E8 / E8M |
| Yield Strength (Rp0.2) | ≥ 205 MPa (29.7 ksi) | ASTM E8 / E8M |
| Elongation (A50) | ≥ 40% | ASTM E8 / E8M |
| Hardness (HV) | ≤ 200 HV | ISO 6507 |
| Grain Size | ≥ ASTM No. 5 | ASTM E112 |
Surface Quality Specifications
| Parameter | Vertical BA Specification | Conventional Horizontal BA |
|---|---|---|
| Surface Roughness (Ra) | ≤ 0.4 μm (outer surface) | 0.6 – 1.0 μm |
| Surface Roughness (Ra) | ≤ 0.5 μm (inner surface) | 0.8 – 1.2 μm | Roller Mark | Absent (None) | Present (Typical) |
| Color Uniformity | Excellent – Single Hue | Good – Minor Variation |
| Reflectivity (Mirror Potential) | ≥ 95% achievable post-EP | 85 – 90% achievable post-EP |
Specifications
Dimensional Parameters
| Parameter | Range | Tolerance Class |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 168.3 mm (1/4" – 6") | ASTM A269 / EN 10217-7 |
| Wall Thickness | 0.5 mm – 6.35 mm (0.020" – 1/4") | ±0.10 mm or ±5% of nominal |
| Coil Length | Up to 3,000 m (per coil) | Continuous production |
| Coil Inner Diameter | 300 mm / 500 mm / 600 mm | Standard packaging |
| Roundness | ≤ 1% of OD | ISO 1130 |
| Straightness (per 1 m) | ≤ 1.0 mm | ASTM A269 |
Surface Finish Options
| Finish Designation | Description | Typical Ra (μm) | Application |
|---|---|---|---|
| BA (Bright Annealed) | Standard vertical BA finish | 0.4 – 0.6 | General high-quality applications |
| EP (Electropolished) | Post-BA electropolishing | 0.1 – 0.25 | Pharmaceutical, biotech, semiconductor |
| Mirror Polish | Mechanical + chemical mirror finish | ≤ 0.05 | Optical, decorative, instrumentation |
Manufacturing Process
Process Flow
- Coil Slitting & Cold Drawing: Raw stainless steel strip is slit to width and cold-drawn into tube form using precision PLC-controlled drawing dies, achieving tight dimensional tolerances.
- Coil Winding: The drawn coil tube is wound onto a precision-mandrel coil former with controlled tension to prevent deformation and maintain dimensional integrity.
- Vertical Bright Annealing: The coil is suspended vertically in a high-purity protective atmosphere furnace (typically N₂ + H₂ or dissociated ammonia NH₃) and heated to 1,050 – 1,150°C depending on grade. The vertical orientation ensures gravity-driven uniform heat distribution and eliminates all roller contact.
- Controlled Cooling: The coil is cooled under continued protective atmosphere to prevent oxidation and scale formation, maintaining the bright, clean surface.
- Surface Inspection: 100% visual inspection and automated surface scanning to verify absence of roller marks, scratches, or discoloration.
- Packaging: Coils are wrapped in protective film, placed in wooden or steel crates with desiccant for corrosion prevention during storage and transit.
Vertical BA Furnace – Technical Advantages
| Parameter | Vertical BA Furnace | Horizontal Roller BA Furnace |
|---|---|---|
| Workpiece Support | Gravity suspension (no contact) | Roller conveyor (mechanical contact) |
| Roller Mark Risk | Zero | Inherent |
| Temperature Uniformity | ±5°C (axial symmetry) | ±10 – 15°C |
| Protective Atmosphere Purity | O₂ + H₂O ≤ 10 ppm | O₂ + H₂O ≤ 20 – 50 ppm |
| Throughput | High (continuous batch) | Medium |
| Product Surface Quality | Premium (Mirror-ready) | Standard |
Key Process Parameters
- Annealing Temperature: 1,050°C – 1,150°C (1,922°F – 2,092°F)
- Heating Rate: 150°C/h (controlled to prevent thermal stress)
- Soak Time: 30 – 60 minutes (grade-dependent)
- Cooling Rate: 100°C/h under protective atmosphere
- Protective Gas: Dissociated Ammonia (NH₃ → N₂ + H₂) or N₂/H₂ mixture
- Dew Point: ≤ –60°C (dual dew point control)
- Oxygen & Water Content: ≤ 10 ppm combined
Applications
Target Industries
- Pharmaceutical & Biotechnology: Parent material for EP tubes used in CIP/SIP systems, bioreactors, and sterile transfer lines (FDA 21 CFR compliant)
- Semiconductor Manufacturing: Ultra-clean process tubing for chemical delivery systems (Class 1 cleanroom compatible)
- Food & Beverage Processing: Hygienic piping for dairy, brewery, and food-grade fluid transfer (EHEDG/3-A compliant)
- Optical & Instrumentation: Mirror-polished tubing for laser systems, spectrometers, and precision optical housings
- Medical Devices: Tubing for implant manufacturing, surgical instruments, and diagnostic equipment
- Chemical Processing: High-purity chemical transfer tubing requiring corrosion resistance and clean surfaces
- Aerospace: Precision tubing for fuel systems, hydraulic lines, and structural applications
Unique Selling Points
"Gravity-Driven Perfection" – The vertical BA furnace represents the gold standard in stainless steel coil tube surface quality. By eliminating all mechanical contact during annealing, we deliver a product with zero roller marks, superior reflectivity, and metallurgical uniformity that no conventional process can match.
- No Roller Marks: The vertical suspension eliminates the most common surface defect in conventionally processed BA tubing
- Mirror-Ready Surface: Achieves EP and mirror polish results with minimal post-processing, reducing downstream costs by 20–35%
- Metallurgical Uniformity: Gravity-driven heat flow ensures consistent grain structure and mechanical properties along the entire coil length
- End-to-End Traceability: Each coil is traceable from raw material mill certificate through final inspection
- Custom Configuration: Flexible in grade, dimension, length, and surface finish to meet specific project requirements
Quality Certifications & Standards Compliance
Applicable Standards
| Standard | Scope | Relevance |
|---|---|---|
| ASTM A269 | Stainless Steel Tube (seamless & welded) | Dimensional & mechanical specifications |
| ASTM A213 | Stainless Steel Tubing for Boilers | Material grade compliance |
| EN 10216-5 | Non-ferrous metal tubes – Technical delivery conditions | European dimensional standards |
| EN 10217-7 | Non-ferrous metal tubes – Heat exchangers | Heat transfer applications |
| ISO 1130 | Tubes – Roundness measurement | Geometric quality verification |
| ASTM E112 | Grain size determination | Microstructural verification |
| ASME BPE | Bioprocessing Equipment | Pharmaceutical-grade surface & cleanliness |
Quality Assurance Program
- Raw Material Traceability: 100% mill certificate verification for all incoming stainless steel coil
- In-Process Inspection: Automated surface scanning, dimensional gauging, and hardness testing at defined intervals
- Final Product Testing: Hydrostatic pressure testing (1.5× working pressure), dimensional verification, surface roughness measurement
- Cleanliness Verification: Particle count analysis and total organic carbon (TOC) testing for pharmaceutical-grade products
- Third-Party Certification: Available upon request (SGS, BV, TUV)
- Batch Traceability: Heat number, coil number, and process parameters recorded for every production batch
Available Certifications
- ISO 9001:2015 – Quality Management System
- ISO 1