Jos Abbing
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Industrial low flow applications have to cope with a wide variety of environmental and process conditions, but what does this mean when we talk about ‘industrial’? Knowledge about the specific application and low flow fluidics will help a lot to prevent slipping.

We often refer to ‘uncontrolled macro-environments’ for equipment, when we talk about ‘outdoors’. However, it can also be a room or factory without (local) climate control in which equipment is experiencing comparable temperature and humidity variations as outdoors.

What is important in low flow applications and what kind of challenges do you encounter? Let me share my ideas in this blog.

What is IP-rating?

I experienced that IP-rating is not always interpreted correctly. Having the highest possible IP-rating is often mistaken with having an ‘industrial-device’. But what does the IP-rating actually indicate? The first digit of an IP-rating only refers to dust ingress protection and the second digit refers to the liquid ingress protection.

Therefore, a higher IP-rating does not always mean that the instrument is better and more suitable for your application. Hence, it can even make things much worse in practice. A reason for this is that even the tightest IP-rated constructions may breathe in and out, caused by internal and external temperature variations. This can lead to internal condensation, especially in high humidity environments, if no further precautions are taken.

The importance of dedicated low flow equipment

Not surprisingly, things are often a lot smaller in low flow applications. The other side of this coin is that common process and environmental disturbances have a proportional larger impact on these low flow applications compared to traditional ‘normal’-flow applications.

In general, an industrial flow instrument, like a flow meter, needs to be suitable to a lot of external influences, such as resistance to corrosion and impact or pressure ratings. These requirements often lead to selecting more standard industrial flow meters instead of specialised low flow instruments. This is not always the best solution for the required low flow ranges and can lead to unsatisfactory results.

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What we want to achieve is to have rigid flow measurement and control, suitable for the application during the economic lifetime of the installation. Therefore, it would be best to select the best flow instrument fit for purpose. In case of low flow applications I therefore recommend to use dedicated low flow equipment. These flow meters are designed and tested for these kinds of applications. Our industrial low flow mass flow meters and controllers can be equipped with integrated control valves or dedicated pumps, especially designed for low flow purpose. Stable control characteristics are combined with signal-to-noise ratio plus being proportionally less sensitive for disturbances. Bronkhorst industrial low flow instruments We gladly support you in process and environmental equipment selections including system design aspects, starting with selecting the most suitable measuring and control principles. Our flow meter product portfolio contains laboratory-style and light-industrial flow meters to heavy-duty IEC-Ex/ATEX-rated industrial versions (…having a “high” IP-rating as well).

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Drive your low flow control reliable and safely!

Our product manager for liquid technologies, Ferdinand Luimes, explains how to deal with vibrations using Coriolis mass flow meters

Visit us at the Hannover Messe (April 1-5, Hall 11, booth A50)) and have a sneak preview at our new industrial Coriolis flow meter.

Jos Abbing
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Experiencing harsh industry applications for many years now, I have seen several unpleasant results of corrosion. The global corrosion costs are huge, more than 2000 billion Euros according to NACE. Almost 60% is assigned to industrial use. Especially the chemical, process and oil & gas industry consume an above average share.

These types of industries are coping with demanding environmental and process conditions in production and operation. This includes associated services, such as in heat-transfer systems, transmissions, distribution- and storage of gases and liquids. Prevention or control of corrosion by inhibiting often proves to be an economic solution.

Using a low flow control system can help you dose more accurate amounts of corrosion inhibitors. Accuracy is crucial here; it greatly influences the efficiency and minimizes environmental impact of an inhibitor system.

General corrosion factors

In fact, all metals have a tendency to corrode or dissolve in some degree. Corrosion is a natural process converting metals to a more chemically stable form. The main process (medium) and habitat have a major impact on corrosion risks, such as oxygen, water contents, acidity levels, temperature and other factors.

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Influencing main drivers allow corrosion to be stopped or slowed down sufficiently in which inhibiting can play an important role.

Corrosion resistant by design, e.g. by selection of best compatible material and combinations, additional material thickness and application of protective coatings, may have an initial technical preference to inhibiting. Also metal damage by erosive particles, fatigue or mechanical stress or cavitation may cause corrosion processes which cannot be controlled sufficiently with inhibiting.

However, prevention or control of corrosion by inhibiting often proves to be an economic solution in lots of other situations, improving life time and operational costs with minimum environmental impact. Some relevant examples are to follow.

Examples of metal corrosion

Corrosion can have different drivers and causes:

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Galvanic corrosion requires two different metals that are in electrical contact. When exposed to an electrolyte, a migration of ions from the anode to the cathode causes a release of free electrons. The more noble metal (cathode) is protected and the more active metal (anode) tends to corrode.

Electrochemical corrosion, involving the release of electrons of anodic parts, is related or involved in a lot more corrosion processes, such as concentrated cell (crevice) or pitting corrosion.

Another example is chemical corrosion, which is often induced by strong oxidants, and may not be accompanied by the flow of electric current.

Biological corrosion is caused by the presence and growth of micro organisms. Their direct presence or their corrosion product caused by metabolic activity of the organisms damages the metal which can also lead to pitting or crevice corrosion.

Inhibitor classifications

The task of an inhibitor substance is to slow down or prevent the damage caused by corrosion to acceptable levels. Most corrosion inhibitors used are multi-component mixtures. Below some important examples for (liquid phase) inhibitors.

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Environmental or scavengers inhibitors control corrosion by reducing or removing the corrosive properties in the medium, often involving oxygen reduction.

