316L Cold-Drawn Coil Tube for Pressure Gauge & Transmitter Impulse Lines
Product Overview
The 316L Cold-Drawn Coil Tube (Product No. 167) is a precision-engineered stainless steel coiled impulse line specifically designed for pressure measurement instrumentation systems. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this product serves as the critical pressure signal transmission conduit between process instruments and pressure gauges or pressure transmitters in industrial automation environments.
This coil tube is purpose-built to address the dual challenges of vibration-induced fatigue and pulsating pressure dynamics commonly encountered in high-demand process measurement applications. Through advanced material selection, optimized geometric design, and rigorous connection verification protocols, this product delivers superior long-term reliability and measurement integrity.
Material & Properties
Base Material: 316L Cold-Drawn (Seamless) Stainless Steel
The tube is fabricated from AISI 316L (UNS S31603) seamless stainless steel, cold-drawn (重拉) to achieve superior dimensional precision, enhanced mechanical properties, and an exceptionally smooth inner surface finish critical for unimpeded pressure signal transmission.
- Corrosion Resistance: The addition of Molybdenum (2.0–3.0%) provides outstanding resistance to pitting and crevice corrosion, ensuring compatibility with a wide range of process media including chlorinated solutions, acidic environments, and marine atmospheres.
- Low Carbon Grade (L): The "L" designation indicates a maximum carbon content of ≤0.03%, significantly reducing intergranular corrosion susceptibility during welding operations and ensuring structural integrity at connection points.
- Cold-Drawn Advantage: The cold-drawing process (as opposed to hot-rolled or annealed tubing) yields wall thickness tolerances within ±0.02 mm, eliminates surface scale, and imparts a work-hardened microstructure with higher yield strength and fatigue resistance.
- Medium Compatibility: Certified for service with aqueous media, hydrocarbons, food-grade fluids, pharmaceutical solutions, and chemical process streams in accordance with relevant industry standards.
Mechanical Properties (Typical Values for 316L Cold-Drawn)
| Property | Specification | Standard Reference |
|---|---|---|
| Tensile Strength (UTS) | ≥ 550 MPa | ASTM A269 / EN 10217-7 |
| Yield Strength (0.2% Offset) | ≥ 275 MPa | ASTM A269 / EN 10217-7 |
| Elongation (A50mm) | ≥ 35% | ASTM A269 |
| Fatigue Endurance Limit | ≥ 180 MPa (at 10⁷ cycles) | Internal Test Protocol |
| Operating Temperature Range | −196 °C to +450 °C | ASTM A269 |
Specifications
| Parameter | Specification | Notes |
|---|---|---|
| Product Designation | 316L Cold-Drawn Coil Tube (Impulse Line) | Product No. 167 |
| Material Grade | AISI 316L / UNS S31603 (Cold-Drawn) | Seamless, low-carbon grade |
| Tube Outer Diameter (OD) | 3.175 mm (⅛"), 6.35 mm (¼"), 9.525 mm (⅜") | Custom diameters available |
| Wall Thickness | 0.50 mm – 1.50 mm (OD-dependent) | ±0.02 mm tolerance |
| Coil Diameter | Custom per application (typically 15–80 mm) | Determined by installation space |
| Number of Turns | 3 – 12 turns (configurable) | Optimized for vibration damping |
| Connection Type | Ferrule Fitting (DIN 2353 / ASME B16.3) — 卡套连接 | Verified leak-tight to 1.5× rated pressure |
| Designated Pressure Rating | Up to 40 MPa (depending on OD/WT) | Includes pulsation margin |
| Surface Finish | BA (Bright Annealed) or Pickled & Passivated | Ra ≤ 0.4 μm internal |
| Traceability | Full heat-number traceability | Mill certificates provided |
Manufacturing Process
1. Material Selection & Incoming Inspection
Only certified 316L seamless cold-drawn tubing from qualified mills is accepted. Each batch undergoes spectroscopic verification (OES), mechanical testing, and visual inspection to confirm compliance with ASTM A269 / EN 10217-7 requirements prior to fabrication.
2. Precision Forming & Coiling
The tube is cold-formed into a helical coil geometry using CNC-controlled forming equipment. This process maintains metallurgical integrity without heat-affected zone (HAZ) degradation. The coil parameters (diameter, pitch, number of turns) are calculated to provide optimal vibration isolation and pulsation attenuation characteristics for the target application.
