316L Austenitic Stainless Steel Coil Tube — Low-Carbon Molybdenum-Bearing Grade
1. Product Overview
The 316L Coil Tube is a premium-grade austenitic stainless steel coil tube manufactured by Wenzhou Jixing Metal Materials Co., Ltd. Designed within the austenitic-corrosion-resistant category, this product combines the benefits of a low-carbon (L) matrix with the addition of molybdenum (Mo), delivering exceptional resistance to both pitting corrosion and intergranular corrosion. The coil form factor enables efficient downstream processing, including cold drawing, cutting, forming, and welding, making it an ideal semi-finished product for high-purity piping systems.
As a coil tube, the product is supplied in a continuous coiled configuration, minimizing material waste and optimizing material utilization rates for mass-production environments. The 316L designation places it among the most widely specified grades in sanitary, pharmaceutical, and marine engineering sectors worldwide.
2. Material Composition & Metallurgical Properties
2.1 Chemical Composition (ASTM A270 / EN 10216-5)
| Element | Symbol | Specification (%) | Role in Alloy |
|---|---|---|---|
| Carbon (Maximum) | C | ≤ 0.030 | Ultra-low carbon minimizes chromium carbide precipitation, preventing sensitization and intergranular corrosion |
| Chromium | Cr | 16.0 – 18.0 | Forms passive oxide layer; primary driver of general and pitting corrosion resistance |
| Nickel | Ni | 10.0 – 14.0 | Stabilizes austenitic structure; enhances ductility and toughness at low temperatures |
| Molybdenum | Mo | 2.0 – 3.0 | Critical addition for chloride pitting and crevice corrosion resistance; improves resistance in reducing acid environments |
| Manganese | Mn | ≤ 2.0 | Auxiliary austenite stabilizer |
| Silicon | Si | ≤ 1.0 | Deoxidizer; improves high-temperature oxidation resistance |
| Phosphorus (Maximum) | P | ≤ 0.045 | Impurity; limited to maintain ductility and corrosion performance |
| Sulfur (Maximum) | S | ≤ 0.030 | Impurity; limited to prevent inclusion-related defects |
2.2 Physical Properties
- Density: 8.0 g/cm³
- Specific Heat Capacity: 0.5 kJ/(kg·K) at 20 °C
- Thermal Conductivity: 14.5 W/(m·K) at 300 K
- Modulus of Elasticity: 193 GPa
- Melting Range: 1375 – 1400 °C
- Maximum Service Temperature: 870 °C (oxidation); 425 °C (mechanical strength retention)
2.3 Mechanical Properties (Annealed Condition)
- Tensile Strength (Rm): ≥ 485 MPa (≥ 70 ksi)
- Yield Strength (Rp0.2): ≥ 170 MPa (≥ 25 ksi)
- Elongation (A50): ≥ 40 %
- Hardness: ≤ 217 HBW / ≤ 95 HRB
2.4 Corrosion Resistance Characteristics
- Pitting Resistance: PREN (Pitting Resistance Equivalent Number) of approximately 24–26, significantly exceeding 304/304L grades. The molybdenum addition provides superior performance in chloride-containing environments.
- Intergranular Corrosion Resistance: The ultra-low carbon content (≤ 0.03 % C) eliminates the risk of chromium carbide precipitation at grain boundaries during welding or heat exposure in the sensitization range (450–850 °C), ensuring excellent resistance to intergranular attack without the need for post-weld stabilization heat treatment.
- Crevice Corrosion Resistance: Enhanced by Mo content, suitable for tight-fitting joints and gasketed connections.
- Stress Corrosion Cracking (SCC): Low susceptibility in chloride environments at moderate temperatures compared to 304-series grades.
3. Technical Specifications
| Parameter | Specification | |
|---|---|---|
| Product Form | Coil Tube (Continuous Coiled Configuration) | |
| Material Grade | 316L (UNS S31603 / EN 1.4404 / GB 022Cr17Ni12Mo2) | |
| Applicable Standards | ASTM A270, ASTM A269, EN 10216-5, EN 10217-7, GB/T 12771, GB/T 13296 | |
| Outer Diameter Range | Φ 3 mm – Φ 219 mm (custom sizes available upon request) | |
| Wall Thickness Range | 0.3 mm – 12 mm | |
| Coil Inner Diameter | 300 mm / 500 mm / 600 mm (configurable) | |
| Coil Length (Cut-to-Length Available) | Continuous coil or straight lengths 3 m – 12 m | |
| Surface Finish | Pickled & Passivated (2B), Mill Finish, or Custom (BA — Bright Annealed, Electropolished, Brushed) | |
| Heat Treatment Condition | Solution Annealed (1050 – 1150 °C) followed by air or water quench | |
| Welding Suitability | Excellent — no preheating required; no post-weld heat treatment needed due to low carbon content | |
| Non-Magnetic | Yes (ferrite content ≤ 3 % by design; cold working may introduce slight magnetism) | |
| Packaging | Export-grade wooden crates, VCI paper wrapping, moisture-proof inner lining; seaworthy packaging available | |
4. Manufacturing Process
The production of 316L coil tube at Wenzhou Jixing Metal Materials Co., Ltd follows a rigorously controlled metallurgical and mechanical processing sequence:
- Raw Material Selection: Certified 316L stainless steel strip (cold-rolled coil) is sourced from approved mills with full mill test certificates (MTC) verifying chemical composition and mechanical properties. Incoming material undergoes spectrographic analysis and hardness verification.
