316L Cold-Drawn Stainless Steel Coil Impulse Tube for Pressure Measurement Instruments
Product Overview
This precision-engineered stainless steel coil impulse tube is specifically designed for use in pressure gauge and pressure transmitter signal transmission lines within industrial instrumentation systems. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this coil tube is purpose-built to withstand the demanding conditions of vibration and pulsating pressure environments commonly encountered in process control, oil & gas, chemical processing, and power generation applications. The product combines superior material integrity, intelligent mechanical design, and rigorous connection verification to deliver reliable pressure signal transmission over extended service life.
Material & Properties
The impulse tube is fabricated from 316L cold-drawn (re-drawn) seamless stainless steel, selected for its exceptional combination of mechanical strength, corrosion resistance, and fatigue durability. The cold-drawing process significantly enhances the tube's surface finish, dimensional accuracy, and fatigue resistance compared to standard cold-rolled or hot-rolled alternatives.
- Grade: 316L (UNS S31603 / EN 1.4404)
- Molybdenum Content: 2.0–2.5% — provides superior resistance to pitting and crevice corrosion in chloride-containing media
- Low Carbon: ≤0.03% — eliminates intergranular corrosion risk during welding or exposure to elevated temperatures
- Tensile Strength: ≥515 MPa (cold-drawn condition)
- Yield Strength: ≥205 MPa
- Surface Finish: Ra ≤ 0.4 μm (internal), Ra ≤ 0.8 μm (external)
- Temperature Range: -196 °C to +425 °C (continuous service)
Key Specifications
| Parameter | Specification |
|---|---|
| Material | 316L Cold-Drawn Seamless Stainless Steel |
| Outer Diameter (OD) | 3.0 mm / 6.0 mm / 8.0 mm / 10.0 mm (customizable) |
| Wall Thickness | 0.5 mm – 1.5 mm (per ASME B36.19M) |
| Coil Diameter | 32 mm / 50 mm / 75 mm / 100 mm (standard); custom upon request |
| Tube Length (Coiled) | 1 m – 10 m per coil; cut-to-length available |
| Connection Type | Compression Ferrule (DIN EN ISO 8434-2 / SAE J1926-3) |
| Pressure Rating | Up to 40 MPa (400 bar) — verified per connection assembly |
| Maximum Pulsating Pressure | 20 MPa sustained; 40 MPa transient (peak-to-peak ≤ 10 MPa) |
| Vibration Resistance | 10 g RMS, 5–2000 Hz (per IEC 60068-2-64) |
| End Treatment | Deburred, chamfered (30°–45°), passivated |
| Standard | ASTM A269 / ASTM A213 / EN 10216-5 / GB/T 12771 |
Manufacturing Process
1. Raw Material Selection & Cold Drawing
Starting from certified 316L seamless pipe (hot-finished or cold-finished per ASTM A213 TP316L), the tube undergoes multiple passes of cold drawing (re-drawing) through precision tungsten carbide dies. This multi-stage cold working process refines the grain structure, eliminates residual defects from hot rolling, and achieves the tight dimensional tolerances (±0.05 mm on OD, ±0.02 mm on wall thickness) required for reliable ferrule connection assembly.
2. Vibration-Damping Bend Design (Anti-Vibration Loop)
The coil tube incorporates a purpose-engineered vibration-damping bend (snubber loop) geometry. This design strategically introduces controlled-radius bends that absorb and dissipate kinetic energy from mechanical vibration and pressure pulsation before it reaches the delicate pressure gauge or transmitter diaphragm. The bend radius is calculated to maintain a minimum of 6× tube OD, preventing kinking while maximizing energy dissipation. This reduces instrument fatigue, extends gauge life by up to 300%, and minimizes measurement drift under dynamic conditions.
3. Ferrule Connection Verification & Testing
Every coil tube assembly undergoes 100% ferrule connection verification prior to shipment. This includes:
- Hydraulic pressure testing to 1.5× rated pressure (minimum 60 MPa) with 5-minute hold
- Helium leak detection at 1×10⁻⁹ Pa·m³/s sensitivity
- Visual and dimensional inspection of ferrule seating and tube end preparation
- Cycle testing: 10,000 pressure cycles from 0 to rated pressure with no leakage or dimensional change
4. Surface Treatment & Passivation
Following fabrication, all tubes undergo nitric acid passivation (ASTM A967) to remove surface iron contamination and restore the protective chromium oxide layer. This ensures long-term corrosion resistance and compatibility with aggressive process media.
Applications
- Pressure Gauge Impulse Lines: Connecting process piping to bourdon tube, digital, or capsule pressure gauges in high-vibration environments
- Pressure Transmitter Signal Tubing: Impulse lines from process isolation valves to 4–20 mA / HART / Fieldbus pressure transmitters
- Oil & Gas Downhole Monitoring: Wellhead pressure measurement with resistance to H₂S, CO₂, and high pulsation
- Chemical Processing: Corrosive medium pressure measurement (acids, alkalis, chlorides)
- Petrochemical Refining: Crude oil fractionation units, hydrotreating, and catalytic cracking pressure monitoring
- Power Generation: Steam pressure measurement in boilers, turbines, and feedwater systems
- Automotive & Aerospace Test Rigs: High-cycle pressure measurement in dynamic test environments
Unique Selling Points
- Integrated Anti-Vibration Design: Proprietary damping bend geometry eliminates the need for separate snubbers, reducing installation complexity and failure points
- 316L Cold-Drawn Superiority: 40% higher fatigue life than standard 304 coil tube; superior resistance to chloride pitting
- 100% Connection Verification: Every unit is pressure-tested and leak-checked — zero compromise on reliability
- Full Media Compatibility: Suitable for hydrocarbon, aqueous, gaseous, and chemical media including H₂S, CO₂, and dilute acids
- Customizable Geometry: Coil diameter, tube length, and connection type tailored to specific instrument mounting configurations
Quality Certifications & Standards Compliance
- Material Certification: EN 10204 Type 3.1 mill certificates with full chemical and mechanical analysis
- Manufacturing Standard: ISO 9001:2015 certified production facility
- Product Standards: ASTM A269, ASTM A213, EN 10216-5, GB/T 12771
- Connection Standard: DIN EN ISO 8434-2 / SAE J1926-3 / GB/T 3453.2
- Pressure Testing: Per ASME B31.3 / PED 2014/68/EU (Cat. II, where applicable)
- Third-Party Inspection: Available — SGS, TÜV, or customer-designated NDT inspection
- Traceability: Full heat number traceability from raw material to finished product
Ordering Information
Wenzhou Jixing Metal Materials Co., Ltd. offers this 316L coil impulse tube in standard configurations and fully customized specifications. Contact our engineering team to specify required tube OD, wall thickness, coil diameter, connection type, total length, and media compatibility requirements. Sample units and custom prototyping are available for application validation prior to bulk procurement.