Flow Measurement
Insertion Flow Meter vs Full Bore Flow Meter: Selection Guide
Insertion flow meters place a sensor element into the pipe through a small bore fitting. Full-bore flow meters replace a section of pipe and measure across the entire cross-section.
Choosing between them depends on pipe size, fluid type, accuracy needs, installation constraints and long-term maintenance requirements.
Insertion Meter
Full-Bore Meter
Hot Tap
Pipe Size
Selection Guide
Hello everyone, today we are going to learn about insertion flow meter vs full bore flow meter and how to select the right type for your application.
We will cover how each design works, where each one is the better choice, and what factors drive the decision including pipe size, accuracy, cost, and fluid conditions.
We will also look at a comparison table across the key selection criteria and a set of practical guide rows to help you decide quickly in the field.
We will cover how each design works, where each one is the better choice, and what factors drive the decision including pipe size, accuracy, cost, and fluid conditions.
We will also look at a comparison table across the key selection criteria and a set of practical guide rows to help you decide quickly in the field.
Getting this selection right at the project stage saves money and avoids costly retrofits. The wrong choice can mean poor accuracy, high maintenance, or a full pipe shutdown to replace the meter.
Insertion Flow Meter vs Full Bore Flow Meter: What Each One Is
Insertion Flow Meter
A sensor element is inserted through a fitting into the pipe, typically reaching the pipe centerline or a defined insertion depth.
The meter measures velocity at one point or a small number of points, then converts this to flow using a known pipe cross-sectional area.
Available as insertion magnetic, insertion vortex, insertion turbine, averaging pitot tube, and thermal mass types.
Full-Bore Flow Meter
The meter body replaces a section of the pipe spool and provides measurement across the full internal diameter.
All of the flowing fluid passes through the meter body. Measurement uses the full velocity profile, not a sample at one depth.
Available as magnetic, coriolis, vortex, turbine, ultrasonic, and differential pressure element types.
Key Factors That Drive the Selection
Pipe size
Full-bore meters are practical up to about 600 mm diameter. Above that, insertion meters are almost always the cost-effective choice. A full-bore magnetic meter for a 1000 mm water main costs far more than an insertion magnetic probe with a hot-tap fitting.
Accuracy
Full-bore meters typically achieve 0.2 to 0.5% of reading. Insertion meters typically achieve 1 to 3% of reading when measuring at a single point. An averaging insertion type improves accuracy but still trails a well-calibrated full-bore meter.
Fluid cleanliness
Insertion meters are more vulnerable to fouling and damage from particles, fibres and slurry because the sensor tip is exposed inside the flow. Full-bore meters handle dirty fluids better, particularly lined magnetic meters with no moving parts.
Installation
Insertion meters can be hot-tapped into a live pressurised pipe without shutting down the process. Full-bore meters require a full pipe break, a shutdown, flanges cut in, and a pressure test before return to service.
Maintenance
Insertion meters can be retracted and replaced without depressurising the system if a retraction mechanism is fitted. Full-bore meters require isolation valves and a shutdown for any internal maintenance.
Pressure loss
Insertion meters produce negligible permanent pressure loss. Full-bore differential pressure elements (orifice plates, venturi tubes) produce significant permanent pressure loss. Full-bore magnetic and ultrasonic meters are near-zero loss like insertion types.
Custody transfer
Custody transfer metering almost always uses full-bore meters with traceable calibration certificates. Insertion meters are generally not accepted for custody transfer because single-point velocity sampling cannot meet the required uncertainty levels.
Full Comparison Table: Insertion vs Full-Bore
| Parameter | Insertion Flow Meter | Full-Bore Flow Meter |
|---|---|---|
| Pipe size suitability | Best for 200 mm and above; cost-effective in large pipes | Best for 15 mm to 600 mm; expensive above 600 mm |
| Typical accuracy | 1 to 3% of reading (single point); 0.5 to 1% for averaging types | 0.2 to 0.5% of reading for magnetic, ultrasonic and coriolis |
| Shutdown required to install? | No, hot-tap insertion possible | Yes, full pipe break and shutdown required |
| Installation cost | Low: one fitting, no flanges, no spool piece | High: two flanges, spool piece, gaskets, bolting |
| Meter purchase cost | Low to medium | Medium to very high (scales with pipe size) |
| Permanent pressure loss | Negligible | Zero (magnetic/ultrasonic) to high (orifice plate) |
| Velocity profile sensitivity | High: single-point types need long straight run | Lower: full-bore types are less affected by profile distortion |
| Dirty or abrasive fluids | Poor: sensor tip is exposed to the fluid | Good: lined magnetic meters handle slurries well |
| Retractable under pressure? | Yes, if retraction mechanism is fitted | No: requires isolation valves and shutdown |
| Custody transfer use | Not accepted in most standards | Yes, widely accepted with calibration certificate |
| Gas measurement | Thermal mass insertion and averaging pitot types work well | Coriolis and vortex full-bore types preferred for gas |
| Typical applications | Large water mains, HVAC, cooling water, plant utilities, air ducts | Process plant, fiscal metering, custody transfer, chemical dosing |
When to Choose Each Type in Practice
Choose an insertion flow meter when the pipe is 300 mm or larger and a process shutdown is not acceptable. It suits utility monitoring and energy metering with clean, non-abrasive fluids.
