316L Stainless Steel Coil Tube — Molybdenum Cost Sensitivity & Procurement Specification
Wenzhou Jixing Metal Materials Co., Ltd presents its premium-grade 316L Stainless Steel Coil Tube (also known as Coil Pipe or Coiltube), a high-performance austenitic stainless steel product engineered for demanding industrial, chemical, and pharmaceutical applications. This document provides a comprehensive technical specification with particular emphasis on the critical role of Molybdenum (Mo) as a cost-determinant alloying element and the associated procurement risk management strategies.
Product Overview
The 316L Stainless Steel Coil Tube is a cold-rolled or hot-rolled continuous-length tubing product, supplied in coiled form to maximize material utilization, minimize cutting waste, and facilitate downstream fabrication through automated processing lines. The "L" designation denotes a Low Carbon variant (Carbon ≤ 0.03% maximum), which significantly enhances resistance to intergranular corrosion (IGC) following welding operations.
Coil tube products are distinguished from straight-length (cut-length) tubes by their continuous winding configuration, which enables seamless feeding into bending, forming, and machining operations without joint discontinuities. This form factor is particularly advantageous in high-volume manufacturing environments where material efficiency and production throughput are paramount.
Unique Selling Points
- Superior Corrosion Resistance: Molybdenum addition (2.0%–3.0%) provides exceptional resistance to pitting and crevice corrosion in chloride-containing environments, including marine atmospheres, chemical processing, and pharmaceutical sterilization cycles.
- Low Carbon Advantage: The ultra-low carbon content (≤ 0.03% C) eliminates the risk of chromium carbide precipitation at grain boundaries, ensuring long-term structural integrity in welded assemblies.
- Coil Form Efficiency: Continuous coil supply reduces material waste by up to 15%–25% compared to cut-length equivalents, directly translating to cost savings in high-volume production.
- Procurement Risk Management: Wenzhou Jixing Metal Materials Co., Ltd implements dynamic pricing mechanisms and shortened price-locking cycles to mitigate the financial risk associated with Molybdenum market volatility.
Material & Properties
Chemical Composition (ASTM A270 / EN 10216-5 Standard)
| Element | Symbol | Composition Range (%) | Functional Role |
|---|---|---|---|
| Carbon | C | ≤ 0.030 | Low carbon content prevents intergranular corrosion |
| Chromium | Cr | 16.50 – 18.50 | Primary passive layer former; corrosion resistance |
| Nickel | Ni | 10.00 – 14.00 | Austenite stabilizer; ductility and toughness |
| Molybdenum | Mo | 2.00 – 3.00 | Enhanced pitting/crevice corrosion resistance; key cost driver (15%–20% of 316L cost) |
| Manganese | Mn | ≤ 2.00 | Deoxidizer; minor strength contribution |
| Silicon | Si | ≤ 1.00 | Deoxidizer; fluidity improvement |
| Phosphorus | P | ≤ 0.045 | Impurity limit |
| Sulfur | S | ≤ 0.030 | Impurity limit |
| Iron | Fe | Balance | Base matrix element |
Mechanical Properties (Annealed Condition)
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (UTS) | ≥ 485 MPa (70,300 psi) | ASTM A270 / EN 10216-5 |
| Yield Strength (0.2% Offset) | ≥ 170 MPa (24,650 psi) | ASTM A270 / EN 10216-5 |
| Elongation at Break | ≥ 40% (in 50 mm / 2 in gauge length) | ASTM A270 |
| Hardness (Brinell) | ≤ 210 HB | ASTM A270 |
| Density | 7.98 g/cm³ | — |
| Thermal Conductivity (at 100°C) | 16.3 W/(m·K) | — |
| Specific Heat Capacity | 500 J/(kg·K) | — |
| Electrical Resistivity (at 20°C) | 0.00074 Ω·m | — |
| Maximum Service Temperature | 870°C (1598°F) | — |
Corrosion Resistance Characteristics
- Pitting Resistance: Molybdenum content of 2.0%–3.0% provides a Critical Pitting Temperature (CPT) of approximately 30°C–40°C in 3% NaCl solution at pH 3.5, substantially exceeding the CPT of 304L (~5°C).
- Crevice Corrosion: Enhanced resistance in tight geometric configurations where oxygen depletion occurs, critical for gasketed joints and bolted connections.
- Intergranular Corrosion (IGC): Passes ASTM A262 Practice E (65% boiling H₂SO₄ + HNO₃) test without grain boundary attack, verified by the ≤ 0.03% carbon content.
- Stress Corrosion Cracking (SCC): Moderate resistance in warm chloride environments; recommended for service temperatures below 60°C in concentrated chloride solutions.
