Liquid assets

In the high-stakes oil and gas business, the accuracy of flow meters used in the transfer of high value assets must be right on the money.

While most of the instruments tasked with measuring ‘custody transfer’ sit between customers and their suppliers, they might also be tasked with measuring the flow between the pipelines connecting continents.

“In these applications, every number behind a comma makes a difference,” says Tim Vogel, product marketing manager of gas metering at Honeywell Process Solutions.

Our equipment is used where ownership of gas switches from one person to the next

HPS marketing manager Tim Vogel

Honeywell’s focus is in gas transmission and distribution, or in applications where gas is used to power a process such as in gas fired power plants.

“Normally our equipment is used where ownership of gas switches from one person to the next, so we call our meters the ‘cash registers’ of the industry,” says Vogel.

The company supplies a range of gas metering products, he says, including turbine and vortex meters, but its flagship is an ultrasonic flow meter called the USM GT400.

Designed for demanding gas flow measurement applications, the flow meter measures volume as well as quality.

But choosing an instrument isn’t purely about accuracy or ease of use.

“We are seeing a lot more focus on safety,” says Vogel.

“Customers want safe operations that are maintenance-free.”

Emerging industries and environmental regulations are also steering the market into new terrain.

When it comes to environmental considerations, the main discharge streams in oil and gas production are produced water and flaring or venting gas, says Alick MacGillivray, a senior consultant at flow measurement specialists NEL.

The most widely used flow meter for greenhouse gas emissions flared from oil and gas production facilities, and other process plants, is the time-of-flight ultrasonic meter (USM), says MacGillivray.

“These streams should be measured directly by a flow meter in the discharge line,” he says.

Water discharges must also be measured, generally with electromagnetic meters or orifice plates, which are inspected by the Department of Energy and Climate Change (DECC).

“This means flow meters must be properly and regularly calibrated, verified and maintained,” says MacGillivray.

Vogel says that across Europe, there is also an increased push to generate renewable energy in biogas plants.

And on a more global level, the gas appliance is evolving as a result of the shale gas boom, with LNG now being shipped around the world.

“Meters must definitely be developed to cope with those new demands,” says Vogel.

“We’ve been trying to adapt technologies already there and reuse them.”

Another area of interest is the potential of using software to remotely monitor a meter by adding a little bit of artificial intelligence to it.

“In this scenario the meter understands what is going on and gives an operator the means to make the right decision,” says Vogel.

“We’ve already started seeing this in the oil sector where data from meters is fed into big Distributed Control Systems (DCS).”

Custody transfer is one of the most important applications of flow measurement for oil and gas producers, distributors, and end users, says global research group Frost & Sullivan.

New flow meter technologies such as ultrasonic offer increased accuracy and reliability, and these improvements also enhance the performance of traditional meters, it says.

Ultrasonic flow meters are widely used for the custody transfer of liquids and gases, and their major advantage is that they can handle large line sizes of pipelines that range from 20 to 42 inches, says the researcher.

Other advantages of ultrasonic meters include their lack of moving parts, their high levels of accuracy and reliability, and their lack of pressure drop, although they do require periodic recalibration.

A recent convert to ultrasonic flow metering is Eurac Poole, a grey iron foundry that makes cast iron.

Molten iron is prepared in coreless induction furnaces and as cooling water is circulated through an electric induction coil, it is crucial that flow is monitored constantly because, if water is lost, the electrical coil could melt, seriously compromising safety.

Furthermore, a replacement coil costs £35,000, in addition to any collateral damage and loss of production.

Eurac Poole maintenance superintendent Paul Sillence says he had used electro mechanical flow monitoring devices previously, but found them to be unreliable.

He wanted a non-invasive alternative that would constantly measure the flow in a closed loop cooling system through an evaporative cooling tower, and would be easy to fix without any need to break into the system.

He selected a U3000 Ultrasonic Liquid Flow Meter from Micronics to be fixed on pipework serving the cooling system.

Because no mechanical parts had to be inserted through the pipe wall or to protrude into the flow system, Sillence says the installation took just a few minutes.

Another flow meter technology associated with extremely high-accuracy levels is coriolis, which is mainly used for the custody transfer of liquids.

“Coriolis works on mass flow rather than volumetric which makes it more suitable for fluids that change with different temperatures,” says Ashley Buck, coriolis product manager at Bronkhorst.

Bronkhorst supplies the coriolis flow metering technology commonly used in dosing applications across a range of industries from pharmaceutical, to oil & gas and heavy industrial chemicals.

Coriolis flow meters were originally designed to replace a weighing scale, says Buck.

“Previously, if you wanted to dose a fluid into a process you put a beaker on the weighing scale and measured it,” he says.

“The coriolis flow meter allows you to dose directly into process. Because coriolis works on a mass basis, it is more accurate as you can guarantee the flow you are measuring.”

To illustrate why this is important, Buck says he visited a site that insisted on using volume measurements and fixed weights to dose their process, but routinely ended up with 200 to 300 grams less than they thought they had.

“This was because it was ten degrees inside the room and two degrees outside it,” says Buck.

The results of over or under dosing can have serious consequences.

“If you are overdosing you can create a hazard or damage the end product,” says Buck.

“Or you could be wasting an expensive fluid which adds up to a substantial extra cost over a period of time.”

One development that is making the technology even more attractive to users that require high accuracy and traceability is the ability to track fluid usage and use that data to generate better reports for use internally or for external regulators, says Buck.

Another supplier of coriolis flow technology is Emerson Process Management, with a range of products aimed at especially hazardous or highly corrosive environments.

Although it sells a range of flow meters, including magnetic, vortex and ultrasonic, coriolis is the most accurate for custody transfer applications says Thomas Otten, chemical business development manager of flow products at Emerson Process Management.

“Economic pressures mean many companies are now being forced to be even more reliable and productive with the same inventory,” he says.

In utilities where accuracy is less critical, then a magnetic, vortex or ultrasonic flow meter can be considered adequate, he says.

Emerson also supplies instruments with internal verification features.

“That is what we call smart meter verification, where you can verify function and reliability without taking the meter out for calibration,” says Otten.

This allows them to verify the meter without any additional workload such as having to put their process into a specific condition to discover whether a pipe is corroded.

“If the fingerprint changes then you know there is something to look at the next time you maintain the instrument,” adds Otten.

Another development to watch out for is the inclusion of wirelesscontrolled technology in flow metering devices.

“While most devices are currently only used for monitoring, the next step is controlling the process,” he says.

“By advancing this technology we will be able to put these systems into the control loop.”