Shape Matters: The Benefits Of Cone-Type Flow Meters
Selecting the proper flow meter will take an operator through a fairly typical vetting process, including consideration of capital expenditure (CAPEX), O&M requirements, effectiveness, and durability. Manufacturers of all meter types (e.g., Venturi meters, magnetic flow meters (magmeters), cone meters, etc.) will surely claim to excel in these categories, but can they back up the claim?
During a recent discussion with Nick Voss of McCrometer Inc., I challenged him to get specific on the performance aspects of the V-Cone differential pressure (DP) flow meter. For those unfamiliar with the functionality of a cone meter, his answers to the key decision-making parameters — cost, maintenance, and reliability — may provide food for thought as you analyze your options.
CAPEX includes not only the cost of the product itself, but the cost of installation. Voss attests that the prime advantage of the V-Cone is the minimal space and piping required. The cone shape conditions swirling, and therefore eliminates the need for long straight runs of pipe to settle the flow. According to Voss, a Venturi DP meter will often require 10 to 15 pipe diameters of straight run (distance in inches divided by nominal pipe size), while magmeters do slightly better at 5 to 10 diameters. In most cases, the V-Cone requires no straight run at all, saving space and construction costs. The V-Cone can thus be installed in relatively close proximity to valves, pumps, pipe elbows, etc. for space-constrained environments.
Subsea skids for oil and gas (O&G) exploration, for example, require a small footprint, since space parallels expenditure. “For every pound that you put on the ocean floor, there is extra cost associated with it,” Voss noted.
He also cited saving for onshore applications, where the lack of pipe run required for the V-Cone reduces the cost for steam-injection applications. Steam lines need to be insulated, which is expensive not just for installation, but also because long pipe runs require a hotter boil to maintain temperatures and steam.
Whether deep under sea or at the treatment plant, recalibration and repair of a flow meter is an unwelcome necessity … or is it? The V-Cone almost never needs recalibration or repair, due to no moving parts and a very small and robust electronics package, according to Voss.
“The only thing you might have to do is test the transmitter once a year or every other year — standard maintenance on a piece of electronics and a very simple operation that can be done without pulling the meter or shutting down the line,” he said. “You can leave the line up and running for longer because you don't have to pull the primary element or the flow meter for repair or recalibration.”
About a year ago, I reported on some financial analysis stating that high-tech flow meter types (ultrasonic, coriolis, and magmeters) were set to take over “traditional” types such as differential pressure meters. User feedback seemed to suggest “not so fast,” and it is obvious that DP meters are the preferred fit for certain applications. Voss contends that ultrasonic and magmeters, in addition to needing long straight runs, are susceptible to noise disturbances. Pump motors, variable speed drives, electronics cabinets, or any electrical noise can interfere with electronic sensing devices, causing inaccurate readings. Some magmeter suppliers, McCrometer included, can overcome sound interference through various installation techniques such as grounding of the meter, specialized cabling, and other means. However, DP meters — as well as turbine meters, positive displacement meters, and orifice plates — are naturally immune to electrical noise.
To illustrate the importance of accuracy, Voss detailed (one of) the implications for municipal drinking water treatment operations:
“The more accurate your measurement, the more accurate your processes — for example, chemical dosing. The flow meter often controls how much chlorine is applied within the various stages of treatment; if you have a meter that's inaccurate, you run the potential of underdosing the water. To compensate, a lot of water treatment plants will overdose, or put extra chemicals in, to ensure the water is safe to drink. By accurately measuring how much water you’re producing, you can more accurately dose the water, which saves money on an ongoing basis.”
As previously mentioned, O&G companies depend on flow meters for demanding environments such as subsea operations and offshore platforms. Cone meters feature a contoured shape that resists wear — the V-Cone having a life expectancy of 25 years. Orifice plates, by contrast, have a tendency to wear much more quickly (in as little as a year), according to Voss, in addition to needing up to 40 diameters of pipe run. Venturi meters have a similar lifespan to V-Cone meters, but the differentiating factors for the latter are zero pipe run and no maintenance or recalibration requirements. Magmeters, meanwhile, are entirely unsuited for many O&G applications in that they fail to measure nonconductive fluids like hydrocarbons gases and liquids
Applications And Limitations
Where doesn’t the V-Cone fit?
“In municipal wastewater, because the water is dirty, you wouldn't really want to use any differential pressure-type meter,” explained Voss. “But within clean water and drinking water, it can be put just about anywhere — in the treatment plant, in the distribution system, in vaults serving water throughout the distribution network for leak detection — there really isn't an application that doesn't suit the meter.”
In O&G, the V-Cone is not meant to measure highly viscous and dirty oil flows such as “heavy crude,” but does specialize in the water, natural gas, steam, lighter oil, and hydrocarbon condensate measurements that are essential to the exploration and production process.
Alternate flow meter technologies and types can surely fill the gaps where the V-Cone is not ideally suited — pros and cons abound across the spectrum of measurement devices. But when it comes to the applications prescribed above, cone meters seem to shape up quite nicely.