316L Stainless Steel Coil Tube (Coiltube) — Technical Product Specification
1. Product Overview
The 316L Stainless Steel Coil Tube (also referred to as Coiltube or Coil Tube) is a precision-engineered austenitic stainless steel tubing product supplied in continuous coil configuration. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this product is designed to meet the demanding requirements of industrial piping systems, heat exchanger assemblies, chemical processing equipment, and high-integrity containment applications where corrosion resistance, mechanical integrity, and leak-tight performance are paramount.
Unlike straight-length tubes, coil tubes are formed in a continuous helical winding, enabling high-efficiency downstream processing, automated cutting, and minimal material waste. The 316L grade designation indicates the low-carbon variant of AISI 316 stainless steel, specifically engineered to mitigate sensitization and intergranular corrosion risks during welding and high-temperature service.
2. Material Composition & Mechanical Properties
2.1 Chemical Composition (ASTM A213 / A269 / ASME SA-213)
| Element | Specification Range (%) | Notes |
|---|---|---|
| Carbon (C) | ≤ 0.030 | Ultra-low carbon content prevents chromium carbide precipitation |
| Manganese (Mn) | ≤ 2.00 | — |
| Silicon (Si) | ≤ 1.00 | — |
| Chromium (Cr) | 16.00 – 18.00 | Primary corrosion-resistant alloying element |
| Nickel (Ni) | 10.00 – 14.00 | Stabilizes austenitic microstructure |
| Molybdenum (Mo) | 2.00 – 3.00 | Enhances pitting and crevice corrosion resistance |
| Phosphorus (P) | ≤ 0.045 | — |
| Sulfur (S) | ≤ 0.030 | — |
| Nitrogen (N) | ≤ 0.10 | — |
| Iron (Fe) | Balance | — |
2.2 Mechanical Properties (Annealed Condition)
| Property | Specification Value | Test Method |
|---|---|---|
| Tensile Strength (UTS) | ≥ 485 MPa (70 ksi) | ASTM A370 |
| Yield Strength (0.2% Offset) | ≥ 170 MPa (25 ksi) | ASTM A370 |
| Elongation (in 50 mm / 2 in) | ≥ 40% | ASTM A370 |
| Hardness (Rockwell B) | ≤ 95 HRB | ASTM A38 |
| Thermal Conductivity (at 100°C) | ≈ 16.3 W/(m·K) | — |
| Electrical Resistivity (at 20°C) | ≈ 0.74 μΩ·m | — |
| Modulus of Elasticity | ≈ 193 GPa (28 × 10⁶ psi) | — |
| Maximum Service Temperature | 870°C (1598°F) [in air] | — |
2.3 Corrosion Resistance Characteristics
The addition of 2.00–3.00% Molybdenum (Mo) to the 316L alloy provides significantly enhanced resistance to pitting corrosion, crevice corrosion, and intergranular corrosion compared to standard 304L stainless steel. The ultra-low carbon content (≤ 0.030%) ensures that the material maintains full corrosion resistance even after welding, as it eliminates the formation of chromium carbide precipitates at the grain boundaries (sensitization) in the temperature range of 425°C to 870°C (800°F to 1598°F).
3. Product Specifications
| Parameter | Specification | Reference Standard |
|---|---|---|
| Material Grade | 316L (UNS S31603) | ASTM A213 / A269 / ASME SA-213 / SA-269 |
| Product Form | Seamless or Welded Coil Tube | — |
| Outer Diameter (OD) | 6.0 mm – 108.0 mm (¼" – 4") | ASTM A511 / EN 10217 |
| Wall Thickness | 0.5 mm – 6.0 mm (0.020" – 0.236") | ASTM A511 / EN 10217 |
| Coil Length | Customizable; typically 50 m – 500 m per coil | — |
| Coil Weight | Up to 5,000 kg (11,000 lbs) per coil | — |
| Surface Finish | Pickled & Passivated (P&P), Mill Finish, or Custom | ASTM A967 |
| Surface Roughness (Ra) | 0.5 – 1.6 μm (Standard P&P) | ASTM A967 / EN ISO 16232 |
| Roundness Tolerance | ± 0.5% of OD | ASTM A511 |
| OD Tolerance | ± 0.05 mm (± 0.002") | ASTM A511 / EN 10217 |
| Wall Thickness Tolerance | ± 10% of nominal | ASTM A511 / EN 10217 |
| Hardness (Annealed) | ≤ 95 HRB | ASTM A38 |
| Heat Treatment Condition | Solution Annealed (1050°C – 1150°C), followed by air or water quench | ASTM A999 |
| Welding Suitability | Excellent — suitable for TIG (GTAW), MIG (GMAW), SAW, and resistance welding | ASME Section IX |
| Non-Destructive Testing (NDT) | Eddy Current (ET), Ultrasonic (UT), Hydrostatic Testing | ASTM A999 / ASME BPV Code |
| Packaging | Export-grade wooden crates or steel bands with moisture-proof wrapping | ISO 4180 |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Selection: High-purity 316L stainless steel billet or strip is sourced from certified steel mills. Incoming material undergoes spectroscopic analysis (OES) to verify chemical composition compliance with ASTM/EN specifications.
