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Clamp On Natural Gas Flow Meter: Custody Transfer Multi-Beam Pipeline Checks
Quick Answer: A multi-beam clamp on ultrasonic flow meter is a practical tool for natural gas pipeline checks. It works best as a verification meter next to the inline custody transfer flow meter. Pipe pressure, gas composition, wall condition and straight run decide the final accuracy.
What a Multi-Beam Clamp On Gas Flow Meter Does
A clamp on gas flow meter mounts ultrasonic transducers on the outside of the pipe wall. The transducers send acoustic signals through the pipe wall and the gas flow. The meter measures transit time difference between upstream and downstream signals. The electronics convert this into flow rate. A multi-beam design uses four or five acoustic paths. That averages the velocity profile better than a single beam. In practice most engineers skip single beam for natural gas lines above DN150.
Silver Instruments supplies clamp on ultrasonic gas flow meters for pipe sizes from DN25 to DN600. The same electronics work on carbon steel, stainless steel and API 5L line pipe. Gas pressure should be high enough to carry a stable ultrasonic signal. We have seen stable readings at 20 bar to 60 bar on dry natural gas. Below 10 bar the signal often gets weak. Higher density gas such as associated gas or wet gas may work at lower pressure. But you should test first.
Why Pipeline Checks Need More Than Single Beam
A single beam meter reads one line across the pipe. That works on clean water and short straight runs. Natural gas pipelines have bends, valves, compressor stations and tee sections. The velocity profile is not flat. A multi-beam clamp on meter samples several paths and averages the result. A four path meter can hold 1.0 percent to 1.5 percent of reading on a well conditioned line. A single path meter may drift 3 percent to 5 percent when the profile changes.
Because custody transfer involves money, the primary meter is usually a fiscal grade ultrasonic, Coriolis or turbine meter. The clamp on meter is the check meter. It tells you if the main meter is reading high, low or drifting over time. We used this setup at a customer site in Vietnam in 2024. The customer had a DN300 natural gas line at 38 bar. The clamp on unit was a four beam portable meter. They compared it against a turbine meter for 48 hours. The average deviation was 0.9 percent.
Typical Natural Gas Pipeline Check Setup
Pick a location with at least 20D upstream and 10D downstream straight run if possible. A multi-beam meter tolerates shorter straight run but do not mount it right after a pressure reducing valve or a compressor discharge. Clean the pipe surface and remove loose paint. Apply coupling compound. Enter the pipe outer diameter, wall thickness, pipe material, gas type, pressure, temperature and flow range. The meter outputs flow in Nm3/h or kg/h. Use the 4-20 mA HART or Modbus output for data logging. Compare that signal with the inline custody transfer meter over at least 24 hours.
One gas processing plant in Malaysia checked a DN400 line at 45 bar in 2023. The team installed the transducers in 40 minutes without shutting down the line. They logged flow data for 72 hours and found a 1.2 percent offset between the check meter and the fiscal meter. This led to a recalibration of the pressure transmitter on the fiscal meter.
Where Clamp On Meters Fit in Custody Transfer Verification
Most national regulations do not accept clamp on meters as the primary fiscal meter for natural gas custo
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So what is the real benefit. You do not have to cut the pipe or stop the gas flow. A field crew can install the transducers on a live line. The check happens without a shutdown and without welding. That saves time on a high pressure gas line. But the measurement is only as good as the input data. Wrong wall thickness or wrong gas composition can create a large error.
Data You Should Send Before You Ask for Price
To get a workable quote from Silver Automation Instruments, send us the pipe outer diameter in mm, pipe wall thickness in mm, pipe material, gas type, pressure in bar, temperature in °C, flow range in Nm3/h or kg/h, and the reason for the pipeline check. Also tell us if the pipe has internal epoxy coating, rust or scale. A photo of the pipe and the nameplate on the existing flow meter helps a lot. Send these details to Tel: +86-135-1213-1526, WhatsApp: 86-135-12131526 or WeChat: +86 13512131526. We respond within one business day.
Common Problems We See on Customer Sites
Here is the thing. Some gas pipes have internal scale or black powder. The ultrasonic signal weakens and the meter cannot pick up a stable reading. Some installations sit too close to a pressure reducing valve. The swirl and jet flow ruin the velocity profile. Some buyers assume a clamp on gas meter works at 2 bar on a small DN50 line. It usually does not. Natural gas needs enough density and a clean acoustic path.
In one job in Oman the customer had a DN100 pipe at 12 bar with wet gas. The first readings were unstable. The field team moved the transducers 15 meters downstream of a bend and cleaned the pipe surface again. After that the flow signal stabilized. Vibration also matters. Do not mount the transducers near a compressor skid or a heavy valve actuator. Mechanical noise disturbs the signal.
FAQ
Can a clamp on ultrasonic meter be the primary custody transfer meter for natural gas? In most countries no. API 21.1 and OIML R 137 require a dedicated fiscal meter. A clamp on meter is for verification and diagnostic checks.
What pipe sizes does Silver Instruments support for gas clamp on meters? Standard sizes are DN25 to DN600. Larger sizes can be quoted on request. The transducer fixtures vary by pipe outside diameter.
Does the meter work on low pressure natural gas lines? It depends on gas density and pipe condition. Below 10 bar on dry natural gas the signal may be weak. We recommend a site test or a pre-survey checklist.
How many acoustic paths do we need for a pipeline check? Four paths or five paths give stable results on DN150 and above. Single beam is not recommended for natural gas because the velocity profile changes too much.
What output signals does the clamp on flow meter have? The standard outputs are 4-20 mA HART, pulse and Modbus RTU. You can use these signals for data loggers, flow computers or site SCADA.
Contact Silver Automation Instruments for a clamp on natural gas flow meter quotation. Tel: +86-135-1213-1526. WhatsApp: 86-135-12131526. WeChat: +86 13512131526. Our team serves pipeline operators, gas distributors and EPC contractors in Southeast Asia, Australia, the Middle East, Africa and Latin America.
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