3. Vibration-Damping Bend Design (减振弯设计)
A proprietary coil geometry is employed, where the spring-like helical configuration functions as a mechanical vibration damper. Key design principles include:
- The natural frequency of the coil assembly is tuned well below the process vibration frequency to prevent resonance amplification.
- The number of turns and coil diameter are optimized to absorb high-frequency vibration energy through elastic deformation, protecting the pressure sensing element from fatigue.
- For pulsating pressure applications, the coil's compliance provides a mechanical low-pass filter effect, smoothing rapid pressure transients while maintaining signal fidelity within instrument accuracy requirements.
4. Ferrule Connection Assembly & Verification (卡套连接验证)
Both ends of the coil tube are fitted with precision-machined ferrule fittings (DIN 2353 or ASME B16.3 standard). Each assembled unit undergoes rigorous connection verification:
- Torque Verification: Fittings are tightened to specified torque values using calibrated wrenches to ensure proper ferrule deformation and seal formation.
- Leak Testing: Pneumatic or hydraulic pressure testing at 1.5× the maximum operating pressure with helium leak detection (sensitivity ≤ 1×10⁻⁹ mbar·L/s) or soap bubble inspection.
- Cycle Testing: Connection integrity is validated through repeated pressurization/depressurization cycles (minimum 100 cycles) to simulate long-term service conditions.
- Visual Inspection: Ferrule seating and tube end preparation are inspected for proper engagement, absence of scoring, and correct orientation.
5. Final Surface Treatment
Post-fabrication pickling and passivation treatment ensures a chromium-rich passive film on all exposed surfaces, maximizing corrosion resistance and meeting hygienic requirements where applicable.
Applications
This 316L coil tube impulse line is engineered for demanding pressure measurement applications across multiple industrial sectors:
- Oil & Gas Industry: Pressure impulse lines for wellhead gauges, separator pressure transmitters, and pig launcher/launcher receiver instrumentation in environments with vibration from pumps, compressors, and flow-induced oscillations.
- Petrochemical Processing: Connecting pressure transmitters to process vessels, pipelines, and heat exchangers handling aggressive media (chlorides, sulfides) with high pulsation rates.
- Power Generation: Boiler pressure monitoring, steam turbine instrumentation, and nuclear-grade applications requiring vibration isolation and long-term reliability.
- Pharmaceutical & Food Processing: Hygienic-grade impulse lines for CIP/SIP systems where smooth bore surfaces and corrosion resistance are critical.
- Marine & Offshore: Subsea pressure monitoring and deck-mounted instrumentation exposed to continuous mechanical vibration and corrosive marine atmospheres.
- Automotive & Aerospace: High-precision pressure measurement in test benches, hydraulic systems, and engine development facilities.
Unique Selling Points
- Dual-Function Vibration & Pulsation Damping: The optimized coil geometry simultaneously addresses mechanical vibration fatigue and pressure pulsation signal distortion — a combination rarely achieved by rigid impulse lines.
- 316L Cold-Drawn Superiority: Superior dimensional accuracy and mechanical properties compared to standard annealed tubing, ensuring consistent performance and extended service life under cyclic loading.
- Verified Ferrule Integrity: Industry-leading connection verification protocol (leak testing, cycle testing, torque verification) eliminates field failures at connection points — the most common failure mode in impulse line systems.
- Full Medium Compatibility: 316L grade provides exceptional resistance to the widest range of process media without requiring exotic alloy upgrades, offering cost-effective versatility.
Quality Certifications & Standards Compliance
| Standard / Certification | Scope of Compliance |
|---|---|
| ASTM A269 / A270 | Material specification for austenitic stainless steel seamless tube |
| EN 10217-7 | European standard for non-ferrous tubes for pressure purposes |
| DIN 2353 / ASME B16.3 | Ferrule fitting dimensions and connection standards |
| ISO 9001:2015 | Quality Management System certification (manufacturer) |
| EN 10204 Type 3.1 | Inspection certificates per batch |
| ASME B31.3 | Process piping design compliance |
| NACE MR0175 / ISO 15156 | Resistance to sulfide stress cracking (oil & gas service) |
Note: All products are manufactured and inspected in accordance with the company's documented quality procedures. Custom specifications, non-standard coil geometries, and special connection configurations are available upon request. Full material traceability from mill heat number through final product identification is maintained throughout the supply chain.