Rosemount™ 3418 Eight-Path Gas Ultrasonic Flow Meter for Fiscal Measurement
Summary: The Rosemount™ 3418 Eight-Path Gas Ultrasonic Flow Meter is engineered specifically for high-stakes custody transfer and fiscal natural gas measurement. By utilizing a patented dual-interlocked, mirror-image chordal path layout, the 3418 automatically cancels out complex swirl and asymmetrical velocity profiles caused by upstream piping disturbers. It achieves exceptional OIML Class 0.5 accuracy (±0.1%) while requiring only 5 diameters (5D) of upstream straight pipe run and zero flow conditioners. This design eliminates permanent pressure drop, lowers compression energy costs, and reduces installation footprint for natural gas transmission, city gates, and large industrial gas headers.
⚡ Quick Answer: Why Choose the Rosemount 3418 for Fiscal Gas Measurement?
The Rosemount 3418 resolves the biggest pain point in fiscal gas metering: achieving high precision in tight spaces without permanent pressure loss.
- Precision Accuracy: Delivers ±0.1% accuracy (OIML R137 Class 0.5 compliant) over a wide >100:1 turndown envelope.
- Space Savings: Requires only 5D upstream straight run without any flow conditioning plates.
- Zero Pressure Loss: Full-bore design removes line restriction, significantly cutting compressor fuel/power consumption (OPEX).
- Hot-Tapped Maintenance: Titanium T-200 transducers can be safely extracted under line pressure without shutting down gas flow.
- Estimated Price Range: $15,000.00 – $65,000.00 USD (Depending on pipe size, flange rating, and certification options).
📌 What You Will Learn in This Engineering Guide (Overview)
✔ Technical Specifications: Key engineering limits & ratings.
✔ Technology Comparison: 3418 vs. 3417 vs. Turbine/Orifice.
✔ Selection Decision Tree: Logic flow for choosing gas meters.
✔ Pros, Cons & Limits: Honest engineering trade-offs.
✔ EPC Procurement Checklist: Crucial retrofitting parameters.
✔ Purchasing FAQ: Answers to common engineering questions.
1. Technical Specifications Summary
Below are the essential operational parameters and commercial pricing guide for the Rosemount 3418 ultrasonic flow meter:
| Specification Parameter |
Rosemount 3418 Performance Envelope |
| Line Sizes |
DN250 to DN1050 (10-inch to 42-inch) |
| Accuracy Class |
±0.1% of reading (OIML R137 Class 0.5 compliant) |
| Repeatability |
±0.05% of reading (velocity range 1.5 to 30.5 m/s) |
| Path Configuration |
8-Path (Dual Interlocked Mirror-Image British Gas Layout) |
| Piping Requirements |
5D Upstream / 3D Downstream (Zero Flow Conditioner Needed) |
| Max Operating Pressure |
Up to 27,579 kPag (4,000 psig) / ASME Class 150 to 1500 |
| Transducer Technology |
T-200 Titanium Encapsulated (Extractable under pressure up to 42") |
| Turndown Envelope |
>100:1 operational rangeability |
2. Technology Comparison Matrix
Evaluating technology options for fiscal natural gas measurement? Here is how the Rosemount 3418 compares against alternative flow measurement solutions:
| Feature / Metric |
Rosemount 3418 (8-Path) |
Rosemount 3417 (4+4 Redundant) |
Orifice Plate |
Gas Turbine Meter |
| Primary Application |
Fiscal / Custody Transfer (Compact Space) |
Fiscal Measurement (Dual Redundancy) |
Standard Gas Allocation |
Medium-Accuracy Gas Measurement |
| Accuracy |
±0.1% |
±0.15% |
±1.0% to ±2.0% |
±0.5% to ±1.0% |
| Straight Run Required |
5D (No Conditioner) |
10D (With Conditioner) |
10D - 30D (With Plate) |
10D - 20D |
| Permanent Pressure Loss |
Zero |
Minimal (from conditioner) |
High |
Moderate |
| Moving Parts / Wear |
None |
None |
Edge Wear / Erosion |
High (Rotor Bearings) |
3. Gas Ultrasonic Flow Meter Selection Decision Tree
Follow this visual logic tree to determine if the Rosemount 3418 is the correct engineering selection for your gas metering pipeline:
START: High-Volume Gas Measurement Project│
├──►
Is it for Custody Transfer / Fiscal Billing (OIML Class 0.5)?│ ├──
NO: Consider standard industrial ultrasonic or vortex flowmeters.
