Hydrogen effect on piezo transducers (bio fouling)

Hydrogen effect on piezo transducers (bio fouling)

BIOFOULING

Biofouling or biological fouling is the accumulation of microorganisms, plants, algae or animals on wetted surfaces, devices such as water inlets, pipework, grates, ponds and of course on measuring instruments, causing degradation to the primary purpose of those items.

ANTIFOULING

Antifouling is the process of removing or preventing these accumulations from forming. There are different solutions to reduce / prevent fouling processes at the ship hulls and in sea or brackish water tanks.

Special toxic coatings that kill the biofouling organisms; with the new EU Biocide directive many coatings were forbidden due to environment safety reasons.

  • Non-toxic anti-sticking coatings that prevent attachment of microorganisms on the surfaces. These coatings are usually based on organic polymers. They rely on low friction and low surface energies.
  • Ultrasonic antifouling. Ultrasonic transducers may be mounted in or around the hull on small to medium-sized boats. The systems are based on technology proven to control algae blooms.
  • Pulsed laser irradiation. Plasma pulse technology is effective against zebra mussels and works by stunning or killing the organisms with microsecond duration, energizing of the water with high voltage pulses.
  • Antifouling via electrolysis
  • Organisms cannot survive in a copper ions environment.
  • Copper ions occur by electrolysis with a copper anode.
  • In most of the cases, the tank housing or the ship hull serves as cathode.
  • A copper anode installed in the configuration generates an electrolysis between the anode and the cathode.

Electrolysis can appear due to ballast water treatment systems (electrolysis and UV-sytems), corrosion processes or differences of electric potential between different materials.

EFFECT OF ELECTROLYSIS ON THE PIEZO RESISTIVE TRANSDUCER

  • A result of the electrolysis are positive hydrogen ions
  • Because of their polarization, the hydrogen ions move towards the cathode (tank housing or ship hull) where the transducer is installed.
  • In case of direct contact between tank and transducer, the hydrogen ions will permeate through the thinnest component of the anode, which is the diaphragm of the transducer.
  • After permeation of hydrogen ions through the diaphragm, the hydrogen ions grab an electron and transform into molecular hydrogen (H2). The hydrogen accumulates in the fill fluid of the transducer.
  • If this effect lasts for a longer period, the concentration of hydrogen in the fill fluid will increase and the diaphragm will be bloated. As a result, the sensor drifts and issues an incorrect value.

FINDINGS

Stainless steel pressure transmitters used during 2-3 years in ballast tanks of ships were investigated by the Swiss Federal Laboratories for Materials Science and Technology in Zurich.

Findings

The formation of deposits on stainless steel membranes cannot be prevented in practice. As long as corrosion processes can take place on the membrane under anaerobic conditions, the formation of hydrogen and its penetration into the sensor must always be expected.

For this reason, under such conditions, the membrane should be made of a more corrosion-resistant material such as titanium.

Gap corrosion occurs on metal parts in presence of a corrosive medium in narrow, unsealed gaps such as overlaps and in welds that are not through-welded. The driving force is concentration differences between the medium in the gap and the area outside the gap, which are caused by the inhibited diffusion of the reactants in the gap. The potential difference associated with the concentration difference leads to electrochemical corrosion in the gap (hydrogen type) or its immediate surroundings (oxygen type).

For this reason, the membran should be welded to the housing.

RECOMMENDATION

According to this findings, STS Sensor Technik Sirnach AG has been successfully using piezo-resistive elastomer-free sensors with housing and membrane in titanium for applications in marine, brackish water and sea water applications for over 10 years.

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Dependable fill-level control in coal mining

Dependable fill-level control in coal mining

Mine workings and opencast pits are well known for their harsh working conditions. This applies equally to the technology deployed. For this reason, durable and reliable measuring instruments are required to monitor groundwater.

Ten percent of worldwide coal deposits are to be found in Australia. As the leading coal exporter, coal mining is one of the most important economic factors on that continent. Mining of the raw material, however, is not without its pitfalls. The operator of an Australian opencast approached STS as they were seeking a pressure transmitter for fill-level monitoring at depths of up to 400 meters.

Mining operations have a heavy influence upon groundwater. The aquifers surrounding the coal mine become drained, which leads to a sinking of the depression cone. This sinking alters the natural hydrological conditions underground by creating paths of lowered resistance. What this then leads to is water penetrating the open pit and underground workings. As a result, the constantly inflowing water needs to be continuously pumped out of the pit to ensure a smooth and safe extraction of the raw material.