- Coil Forming (Cold Roll Forming): The flat strip is fed through a series of progressive roll stations that gradually bend the material into the desired circular cross-section. Precision tooling ensures dimensional accuracy and uniform wall thickness throughout the coil length.
- Seam Welding (TIG / Laser): The formed tube is welded along the longitudinal seam using either Tungsten Inert Gas (TIG) welding with internal helium backing or high-speed laser welding. The internal gas shielding prevents oxide formation on the bore surface, critical for sanitary applications.
- Solution Annealing: Welded coils undergo solution annealing at 1050–1150 °C in a protective atmosphere (endothermic gas or vacuum) to dissolve any dissolved oxygen, restore full austenitic microstructure, and achieve the required mechanical properties.
- Pickling & Passivation: Post-annealing coils are pickled in a mixed acid solution (nitric + hydrofluoric acid) to remove oxide scale, followed by passivation in a citric or nitric acid solution to establish a stable chromium-rich passive film on the surface.
- Dimensional Inspection & Non-Destructive Testing (NDT): Each coil undergoes ultrasonic thickness testing, hydrostatic pressure testing (per ASTM A270), and eddy current inspection of the weld seam for defect detection.
- Final Packaging & Dispatch: Coils are wrapped in VCI (Vapor Corrosion Inhibitor) paper, placed in export-grade wooden crates or steel containers, and prepared for domestic or international shipment.
5. Applications
The unique combination of ultra-low carbon and molybdenum-bearing chemistry makes 316L coil tube the preferred material for the following critical industries:
5.1 Pharmaceutical & Biotechnology
- CIP (Clean-In-Place) and SIP (Sterilize-In-Place) piping systems requiring repeated autoclaving cycles
- Process lines for aseptic filling, fermentation, and bioreactor connections
- Compliance with FDA 21 CFR Part 117, cGMP, and EU GMP Annex 1 requirements
5.2 Food & Beverage Processing
- Transfer lines for dairy, juice, brewing, and condiment processing
- Equipment housings and sanitary fittings in contact with acidic or salt-containing food products
- Resistance to lactic acid, citric acid, and organic acid environments
5.3 Seawater Desalination (SWRO)
- Feed water piping, concentrate lines, and permeate collection systems
- Resistance to chloride-induced pitting in high-salinity environments (TDS > 35,000 ppm)
- Long-term durability in continuous exposure to seawater without cathodic protection
5.4 High-Purity Water & Ultra-Pure Water (UPW) Systems
- Semi-conductor manufacturing ultrapure water distribution (18.2 MΩ·cm)
- RO (Reverse Osmosis) membrane housing connections and permeate lines
- Low metal ion leaching ensures water purity is maintained
5.5 Additional Applications
- Marine engineering — shipbuilding, offshore platforms, and naval systems
- Chemical processing — handling of dilute mineral acids and reducing agents
- Medical equipment — endoscopes, surgical instrument tubing, and dialysis systems
- Architectural and decorative applications requiring marine-grade durability
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management framework ensuring traceability and conformity to international standards:
- ISO 9001:2015 — Quality Management System certification for consistent manufacturing processes
- ISO 14001:2015 — Environmental Management System for sustainable production practices
- EN 10204 3.1 / 3.2 — Third-party inspection and testing certificates available upon request
- ASTM A270 / A269 — Product conforms to American Society for Testing and Materials specifications for seamless and welded austenitic stainless steel tubing
- EN 10216-5 — European standard for austenitic stainless steel tubes for pressure purposes
- GB/T 12771 / GB/T 13296 — Chinese national standards for stainless steel welded and seamless tubes
- PED 2014/68/EU — Pressure Equipment Directive conformity for pressure-rated applications
- NSF/ANSI 61 — Drinking water system component certification (available for food-grade applications)
- 3-A Sanitary Standards — Compliance with International Dairy, Food & Beverage Sanitary Engineering Standards (for pharmaceutical and food industry applications)
Every shipment is accompanied by a Mill Test Certificate (MTC) detailing chemical composition (by OES spectroscopy), mechanical test results, hydrostatic test pressure, and heat treatment records, ensuring full material traceability from raw steel to finished coil tube.
7. Unique Selling Points
- Superior Corrosion Performance: The synergistic effect of ≤ 0.03 % carbon and 2.0–3.0 % molybdenum provides a PREN of 24–26, offering 2–3× the pitting resistance of standard 304L grade in chloride-rich environments.
- Weldability Without Stabilization: Unlike 316 (standard carbon), the 316L low-carbon variant does not require stabilization heat treatment or stabilizing alloy additions (Ti/Nb), simplifying fabrication and reducing production costs.
- Coil Form Factor Advantage: Continuous coil supply eliminates butt-weld joints in long runs, reducing potential leak points, minimizing installation time, and improving system reliability for sanitary piping.
- Multi-Industry Versatility: A single grade covers pharmaceutical, food, desalination, and high-purity water applications, simplifying procurement and inventory management for OEMs and EPC contractors.
- Full Traceability: End-to-end material certification from steel mill to finished product ensures compliance with the most stringent regulatory requirements in pharma and food industries.
Summary: The 316L Coil Tube from Wenzhou Jixing Metal Materials Co., Ltd represents the optimal balance of corrosion resistance, weldability, mechanical performance, and economic efficiency for demanding process industries. Its low-carbon molybdenum-bearing austenitic structure delivers unmatched protection against pitting, crevice, and intergranular corrosion while maintaining full formability for complex piping layouts.