Stainless Steel Coil Tube — Fully Soft Annealed Condition (Annealed/O)
Product Overview
The Stainless Steel Coil Tube in Fully Soft Annealed Condition (Designation: Annealed/O) is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product represents the ultimate in ductility and formability within the stainless steel coil tube family, achieved through a fully recrystallized microstructure obtained via controlled solution annealing. The "Fully Soft" designation indicates that the material has been subjected to a complete annealing cycle, resulting in maximum elongation, minimum hardness, and exceptional cold-workability — making it the preferred choice for applications requiring severe forming, deep drawing, bending, and expansion operations.
Coil tubes (盘管) are produced in continuous coil form, enabling high-efficiency downstream processing through automated forming lines. The fully soft annealed condition eliminates residual stresses from prior cold working, ensuring predictable material behavior during subsequent fabrication steps.
Material & Properties
The fully soft annealed coil tube is typically manufactured from austenitic stainless steel grades, most commonly 304 (UNS S30400) and 316 (UNS S31600), though other grades such as 321, 304L, 316L, and duplex alloys may be available upon request. The annealing treatment fully recrystallizes the austenitic microstructure, dissolving any cold-work-induced dislocation density and restoring maximum formability.
Key Mechanical Characteristics:
- Low Hardness: Vickers Hardness (HV) ≤ 180, indicating a fully recrystallized, stress-free microstructure with minimal dislocation density.
- High Elongation: Elongation at Break ≥ 40%, demonstrating exceptional ductility and the capacity to undergo significant plastic deformation without fracture.
- Superior Formability: The combination of low hardness and high elongation enables the tube to withstand complex forming operations including deep drawing, severe bending, and cold expansion.
- Excellent Bendability: Minimum bending radius of approximately 3 × Outer Diameter (OD), allowing tight-radius bends without cracking or wall thinning.
- High Expansion Capacity: Expansion rate ≥ 30%, permitting significant cold expansion of tube ends for seamless fittings, flanges, and end connections.
Specifications
| Parameter | Specification | Notes |
|---|---|---|
| Product Type | Stainless Steel Coil Tube (Coiltube) | Continuous coil form |
| Mechanical Condition | Annealed / Fully Soft (O) | Complete recrystallization |
| Vickers Hardness (HV) | ≤ 180 HV | Measured per ASTM E92 |
| Elongation at Break | ≥ 40% | Measured per ASTM E8 |
| Minimum Bending Radius | ≈ 3 × OD | Without cracking or wall failure |
| Cold Expansion Rate | ≥ 30% | End expansion / flaring capacity |
| Typical Grades | 304, 316, 304L, 316L, 321 | Custom grades available |
| Surface Finish | Pickled & Passivated (2B / BA) | Protective passive film |
| Coil Form | Continuous coil, center-supported | Custom coil weights available |
| Standards Compliance | ASTM A269 / A213 / EN 10216-5 | Grade-specific standards |
Manufacturing Process
The production of fully soft annealed stainless steel coil tubes follows a rigorous multi-stage process:
- Hot Rolling: Stainless steel billets are hot-rolled into seamless tubes or welded pipe blanks at elevated temperatures (typically 1100–1200°C) to achieve initial dimensional requirements.
- Cold Drawing / Cold Drawing & Sizing: The hot-rolled tube is cold-drawn through precision dies to achieve tight dimensional tolerances, superior surface finish, and enhanced mechanical properties. This introduces work hardening and residual stresses.
- Coiling: The cold-drawn tube is coiled into continuous lengths for efficient handling and downstream processing.
- Pickling & Passivation: The coil is subjected to chemical pickling (typically using a mix of hydrochloric and nitric acid) to remove surface scale and contaminants, followed by passivation to restore the protective chromium oxide layer.
- Solution Annealing (Key Step): The coiled tube is heated to the recrystallization temperature range (typically 1050–1150°C for austenitic grades) in a protective atmosphere (vacuum or inert gas) to fully dissolve cold-work-induced dislocations and restore the equilibrium austenitic microstructure. This is followed by rapid controlled cooling (quenching) to prevent grain growth.
- Final Inspection & Testing: Each coil undergoes mechanical testing (hardness, tensile, elongation), dimensional verification, and surface inspection to confirm compliance with the fully soft specification.
Applications
The fully soft annealed condition makes this coil tube uniquely suited for applications demanding maximum formability:
- Automotive Industry: Fuel cell systems, hydrogen piping, brake lines, and complex exhaust routing requiring tight bends and flared connections.
- Medical & Pharmaceutical Equipment: Sanitary tubing for deep-drawn fittings, valve bodies, and hygienic connections requiring autoclavable, crevice-free joints.
- Food Processing Equipment: Sanitary piping systems with expanded ends, flared fittings, and complex routing for CIP/SIP compatibility.
- Chemical Processing: Heat exchanger tubes requiring tube-end expansion into headers, and process piping with numerous bends and fittings.
- Ornamental & Architectural: Decorative railings, handrails, and structural elements requiring tight-radius bending and custom shaping.
- Hydraulic & Pneumatic Systems: High-pressure lines requiring formed fittings, swaged connections, and complex routing.
- Heat Exchangers & Boilers: Tubes requiring cold expansion into tube sheets and headers without cracking.
- Instrumentation & Process Piping: Precision tubing for analytical instruments, chromatography systems, and flow control assemblies.
Quality Certifications & Testing
Wenzhou Jixing Metal Materials Co., Ltd maintains rigorous quality assurance protocols for all coil tube products:
- ISO 9001:2015 — Quality Management System certification ensuring consistent production quality.
- ISO 14001 — Environmental Management System compliance for sustainable manufacturing.
- CE Marking — European conformity for pressure equipment and piping applications (PED 2014/68/EU).
- Mill Test Certificates (MTC / EN 10204 3.1) — Full traceability documentation for each production batch.
- Third-Party Inspection — Available upon request (SGS, BV, TUV, etc.).
Testing Methods Include:
- Hardness Testing per ASTM E92 (Vickers)
- Tensile Testing per ASTM E8 (yield strength, ultimate tensile strength, elongation)
- Hydrostatic Pressure Testing per ASTM A269
- Chemical Analysis per ASTM E415 (OES / Spark Spectrometry)
- Dimensional Inspection per ASTM A213 / A269 tolerances
- Surface Passivation Verification per ASTM A967
- Intergranular Corrosion Testing per ASTM A240 (where applicable)
Unique Selling Points
Exceptional Formability: The HV ≤ 180 and elongation ≥ 40% combination provides unmatched cold-workability among stainless steel coil tubes, enabling complex geometries that are impossible with cold-worked or partially annealed conditions.
Seamless Fitting Creation: The ≥ 30% cold expansion rate allows for the creation of leak-tight, mechanically strong end connections without welding, reducing porosity risk and improving pressure integrity.
Continuous Coil Efficiency: Delivered in coil form for maximum downstream processing efficiency, minimizing material waste through automated cutting, bending, and forming operations.
Full Recrystallization: Unlike partially annealed conditions, the fully soft state eliminates all residual stresses, ensuring predictable and repeatable forming behavior across the entire coil length.
Multi-Grade Availability: Available in a wide range of austenitic and specialty grades to meet diverse corrosion, temperature, and mechanical requirements across industries.