Stainless Steel Coil Tube — Solid Solution Treated (Item No. 933)
Product Overview
The Stainless Steel Coil Tube (盘管 / Coil Tube), designated as Item No. 933 by Wenzhou Jixing Metal Materials Co., Ltd., is a precision cold-worked tubular product delivered in coiled form to facilitate downstream processing, bending, and forming operations. This product is manufactured from austenitic stainless steel grades and undergoes a rigorous solid solution heat treatment (Solution Annealing) process to achieve optimal microstructural homogeneity, maximum corrosion resistance, and uniform mechanical properties throughout the tube wall.
Coil tubes are distinguished from cut-length (straight) tubes by their continuous helical delivery format, which eliminates butt welds, reduces material waste, and enables automated downstream forming. This product represents a critical intermediate material in the supply chain for heat exchangers, chemical processing equipment, pharmaceutical systems, and food-grade piping networks.
Material & Properties
The primary material grades employed for this coil tube product are austenitic stainless steels conforming to international standards including ASTM, EN, and GB specifications. The following material grades are typically available:
- ASTM A213 / EN 10216-5 / GB 13296 — Seamless stainless steel tubes for heat exchangers and general engineering
- ASTM A511 / EN 10217-7 — Welded stainless steel tubes for general engineering purposes
- ASTM A269 / EN 10217-7 — Austenitic stainless steel tubes for general service
Typical Chemical Composition (AISI 304 / 316L)
| Element | 304 (ASTM) | 316L (ASTM) |
|---|---|---|
| C (Carbon) | ≤ 0.08% | ≤ 0.030% |
| Mn (Manganese) | ≤ 2.0% | ≤ 2.0% |
| P (Phosphorus) | ≤ 0.045% | ≤ 0.045% |
| S (Sulfur) | ≤ 0.030% | ≤ 0.030% |
| Si (Silicon) | ≤ 1.0% | ≤ 1.0% |
| Cr (Chromium) | 18.0 – 20.0% | 16.5 – 18.5% |
| Ni (Nickel) | 8.0 – 10.5% | 10.0 – 14.0% |
| Mo (Molybdenum) | — | 2.0 – 3.0% |
| N (Nitrogen) | — | ≤ 0.10% |
| Fe (Iron) | Balance | Balance |
Mechanical Properties (Post Solid Solution Treatment)
| Property | Specification |
|---|---|
| Tensile Strength (σb) | ≥ 515 MPa (75 ksi) for 304; ≥ 485 MPa (70 ksi) for 316L |
| Yield Strength (σ0.2) | ≥ 205 MPa (30 ksi) |
| Elongation (A50mm) | ≥ 40% |
| Hardness (HB) | ≤ 217 HB (annealed condition) |
| Impact Energy (Charpy V-Notch, −40°C) | ≥ 47 J |
Specifications
| Parameter | Specification / Range |
|---|---|
| Product Form | Coil Tube (盘管 / Continuous Helical Coil) |
| Item No. | 933 |
| Outer Diameter (OD) | 6.0 mm – 108.0 mm (typical range) |
| Wall Thickness (WT) | 0.5 mm – 6.0 mm |
| OD Tolerance | ± 0.10 mm (± 0.10%) |
| Wall Thickness Tolerance | ± 10% (minimum ± 0.05 mm) |
| Coil Diameter (Core OD) | 150 mm / 200 mm / 250 mm / 300 mm (customizable) |
| Coil Length | Custom; typically 500 m – 5000 m per coil |
| Surface Finish | Pickled & Passivated (2B finish); optional electropolished or brushed |
| Heat Treatment Condition | Solution Annealed (Solid Solution Treated) |
| Solution Treatment Temperature | 1050°C – 1150°C (1922°F – 2092°F) |
| Cooling Method | Forced air quench / Water quench (rapid cooling) |
| Manufacturing Standard | ASTM A213 / A269 / A511; EN 10216-5 / 10217-7; GB 13296 |
| End Condition | Plain cut; optional beveled, threaded, or socket-welded ends |
| Protection | Plastic cap end protection; moisture-proof packaging |
Manufacturing Process
3.1 Raw Material Selection and Inspection
The manufacturing process begins with the procurement of certified stainless steel hot-rolled coils (HRC) or seamless tube blanks from approved mills. Incoming material undergoes rigorous inspection including:
- Chemical composition verification via Optical Emission Spectroscopy (OES)
- Mechanical property testing on sample coupons
- Visual surface inspection and dimensional verification
- Certification traceability (Mill Test Report / Certificate of Analysis)
3.2 Cold Drawing / Cold Rolling
The hot-rolled or annealed coil tube blanks are subjected to cold working (cold drawing or cold rolling) through precision dies or rolling mills to achieve the target outer diameter and wall thickness. This process induces work hardening, improves dimensional accuracy, and enhances surface finish quality. The reduction ratio is carefully controlled to maintain ductility while achieving desired mechanical strength.
