Stainless Steel Coil Tube — Offline Bulk Solution Annealed
Product Overview
Wenzhou Jixing Metal Materials Co., Ltd. offers premium-grade stainless steel coil tubes processed through an offline bulk solution annealing treatment. Unlike conventional inline or sectional heat treatment methods, this product undergoes a complete furnace-based solution annealing process where the entire coil tube is loaded into the furnace as a single unit. This ensures that every segment of the coil tube receives uniform thermal exposure, resulting in the most homogeneous microstructure and mechanical property distribution achievable in coil tube manufacturing.
This approach is the industry's gold standard for applications demanding consistent performance along the entire tube length, eliminating the property gradients and stress concentrations that can arise from segmented or partial heat treatment methods.
Material & Properties
These coil tubes are manufactured from austenitic and austenitic-ferritic stainless steel grades, including but not limited to:
- 304 / 304L — Excellent corrosion resistance and formability
- 316 / 316L — Superior resistance to pitting and crevice corrosion
- 321 — Stabilized against intergranular corrosion at elevated temperatures
- 316L NACE — Enhanced resistance for oil and gas environments
The offline bulk solution annealing process guarantees the following material advantages:
- Complete dissolution of carbides and intermetallic phases into the austenitic matrix
- Total elimination of cold-work residual stresses throughout the entire tube length
- Maximum uniformity of mechanical properties (tensile strength, yield strength, elongation)
- Optimized grain structure free of directional anisotropy
- Full restoration of corrosion resistance to the parent alloy's design potential
Specifications
| Parameter | Specification |
|---|---|
| Product Form | Coil Tube (Continuous Coil Winding) |
| Manufacturing Process | Offline Bulk Solution Annealing (Entire Tube Furnace Treatment) |
| Standard Grades | 304, 304L, 316, 316L, 321, 316L NACE, Custom Grades |
| Outer Diameter (OD) | 3.0 mm – 168.3 mm (custom sizes available) |
| Wall Thickness | 0.3 mm – 6.35 mm (tolerance ±0.1 mm or as specified) |
| Coil Length | Up to 1,000 m per coil (continuous) |
| Surface Finish | 2B, BA, No.4, No.8, Mirror, Pickled & Passivated |
| Heat Treatment | 1050°C – 1150°C Solution Anneal with Rapid Quench |
| Residual Stress | Effectively Eliminated (Full Relief) |
| Property Uniformity | Maximum — No Longitudinal or Transverse Variation |
| Applicable Standards | ASTM A213/A269, ASME SA-213/SA-269, EN 10216-5, GB/T 12771 |
| End Condition | Plain End, Beveled End, or as Specified |
Manufacturing Process
1. Raw Material Selection & Pipe Blank Preparation
High-purity stainless steel billets are sourced from certified mills and inspected for chemical composition and inclusion content. Pipe blanks are drawn and formed to the required OD and wall thickness specifications.
2. Coil Winding
The formed tube is wound onto a coil former to produce the continuous coil tube configuration, ready for downstream processing and heat treatment.
3. Offline Bulk Solution Annealing — Core Differentiator
This is the defining process step that sets this product apart from standard coil tube offerings:
- Full-Load Furnace Charging: The entire coil tube is loaded into a dedicated batch-type annealing furnace as a single continuous unit. No cutting, segmentation, or partial loading occurs.
- Controlled Heating Cycle: The furnace is ramped at a precisely controlled rate (typically 2–5°C/min) to the target solution annealing temperature of 1050°C–1150°C, ensuring even thermal penetration throughout the coil mass.
- Hold Time: The entire coil is held at peak temperature for the required duration to fully dissolve carbides, precipitates, and segregation phases into the solid solution.
- Rapid Quench: Upon completion of the hold period, the entire coil is rapidly cooled (air quench or forced convection) to suppress re-precipitation and lock in the homogeneous solution structure.
- Stress Relief Verification: Post-anneal inspection confirms complete residual stress elimination across the full coil length.
4. Pickling & Passivation
The annealed coil tube undergoes acid pickling to remove oxide scale, followed by passivation treatment to restore and enhance the protective chromium oxide surface film.
5. Final Inspection & Testing
Every coil lot undergoes comprehensive verification including:
- Hydrostatic pressure testing (100% of coils)
- Dimensional inspection (OD, wall thickness, roundness, straightness)
- Mechanical property testing at multiple points along the coil to verify uniformity
- Chemical analysis (spectrographic verification)
- Surface quality visual and automated inspection
- Corrosion resistance testing (as required by specification)
Unique Selling Points
- Industry-Leading Property Uniformity: The offline bulk solution annealing process ensures that every point along the coil tube — from the first meter to the last — exhibits identical mechanical and metallurgical properties. This is unachievable with sectional or inline heat treatment methods.
- Complete Residual Stress Elimination: By treating the entire tube as a single furnace charge, all cold-work stresses from forming, drawing, and coiling are fully relieved, preventing distortion during downstream welding, forming, or service.
- Superior Corrosion Resistance: Full solution annealing guarantees maximum chromium and nickel availability at grain boundaries, delivering optimal resistance to intergranular corrosion, pitting, and stress corrosion cracking.
- Reduced Variability Risk: Eliminates the property discontinuities and potential weak points that arise at heat-treatment joints in segmented processing.
- Consistent Weldability: Uniform microstructure throughout the coil ensures predictable and reliable welding performance at any point along the tube length.
Applications
Stainless steel coil tubes with offline bulk solution annealing are specified for the most demanding applications where property uniformity and complete stress relief are non-negotiable:
- Heat Exchanger Manufacturing: Coil tube for shell-and-tube heat exchangers, condensers, and evaporators requiring consistent thermal conductivity and corrosion resistance
- Food & Beverage Processing: Hygienic-grade tubing for CIP/SIP systems, pasteurization lines, and brewing equipment
- Pharmaceutical Equipment: GMP-compliant piping and heat exchange components requiring verified material homogeneity
- Chemical Processing: Reactor internals, distillation column components, and corrosive fluid handling systems
- Oil & Gas Industry: Downhole tubing, wellhead assemblies, and subsea production systems (316L NACE grades)
- Power Generation: Boiler feedwater systems, turbine condensers, and nuclear-grade heat transfer applications
- Automotive Industry: Exhaust system components, turbocharger manifolds, and fuel cell cooling loops
- Medical Devices: Surgical instrument tubing and implant-grade coil components
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains rigorous quality management systems to ensure every coil tube meets or exceeds international standards:
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001 — Environmental Management System Certification
- EN 10204 3.1 — Full Third-Party Inspection Certificates available
- NACE MR0175/ISO 15156 — Compliance for sour service applications
- CE / PED 2014/68/EU — Pressure Equipment Directive compliance
- ASME Stamp — Available for pressure vessel and piping components
- Mill Test Certificates (MTC) — Provided with every shipment, including heat treatment documentation
Each coil lot is accompanied by a comprehensive mill test report documenting chemical composition, mechanical properties, heat treatment parameters (furnace temperature profiles, hold times, cooling rates), dimensional measurements, and hydrostatic test results. Full traceability from raw material mill heat number through final product identification is maintained.
Note: The offline bulk solution annealing process represents the highest tier of heat treatment available for stainless steel coil tubes. It is recommended for any application where property consistency along the full tube length is critical to performance, safety, or regulatory compliance. For custom specifications or grade requirements, please contact Wenzhou Jixing Metal Materials Co., Ltd. for detailed technical consultation and quotation.