What is it? The gas metering system is the cash register for the natural gas industry. A gas meter tube is a critical section of that measurement system that determines the gas flow rate/volume being transferred through the pipeline. The meter tube consists of straight pipe section that is a precisely machined section of pipe that’s directly upstream of the flow meter. The straight pipe section helps eliminate or minimize turbulence and irregularities in the gas flow to provide a smooth and uniform flow profile across the metering device. A symmetrical flow profile improves measurement accuracy. Often times, there will be a flow conditioner or straightening vane installed upstream of the straight pipe section to help further reduce any turbulent flow conditions.

Meter Run Diagram – highlight on key components

Why is this important?

Irregular gas flow profile = Inaccurate Measurement = $$$ Errors = Someone gets overpaid or underpaid at the custody transfer point

Upstream Production Companies: Measurement discrepancies can affect the Producer, mineral right owners, and the midstream/transmission companies that are purchasing their gas production.

Midstream Transmission Companies: Measurement discrepancies can affect the Upstream Producer, their Midstream Company, and the Downstream purchaser.

Downstream Refinery Companies: Measurement discrepancies can affect the Midstream provider, their Downstream Refinery, and the LDC’s (Local Distributor Companies).

Justification Example:

5% Error on a 10,000 mcf/day meter station = 500 mcf

1 mcf = $5.48

500 mcf = $2,740/day

If that error goes undiscovered for 6 months = $493,200 lost/unaccounted

What should be Inspected?

Flow Conditioner or Straightening Vane: Ensure all the tubes are open and clear of build up and debris. Depending on the location of the meter run, these tubes can become clogged with sludge and corrosion. If it’s a new location, there could be welding rods, wood, mud, gloves, whatever the pipeline workers left in the upstream pipeline. Certain types of Straightening Vanes are held in place by a set screw that can occasionally break loose or back off causing the Straightening Vane to move too far down the straight section of the meter tube.

Straightening Vane

Flow Conditioner

Debris Found in Meter Tube

Straight Pipe Section: Ensure there is no build up, sludge, corrosion along the polished/machined surface of the pipe. Build up within the straight section can reduce the inside diameter of the meter tube resulting in turbulent flow conditions and over accounted gas volume being measured. (Depending on when the error is discovered and the contractual agreement, this can result in the company back paying/correcting for any over accounted volume up to 2 prior years. = Accounting Nightmare!)

Meter Tube Straight Section – shows corrosion and build up on the polished straight section of the meter tube

Pressure Taps & Differential Pressure Ports: Ensure there’s no build up, sludge, corrosion within the pressure taps and along the wall of the Differential Pressure Ports and Tubing to the meter. Build up in the Differential Pressure Port and Tubing can have a major impact on the meter accuracy.

Orifice Fitting: Ensure the sealing surface where the orifice plate seal ring seals against the meter tube is smooth and flat. If it’s a dual chamber fitting, you can insect the gear teeth that roll the orifice plate carrier in/out for damage, without having to remove the gear shaft.

Carrier Gear Shaft – Gear teeth of a Carrier Gear shaft on a Senior Orifice Fitting

Our Solutions: Our iPLEX G Lite or IPLEX GT 6mm diameter and 3.5 meter length are ideal for this application. Since accessibility is not an issue, the 6mm diameter is best, and 3.5 meter length will be sufficient to inspect the full length of the meter tube.

The portability of the G Lite provide the technician flexibility and ease of maneuvering around the meter run, but the screen size and visibility of the GT under bright, sunny conditions allow for better viewing quality and easier on-site decision making. Our MIL-STD 810G Explosive Atmosphere Compliance is a critical certification to this application. Measurement is not typically required. For a detailed meter tube inspection, the tube is taken out of service and verified with precision instruments.