│ └──
YES: Proceed to piping layout audit.
│
├──►
Is upstream piping constrained (e.g., < 10D straight run available)?│ ├──
YES: ➔
SELECT ROSEMOUNT 3418 (8-Path Mirror Design, 5D Run, No Conditioner)│ └──
NO: Evaluate redundancy requirements.
│
└──►
Do you require two completely independent measurement systems in one body?├──
YES: ➔
Select Rosemount 3417 (4+4 Dual-Configuration)└──
NO: ➔
SELECT ROSEMOUNT 3418 (Maximum Swirl Cancellation & Lowest Footprint)
4. Engineering Pros, Cons & Limitations
✅ Key Advantages (Pros)
- Patented Mirror-Image Layout: Automatically cancels swirl and cross-flow without requiring flow-straightening plates.
- Lowest TCO: Zero restriction means zero head loss, saving hundreds of thousands in long-term compressor fuel costs.
- Online Maintenance: T-200 titanium transducers can be extracted under pressure without shutting down gas flow.
- Advanced Verification: Built-in 3410 Series electronics feature Smart Meter Verification for continuous self-diagnostics.
❌ Limitations & Considerations (Cons)
- Higher Initial CAPEX: Higher upfront investment ($15,000+) compared to traditional orifice or turbine meters.
- Clean Gas Requirement: Best suited for dry, clean natural gas; heavy liquids/slurries require alternative meters like Rosemount 9195 Wedge Flow Meters.
- Pipe Size Restriction: Minimum line size starts at DN250 (10-inch). Not available for small lines under 10".
5. Real-World Procurement & Field Retrofit Checklist
From our engineering team's experience: If you are purchasing the Rosemount 3418 to replace existing turbine, orifice, or older ultrasonic meters, you must verify these 6 technical points before issuing a Purchase Order (PO):
📋 Pre-Procurement Engineering Audit Checklist
- Flange Facing & Pressure Rating: Confirm standard face-to-face dimensions and flange ratings (ASME Class 150, 300, 600, 900, or 1500).
- Operating Static Pressure: Ensure minimum line pressure meets acoustic signal requirements (>10 bar / 145 psi recommended for optimal ultrasonic performance).
- Communication Protocols: Verify flow computer input requirements (Modbus RS485, HART 7, Foundation Fieldbus, or Ethernet).
- Hazardous Area Certifications: Match site compliance requirements (ATEX Zone 1, IECEx, or Class 1 Div 1).
- Auxiliary Pressure/Temperature Transmitters: Integrate accurate live P&T inputs (e.g., via Rosemount 3051S Wireless Multivariable Transmitter) for real-time gas density calculation.
- Material Test Reports (MTRs): Request EN 10204 3.1 material traceability certificates for NACE MR0175 sour gas compliance.
6. Frequently Asked Questions (Procurement & Technical FAQ)
Q1: Why does the Rosemount 3418 not require a flow conditioner for fiscal measurement?
A: The Rosemount 3418 features a unique 8-path configuration where the second set of chords is a mirror image of the first. This interlocked design allows the meter to mathematically cancel out flow profile distortions like swirl and cross-flow, enabling it to meet OIML Class 0.5 accuracy with just 5 diameters of straight pipe and no flow conditioner.
Q2: How much does a Rosemount 3418 gas ultrasonic flow meter cost?
A: Prices typically range from $15,000.00 to $65,000.00 USD, depending on line size (10" to 42"), flange pressure class, body material, and calibration requirements (e.g., high-pressure natural gas flow calibration).
Q3: Can the transducers be serviced while the pipeline remains pressurized?
A: Yes. The titanium-encapsulated T-200 transducers are specifically designed to be safely extracted under pressure using an extraction tool without blowing down the pipeline or stopping process flow.
Q4: What documentation is provided for custody transfer compliance?
A: Standard shipments include factory calibration certificates traceable to high-pressure natural gas flow calibration facilities (e.g., Eurosam, Pigsar, or CEESI), EN 10204 3.1 material certificates, and hazardous area certificates (ATEX/IECEx).
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