- Acid Resistance: Excellent performance in dilute sulfuric, phosphoric, and acetic acids; moderate resistance to dilute hydrochloric acid (HCl) below 20°C.
Specifications
Dimensional Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 219.0 mm (1/4" – 8-5/8") | ASTM A270 / EN 10216-5 |
| Wall Thickness (WT) | 0.5 mm – 12.0 mm (0.020" – 0.472") | ASTM A270 / EN 10216-5 |
| OD Tolerance | ±0.10 mm to ±0.50 mm (depending on size) | EN 10216-5 |
| Wall Thickness Tolerance | ±10% (standard); ±5% (close tolerance) | EN 10216-5 |
| Coil Length | Customized; typically 1,000 m – 5,000 m per coil | Supplier Specification |
| Coil Inner Diameter (ID) | 300 mm – 600 mm (standard options) | Supplier Specification |
| Surface Finish | 2B (Cold Rolled & Annealed), BA (Bright Annealed), No. 4 Brushed, Mirror (No. 8) | ASTM A480 / EN 10088-2 |
| Surface Roughness (Ra) | 2B: ≤ 0.5 μm; BA: ≤ 0.4 μm; Mirror: ≤ 0.05 μm | Supplier Specification |
| End Condition | Plain, Beveled, Threaded, or Custom | Customer Requirement |
Applicable Standards & Norms
| Standard | Designation | Description |
|---|---|---|
| ASTM A270 / A270M | 316L | Standard Specification for Seamless and Welded Austenitic Stainless Steel Pipes, Tubes, and Shapes for Chemical and Similar Severe Service Applications |
| EN 10216-5 | X2CrNiMo17-12-2 | Technical delivery conditions for seamless and welded tubes for pressure purposes — Austenitic and austenitic-ferritic stainless steel tubes |
| ISO 3506 | 316L | Stainless steel — Technical delivery conditions for fasteners — General requirements for cold worked fasteners of austenitic and austenitic-ferritic stainless steels |
| JIS G3446 | SUS316L | Stainless steel tubes for general use |
| GB/T 12771 | 06Cr17Ni12Mo2 | Stainless steel seamless tubes for general purposes (Chinese National Standard) |
Manufacturing Process
Production Workflow
- Raw Material Procurement & Ingot Casting: High-purity Molybdenum (Mo), Chromium (Cr), and Nickel (Ni) alloying elements are combined with molten steel in an Electric Arc Furnace (EAF) or Vacuum Arc Remelting (VAR) process. The molten steel is cast into ingots or continuously cast into slabs. Molybdenum content is precisely controlled at 2.0%–3.0% to ensure optimal corrosion resistance while managing cost exposure.
- Hot Rolling: Slabs are reheated to 1,100°C–1,200°C and hot-rolled into seamless tube billets or hot-rolled coil stock. This step establishes the initial dimensions and breaks up the cast structure.
- Piercing & Pipe Forming: For seamless tubes, the hot billet is pierced to create a hollow shape, then drawn over a mandrel or rolled through a plug mill to achieve the target inner diameter (ID).
- Cold Drawing / Cold Rolling: The hot-rolled tube is cold-drawn or cold-rolled to achieve precise dimensional tolerances (±5%–10% on wall thickness) and improved mechanical properties. Cold working increases yield strength by 30%–50% compared to the annealed condition.
- Intermediate Annealing: Periodic solution annealing at 1,050°C–1,100°C in controlled atmosphere (protective gas or vacuum) relieves cold work stresses, restores full ductility, and dissolves any precipitated carbides to maintain corrosion resistance.
- Pickling & Passivation: The tube surface is cleaned using a mixed acid bath (typically HNO₃ + HF or HNO₃ + HCl) to remove scale, oxide, and surface contaminants. A final passivation treatment with nitric acid (HNO₃ 20%–30%) establishes a stable chromium oxide passive film (Cr₂O₃) for optimal corrosion resistance.
- Final Annealing & Surface Treatment: A final bright annealing (BA) cycle in a reducing atmosphere (H₂/N₂ mix or controlled carbon potential) produces a clean, oxide-free surface suitable for high-purity applications. Alternative surface finishes (2B, brushed, mirror) are applied as specified.
- Coiling & Packaging: The finished tube is wound onto a coil mandrel at controlled tension to prevent deformation. Coils are wrapped in protective plastic film, placed on wooden or steel pallets, and secured for transport. Each coil is labeled with heat number, dimensions, grade, and certification reference.
- Quality Inspection & Certification: Each coil undergoes comprehensive non-destructive testing (NDT) including eddy current inspection (ECI) for internal and external defects, hydrostatic pressure testing