316L Cold-Drawn Stainless Steel Coiltube for Pressure Gauge/Transmitter Impulse Lines
1. Product Overview
The 316L Cold-Drawn Stainless Steel Coiltube (Product No. 167) is a precision-engineered impulse tubing solution designed specifically for pressure measurement instrumentation systems. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this coiltube serves as the critical connecting element between process media and pressure gauges or pressure transmitters in industrial instrumentation applications.
This product addresses two primary engineering challenges inherent to pressure measurement systems: vibration-induced fatigue and pulsating pressure dynamics. Through a proprietary vibration-damping bend design and the use of 316L cold-drawn tubing material, this coiltube ensures reliable, long-term pressure signal transmission integrity even in demanding industrial environments characterized by mechanical vibration and rapid pressure fluctuations.
2. Material & Properties
2.1 Base Material: 316L Cold-Drawn Tube
The tube is fabricated from SUS 316L (UNS S31603) austenitic stainless steel, cold-drawn to achieve superior mechanical properties and dimensional accuracy. The "L" designation indicates a low-carbon variant (C ≤ 0.03%), which significantly enhances resistance to sensitization and intergranular corrosion during welding operations.
Key Material Characteristics:
- Chromium (Cr): 16.0–18.0% — provides primary corrosion resistance
- Nickel (Ni): 10.0–14.0% — stabilizes austenitic microstructure
- Molybdenum (Mo): 2.0–3.0% — enhances resistance to pitting and crevice corrosion
- Carbon (C): ≤ 0.03% — minimizes sensitization risk
2.2 Medium Compatibility
The 316L cold-drawn material demonstrates exceptional compatibility with a wide range of process media, including:
- Acidic and alkaline aqueous solutions
- Chloride-containing environments (resistant to pitting up to moderate Cl⁻ concentrations)
- Organic solvents and hydrocarbons
- Steam and high-temperature gases
- Food-grade and pharmaceutical process fluids
- Chemical processing media (acids, alkalis, salts)
2.3 Mechanical Properties (Typical)
- Tensile Strength: ≥ 515 MPa (75 ksi)
- Yield Strength: ≥ 205 MPa (30 ksi)
- Elongation: ≥ 40%
- Hardness: ≤ 217 HB (cold-drawn condition)
3. Technical Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Material Grade | 316L (UNS S31603) Cold-Drawn | ASTM A269 / ASTM A213 |
| Tube Type | Seamless Coiltube (Impulse Tube) | ASME B36.19M |
| Outer Diameter (OD) | Available in 3.18 mm (1/8"), 6.35 mm (1/4"), 9.53 mm (3/8"), 12.7 mm (1/2") | — |
| Wall Thickness | 0.50 mm – 1.65 mm (varies by OD) | — |
| Coil Length | Customizable (typically 50 mm – 200 mm working length) | — |
| Surface Finish | Mirror Polish (Ra ≤ 0.25 μm) or Industrial Polish (Ra ≤ 0.5 μm) | — |
| Connection Type | Compression Fitting (Swagelok-compatible) / Threaded (G, NPT, BSP) | ASME B1.20.1 |
| Pressure Rating | Up to 40 MPa (5,800 psi) at 25°C | ASME B31.3 |
| Temperature Range | −196°C to +450°C | — |
| Vibration Damping | Integrated vibration-damping bend design (minimum 2 loops) | Proprietary |
| Pulsation Resistance | Validated for rapid pressure cycling (≥ 10⁶ cycles fatigue endurance) | — |
| Compliance | ISO 9001, PED 2014/68/EU, CE Marked | — |
4. Manufacturing Process
4.1 Cold Drawing
The base tube is produced through a multi-pass cold-drawing process, which imparts superior mechanical properties compared to hot-rolled alternatives. Cold drawing refines the grain structure, enhances dimensional precision (tolerance within ±0.05 mm for OD), and produces a smooth internal bore that minimizes fluid turbulence and pressure signal distortion.
4.2 Vibration-Damping Bend Design
A proprietary coil geometry is formed through precision bending operations. The vibration-damping bend design incorporates carefully calculated loop configurations that serve as mechanical low-pass filters, effectively attenuating high-frequency vibrations transmitted from the process equipment. This design prevents:
- Fatigue cracking at tube-to-fitting junctions
- Pressure signal oscillation (damping of pressure pulsations)
- Connector loosening due to dynamic loading
4.3 Compression Fitting Integration & Verification
Each coiltube assembly undergoes rigorous compression fitting verification. The connection interface is validated through:
- Dimensional inspection of fitting components (olive, nut, body)
- Pressure tightness testing (hydrostatic test at 1.5× working pressure)
- Cycle fatigue testing to verify seal integrity under vibration conditions
- Visual and dye-penetrant inspection of joint surfaces
4.4 Surface Finishing
The final surface treatment includes mechanical polishing followed by passivation (nitric acid or citric acid passivation per ASTM A967), ensuring optimal corrosion resistance and a hygienic surface suitable for pharmaceutical and food applications.
5. Applications
5.1 Primary Application: Pressure Gauge/Transmitter Impulse Lines
This coiltube is specifically engineered for use as impulse tubing in pressure measurement systems, connecting process vessels or pipelines to:
- Analog and digital pressure gauges
- Pressure transmitters (4–20 mA, HART, Foundation Fieldbus)
- Pressure switches and limiters
- Flow measurement systems (differential pressure elements)
5.2 Typical Industrial Sectors
- Petrochemical & Refining: Crude oil processing, catalytic cracking units, hydrogen service
- Pharmaceutical & Biotechnology: CIP/SIP systems, bioreactor pressure monitoring
- Food & Beverage: Hygienic processing lines, pasteurization systems
- Power Generation: Steam systems, boiler pressure monitoring
- Chemical Processing: Acid/alkali handling, reactor pressure control
- Oil & Gas: Upstream/downstream pressure instrumentation
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality management and product certification programs:
| Certification / Standard | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System |
| PED 2014/68/EU (Category II/III) | Pressure Equipment Directive — CE Conformity |
| ASME BPV Code (U Stamp) | Pressure Vessel & Piping Components |
| EN 10204 3.1 | Material Test Certification |
| NACE MR0175 / ISO 15156 | Sour Service (H₂S) Compliance |
| 3-A Sanitary Standards | Food & Dairy Hygiene |
| EHEDG | European Hygienic Engineering & Design Group |
7. Unique Selling Points
1. Proprietary Vibration-Damping Bend Geometry — Unlike conventional straight impulse tubes, the coiltube's integrated loop design provides inherent mechanical vibration isolation, reducing fatigue failure rates by up to 90% in high-vibration environments.
2. 316L Cold-Drawn Superiority — Cold-drawn 316L offers 20–30% higher fatigue endurance limit compared to hot-rolled equivalents, ensuring extended service life under pulsating pressure conditions (validated for ≥ 10⁶ pressure cycles).
3. Verified Compression Fitting Integrity — Each assembly undergoes full compression fitting verification including fatigue cycling and pressure tightness testing, guaranteeing leak-free connections throughout the service life.
4. Comprehensive Medium Compatibility — The 316L low-carbon austenitic composition provides broad chemical resistance, eliminating the need for special alloys in most process environments and reducing total cost of ownership.
5. Customizable Coil Geometry — Coil length, loop configuration, and connection types are customizable to meet specific installation constraints and vibration attenuation requirements.