- Hot Rolling: The steel billet is heated to approximately 1200°C – 1300°C and hot-rolled into seamless tube blanks or hot-rolled strip for welded tube production.
- Piercing & Enlarging (Seamless Route): Hot-rolled blanks are pierced using Mannesmann or plug piercing mills, then further elongated through multiple passes on elongation mills to achieve the desired OD and wall thickness.
- Cold Drawing / Cold Rolling: Tubes are cold-drawn through precision-die sets or cold-rolled on spiral mills to achieve tight dimensional tolerances, improved mechanical properties, and superior surface finish. This process work-hardens the material, which is subsequently relieved by annealing.
- Heat Treatment (Solution Annealing): Tubes are heated to 1050°C – 1150°C in a controlled-atmosphere furnace (inert or vacuum) and rapidly quenched to restore full austenitic microstructure and maximum corrosion resistance.
- Pickling & Passivation: Tubes are immersed in a citric acid or nitric-hydrofluoric acid bath to remove mill scale, oxide films, and surface contaminants, followed by passivation to establish a stable, protective chromium oxide layer (Cr₂O₃) on the surface.
- Coil Winding: Processed tube is wound into coils of specified diameter and length using automated coiling machines. Coil dimensions are controlled to ensure uniform tension and prevent mechanical damage.
- Quality Inspection & Testing: Every coil undergoes comprehensive inspection including dimensional measurement, chemical analysis, mechanical testing (tensile, hardness), and non-destructive testing (eddy current and ultrasonic examination).
- Packaging & Dispatch: Inspected coils are wrapped in moisture-proof film, secured with steel strapping, and loaded into export-grade wooden crates for safe transportation.
4.2 Critical Process Controls for Leak Prevention
Based on extensive failure analysis studies of 316L coil tubes in service, the following process controls are implemented to prevent leakage failures:
- Wall Thickness Uniformity: Continuous online monitoring ensures wall thickness variation remains within ± 10% of nominal, preventing thin-wall regions susceptible to erosion-corrosion or stress corrosion cracking (SCC).
- Seam Integrity (Welded Tubes): Eddy current testing is performed at a minimum of 100% coverage to detect longitudinal and transverse seam defects, including porosity, lack of fusion, and cracks.
- Hydrostatic Testing: Each tube length is subjected to hydrostatic pressure testing at 1.5 × the maximum allowable working pressure (MAWP) to verify leak-tight integrity.
- Surface Defect Elimination: Post-pickling inspection identifies and rectifies surface defects such as laps, tears, and inclusions that could serve as initiation sites for localized corrosion.
5. Applications
5.1 Primary Application Domains
- Petrochemical & Chemical Processing: Piping systems for handling aggressive chemicals, acids (including sulfuric, hydrochloric, and phosphoric acids), and caustic solutions where Mo-enhanced corrosion resistance is critical.
- Food & Beverage Processing: Sanitary-grade tubing for dairy, brewing, and pharmaceutical processing lines requiring non-reactive, easily cleanable surfaces.
- Marine & Offshore Engineering: Ballast water systems, seawater cooling circuits, and structural components exposed to chloride-rich environments.
- Heat Exchangers & Condensers: Tubular bundles in shell-and-tube heat exchangers, condensers, and evaporators operating in corrosive process streams.
- Power Generation: Boiler tubes, superheater tubes, and auxiliary systems in fossil fuel, nuclear, and renewable energy plants.
- Automotive & Aerospace: Exhaust system components, fuel lines, and hydraulic tubing requiring high-temperature and corrosion resistance.
- Medical & Pharmaceutical: Cleanroom piping, sterilization equipment, and instrument tubing in GMP-regulated environments.
- Oil & Gas: Downhole tubing, wellhead components, and offshore platform piping systems.
5.2 Unique Selling Points
1. Superior Leak Resistance: Wenzhou Jixing Metal Materials Co., Ltd. applies rigorous process controls derived from systematic leakage failure analysis of 316L coil tubes, including 100% eddy current inspection, hydrostatic testing, and wall thickness uniformity monitoring. This results in a demonstrably lower field failure rate compared to industry averages.
2. Ultra-Low Carbon Assurance: The ≤ 0.030% carbon specification ensures that the tubing maintains full intergranular corrosion resistance even after welding, eliminating the need for post-weld solution treatment in most applications.
3. Custom Coil Configuration: Flexible coil length, OD, and wall thickness customization enables optimized downstream fabrication, reduced material waste