Choose a full-bore flow meter when accuracy better than 1% is required or the fluid is dirty.
It is also the right choice for custody transfer, or when the pipe is small enough for a full-bore spool piece.
Insertion depth matters for accuracy.
A single-point insertion meter placed at the pipe centerline reads the peak velocity, not the average velocity. The meter manufacturer provides a correction factor or profile factor to convert the centerline velocity to average velocity. This factor changes with Reynolds number and with the velocity profile shape. If the profile is distorted by an upstream fitting, the correction factor no longer applies and error increases. Always provide the specified straight pipe run upstream and downstream of any insertion meter to keep the profile symmetric.
A single-point insertion meter placed at the pipe centerline reads the peak velocity, not the average velocity. The meter manufacturer provides a correction factor or profile factor to convert the centerline velocity to average velocity. This factor changes with Reynolds number and with the velocity profile shape. If the profile is distorted by an upstream fitting, the correction factor no longer applies and error increases. Always provide the specified straight pipe run upstream and downstream of any insertion meter to keep the profile symmetric.
Technology Variants Available in Each Category
| Technology | Insertion Version Available? | Full-Bore Version Available? | Best Application |
|---|---|---|---|
| Electromagnetic | Yes, single probe or multipoint FPI | Yes, standard lined mag meter | Conductive liquids: water, slurry, chemicals |
| Ultrasonic | Yes, insertion transducers | Yes, clamp-on or spool piece | Clean liquids and gases; large pipe retrofit |
| Vortex | Yes, insertion vortex types available | Yes, wafer or flanged body | Steam, gas, clean liquids above minimum velocity |
| Turbine | Yes, insertion turbine probes | Yes, axial turbine body | Clean low-viscosity liquids and gases |
| Thermal mass | Yes, most thermal mass meters are insertion | Yes, inline types for small pipes | Gas flow, compressed air, nitrogen, biogas |
| Averaging pitot tube | Yes, this is an insertion type by design | No | Gas and liquid in large pipes and ducts |
| Coriolis | No | Yes, U-tube or straight tube body | Mass flow, density; highest accuracy requirement |
| Orifice plate | No | Yes, between flanges | Steam, gas, liquid; most established DP type |
Watch: Insertion Mag Flow Meter Comparison Explained
Insertion Flow Meter vs Full-Bore Flow Meter Questions
What is the main difference between an insertion and a full-bore flow meter?
An insertion meter places a sensor into the pipe through a small fitting and measures velocity at one or a few points. A full-bore meter replaces a pipe spool and measures the full cross-section. Full-bore types give better accuracy; insertion types cost less in large pipes.
Can an insertion flow meter be installed without shutting down the pipe?
Yes. Insertion meters use a hot-tap fitting on a pressurised pipe without stopping the flow. A valve on the fitting allows the probe to be inserted and locked in position. Full-bore meters require a complete shutdown and isolation.
Which type is more accurate, insertion or full-bore?
Full-bore meters are more accurate. A calibrated full-bore magnetic or coriolis meter achieves 0.2 to 0.5% of reading. A single-point insertion meter achieves 1 to 3%. An averaging insertion type can reach 0.5 to 1% with good installation.
For which pipe size is an insertion meter better than a full-bore meter?
Insertion meters become more cost-effective above 200 to 300 mm pipe diameter. Above 600 mm, a full-bore meter spool piece is very expensive and an insertion meter is almost always the practical choice for non-fiscal applications.
Can insertion flow meters be used for custody transfer metering?
No. Custody transfer metering requires full-bore meters with factory calibration certificates traceable to a national standard. Insertion meters measuring at one or a few points cannot achieve the uncertainty levels required by AGA, API or ISO custody transfer standards.
Related Articles on This Site
- Types of Flow Meters and Their Applications
- Magnetic Flow Meter Sizing and Installation
- Vortex Flow Meter Working Principle
- Orifice Plate Flow Measurement Explained
- Ultrasonic Flow Meter Troubleshooting Guide
External References
What We Learn Today
- An insertion flow meter places a sensor into the pipe through a small fitting and measures velocity at one or a few radial points. A full-bore flow meter replaces a pipe spool and measures across the full cross-section. Insertion meters cost far less in large pipes and can be hot-tapped into a live system without a shutdown.
- Full-bore meters give better accuracy (0.2 to 0.5% of reading) than single-point insertion types (1 to 3%). Full-bore meters are required for custody transfer metering and handle dirty or abrasive fluids better. Insertion meters are the practical choice above 300 to 600 mm pipe diameter for utility and non-fiscal applications.
- Both technologies are available in electromagnetic, ultrasonic, vortex and turbine versions. Thermal mass and averaging pitot tube meters are predominantly insertion types. Coriolis and orifice plate meters are only available as full-bore designs. The selection decision always starts with pipe size, accuracy requirement, and whether a shutdown is acceptable.
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