Interface inhibitors form a protective film on the metal, isolating the metal from the corrosive medium.

Anodic inhibitor will facilitate the formation of passivation layer blocking the anodic process. The critical concentration of the inhibitor is important to secure effectivity and to prevent corrosion acceleration, caused by a too high concentration of inhibitor.

Cathodic inhibitor will decrease the corrosion rate by reduction of oxygen concentrations or increase in the over potential of hydrogen liberation (poison) and precipitate (deposit) on specific cathodic areas (precipitator), forming a protective film.

Mixed or organic inhibitors can moderate both anodic and cathodic principle e.g. by adsorption, chemisorption and film formation. An adsorption processes (physical) is relatively quick but are also more easily removed from a surface, requiring careful control. Chemisorption is a chemical adsorption process, caused by a reaction on an exposed surface, creating an electronic bond of a chemical on the adsorbed surface. The higher the concentration the greater the protection with a limit to a maximum. By exceeding the maximum concentration, corrosion acceleration is often observed.

Enabling smarter dosing control

A corrosion inhibitor system will add (inhibit) small concentrations of (bio) chemicals into the process. The effectiveness of an inhibitor system greatly depends on the correct injection amount. The correct injection amount is also influenced by the environmental- and process conditions.

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The required weight fraction of traditional mix of biocides, other inhibitor substances, agents, surfactants and pH regulators may vary e.g. between 0.001 and 0.1 weight %. Inhibiting system may inject in parts per million (PPM) to achieve low concentrations to be effective. Both continuous- and shot dosing systems are used, based on the situation.

Traditional methods often involve manually tuned piston pumps with check valves. Verification of flow, by changing the stroke length, is often carried out empirically with stop-watch and graduated gauges. This traditional approach virtually makes it impossible to actively compensate to changing process conditions, such as temperature changes (caused by day/night). The result may be the worst-case flow setting, increasing chemical use, environmental impact and also cause over-dosing (!) of chemicals under normal operation conditions.

Accurate flow control

Accurate flow control enables cost effective applications with less environmental impact. High accuracy and high turndown ratio is achieved based on pure mass measurement with mini Cori Flow. This mass flow meter can also directly control valves and pumps by on-board PID control and can be further optimized with PLC and HMI control extending both performance and flexibility.

Coriolis dosing system

Our Coriolis dosing system approach, with digital communication, enables real-time monitoring, control and logging of injection rates. This allows online checking of flow rates and instantaneous re-setting of the required flow rate. Asset management and preventive maintenance is supported with several active diagnostics such as on-board status alarms enabling; steering monitoring, density alarm changes, single or multi point totalisation for costs calculations, empty tank alarm, and pump protection shut down.

Bronkhorst has been supporting field applications and R&D research projects with extensive know how on low flow fluid handling. The ongoing research for even more environmental friendly solutions, such as biodegradable based inhibitors, is gladly supported by us.

James Walton
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Metering and dosing of ultra-low flow rates (g/hr) requires a different approach and understanding of the measuring principle compared to metering and dosing of higher flow rates. At these low levels physics start to play a significant role. In this article I will reveal some of the successes for measuring stable ultra-low flow rates.

Working with people to achieve stable and accurate low and ultra-low flow metering and dosing you learn that little things can make a big difference to the process output.

The first thing to do is understand the measuring principle that is being used, please see the video below for a short explanation on Coriolis measurement theory.

Once the principle has been understood then the challenges that we will face become easier to understand.

Due to the ultra-low flow nature of the application the influence of one area can affect the rest of the system, because of this we have broken our advice down into specific areas of discussion.

Fluid Storage:

  • For pressurised containers avoid using gas that dissolves in liquid, e.g. N2/Air
  • If fluid is water, use Di-Water

Filter Advice:

  • Always use a filter
  • Ensure filter has a large internal volume to minimise pressure drop
  • Outlet needs to be position up to ensure trapped AiR comes out during flush

General Advice:

  • Make sure there are no leaks
  • Make sure the entire system is filled with the same medium
  • Ensure environment stability (temp, humidity, vibration)
  • Use small volume tubes to avoid compliance
  • Use a degasser to remove entrained AiR from the fluid

Image: example of pressurised container with degasser Example pressurised container with degasser

Set-up for success

Firstly, you have to be able to pass the fluid through the tube. This is why you will always be asked to discuss the following points:

  • Pressure
  • Viscosity
  • Density

Knowing these three fluid parameters allows you to calculate (www.fluidat.com) the performance envelope that exists. This is something that is critical in instrumentation to ensure that you size a sensor correctly to achieve optimum performance following installation.

Once the above conditions have been considered and a sensor has been found to meet the requirements of both the fluid and the application you have only the conditions surrounding the sensor that can affect the quality of the readings generated.

All Coriolis instrument reading can be susceptible to external influence from vibration; this is why metering at low and ultra-low flow rates is such a challenging design process. If the environment around the application produces a vibration similar to that of the instrument it can cause false and inconsistent readings. Alongside external vibration issues it is possible to create ‘cross-talk’ where Coriolis instruments mounted next to each other incorrectly can cause interference.

Using mass blocks, considering your environment and allowing for physical functions of instruments in the design process will ensure you can achieve maximum performance.

It is important to discuss these limitations because they exist, however having seen Coriolis instruments on helicopters, at the bottom of the ocean and in submarines it just proves that due care and attention will mitigate low and ultra-low flow liquid metering challenges.

Watch our video explaining the principle of our Coriolis flow meters
Check out our Coriolis flow meter product line