3.3 Intermediate Annealing (if applicable)
For multi-pass cold working operations, intermediate annealing cycles may be required to relieve accumulated residual stresses and restore ductility. These intermediate anneals are conducted at 1050°C – 1100°C with controlled cooling rates to prevent chromium carbide precipitation (sensitization).
3.4 Solid Solution Heat Treatment (Solution Annealing)
The solid solution treatment is the critical metallurgical process that defines the final properties of this coil tube product. The process involves:
- Heating Phase: The coil tube is heated uniformly to 1050°C – 1150°C (1922°F – 2092°F) in a controlled atmosphere furnace (neutral or slightly reducing atmosphere) to dissolve all carbides, intermetallic phases, and precipitates into the austenitic matrix. The temperature is maintained (soaked) for a sufficient time to ensure complete homogenization, typically calculated as 15 minutes per 25 mm of wall thickness (minimum 1 hour).
- Quenching Phase: The tube is rapidly cooled (quenched) by forced air, water, or gas quenching to arrest the dissolution state and prevent precipitation of chromium carbides (Cr23C6) at grain boundaries. This rapid cooling preserves the single-phase austenitic microstructure.
- Stress Relief: A low-temperature stress relief cycle (≤ 600°C) may follow if required, though in the solution-annealed condition, residual stresses are typically minimal.
Metallurgical Significance: The solid solution treatment ensures that carbon, nitrogen, and other interstitial elements remain in solid solution within the face-centered cubic (FCC) austenite lattice. This maximizes the passive film-forming capability of chromium and molybdenum, thereby providing superior resistance to general corrosion, pitting corrosion, and intergranular corrosion (IGC). Failure to properly execute this process can result in sensitization — the precipitation of Cr23C6 at grain boundaries — leading to chromium depletion in adjacent regions and catastrophic loss of corrosion resistance.
3.5 Pickling and Passivation
Following the solution treatment, the coil tube surface undergoes pickling (removal of oxide scale using a mixture of nitric acid and hydrofluoric acid or citric acid) and passivation (chemical enrichment of the surface chromium content to promote spontaneous formation of the protective Cr2O3 passive film). This step is essential for achieving the required surface cleanliness and long-term corrosion performance.
3.6 Dimensional Verification and Quality Control
Post-treatment dimensional inspection includes:
- Outer diameter measurement (micrometer / laser gauge)
- Wall thickness verification (ultrasonic thickness gauge)
- Roundness and straightness assessment
- Coil flatness and edge condition inspection
3.7 Final Testing and Certification
- Tensile testing (ASTM E8)
- Hardness testing (ASTM E92 — Rockwell/Brinell)
- Corrosion testing (ASTM A923 — intergranular corrosion; ASTM G48 — pitting resistance)
- Hydrostatic or pneumatic pressure testing (where applicable)
- Non-destructive testing: Eddy current (ECT) for surface and near-surface defect detection
3.8 Packaging and Delivery
The finished coil tubes are wound onto appropriate cores, wrapped with moisture-proof protective film, and secured with steel strapping. End caps are installed to prevent contamination. Each coil is labeled with product identification, heat number, grade, dimensions, and traceability codes.
Applications
The solid solution treated stainless steel coil tube (Item No. 933) finds extensive application across multiple high-performance industries:
- Heat Exchangers and Condensers: Shell-and-tube heat exchangers, air-cooled condensers, evaporators, and refrigeration coils where high thermal efficiency and corrosion resistance are paramount.
- Chemical Processing: Piping systems for aggressive chemical environments including sulfuric acid, phosphoric acid, and halide-containing solutions (particularly with 316L grade).
- Pharmaceutical and Bioprocessing: GMP-compliant piping for pharmaceutical manufacturing, sterile fluid transfer, and bioreactor connections requiring electropolished or sanitary-grade surfaces.
- Food and Beverage Processing: Hygienic piping systems for dairy, brewing, and food-grade applications requiring high surface finish and resistance to organic acid corrosion.
- Petrochemical and Oil & Gas: Downstream processing equipment, refinery piping, and offshore platforms where chloride-induced stress corrosion cracking (SCC) resistance is critical.
- Automotive and Aerospace: Exhaust systems, fuel lines, and structural components requiring high-temperature oxidation resistance and fatigue performance.
- Architectural and Decorative: Handrails, escalator components, and structural elements in coastal or high-moisture environments.
- Medical Devices: Endoscopes, surgical instrument tubing, and implant-grade applications (where specified grades meet ISO 13485 requirements).
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system ensuring product conformity to international standards:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System — ensures consistent product quality and continuous improvement |
| ISO 14001:2015 | Environmental Management System — sustainable manufacturing practices |
| ISO 45001:2018 | Occupational Health and Safety Management System |
| EN 10204 3.1 | Inspection Certificate — independent third-party inspection of material properties |
| EN 10 |