To control the groundwater level and the pumps used for drainage, the operators of the opencast needed a pressure transmitter to monitor the fill-level according to their requirements. Stipulated was a pressure range from 0 to 40 bar (400 mH2O) ambient pressure, as well as a cable length of 400 meters. The solution offered by STS at that time, the ATM.ECO/N/EX, read only to 25 bar and had a cable length of 250 meters.

But since STS is specialized in customer-specific pressure measurement solutions, this challenge was to prove no major obstacle. In short time, the failsafe ATM.1ST/N/Ex pressure transmitter for fill-level was developed, which precisely meets the pressure requirements and is equipped with a 400-meter-long Teflon® cable. It is also convincing in its accuracy of just 0.1%. STS decided upon development of the new pressure transmitter for a Teflon® cable, a sealed cable gland and an open aeration tube (PUR is too soft for this). In addition, there is also a screw-on ballast weight to ensure a straight and stable measuring position. The stainless steel strain relief, which can also be screwed on, helps to relieve strain on the electrical cable. As the device designation indicates, it also carries the EX certification for use in explosive areas.

ATM.1ST/N/Ex with strain relief (left) and ballast weight (right), each screw-on.

Being an expert in customer-specific pressure transmitters, STS was able to supply the ATM.1ST/N/Ex in less than three weeks.

The features of the ATM.1ST/N/Ex in brief:

  • Pressure range: 1…250 mH2O
  • Accuracy: ≤ ± 0.1 / 0.05 % FS
  • Total error: ≤ ± 0.30 %FS (-5 … 50°C)
  • Operating temperature: -5…80 °C
  • Media temperature: -5…80 °C
  • Output signal: 4…20 mA
  • Materials: Stainless steel, titanium
  • Electronic compensation
  • Common process connections available
Applications of pressure measurement technology in the marine industry

Applications of pressure measurement technology in the marine industry

Sensor technology plays an essential role in the maritime sector and most particularly in shipbuilding. The dependable and accurate measurement of pressure, temperature and other variables within various tanks is an important measure in preventing the escape of aggressive fluids, controlling water circulation systems in ship operations and also in guaranteeing a smooth transportation of cargo across the high seas. 

The sensor technology employed here has to meet numerous stringent requirements. These include, above all, that the materials utilized are robust enough for use over the longer term. The electronics must also be capable of withstanding the harsh conditions of the open seas and therefore remain highly durable.

Monitoring of dry and liquid cargoes

The main component of freight consists of wares to be shipped, with both dry and liquid cargoes being transported by sea. Dry cargo is the term we use when bulk goods such as grain and animal feed, as well as piece goods usually held in containers, are being transported. Liquid cargoes, however, require particularly careful and reliable monitoring, since highly sensitive substances, including gasoline, oil and gas oil, are usually being transported here. The products employed must be particularly robust and reliable in order to prevent the escape of aggressive liquid substances and thus prevent accidents of the gravest ecological consequences. This means that sensory systems must also meet the very highest of demands.

Freshwater and wastewater tanks

On cargo ships, fresh or drinking water is either carried in special potable water tanks or obtained from seawater through a purification treatment. The collection, treatment and disposal of ship wastewater in internal storage systems must also be monitored using an appropriate technology. Since this wastewater is often contaminated with harmful substances, such as oils or cleaning agents, its processing also remains subject to certain additional requirements. Both freshwater and wastewater tank systems are checked and monitored using built-in sensors. In this way, the systems can be monitored most efficiently, which in turn guarantees an optimum water supply across the high seas.

Ballast tanks

Ballast tanks are an important part of shipping. Without loading these tanks, large cargo ships can sometimes be too light, meaning that their propellers will not sit deep enough in the water. To ensure a sufficient draught, the ballast tanks are filled up with seawater and can even be used to even out the weight distribution across a loaded ship. Since these tanks are being filled with saltwater, both the materials of the tanks and those of the sensors used must be robust and corrosion-resistant. Special attention is also paid to high reliability and durability, since the sensors are virtually inaccessible underway during on-board operation and must therefore function perfectly without any manual maintenance or inspection.

Image 1: Level measurement installation options

Special sensory requirements

Over the last few years, the shipbuilding industry has seen a steady stream of decisive innovations to which the production of sensors employed must respond accordingly. Whereas 15 years ago, for example, the durability of stainless steel was still a major concern, today we recognize that it corrodes when it comes into contact with saltwater at temperatures above 21 degrees Celsius. Nowadays, titanium is employed instead. STS recognized this problem early on and was one of the first companies to use titanium as a permanent component of its sensing technology. This extremely stable and robust material is now used as standard for a wide range of pressure transmitters and immersion probes, since it can withstand even the most adverse of conditions.

The technological requirements are constantly changing as the industry itself grows and evolves. What was considered standard a short time ago may already be inadequate by today. STS is therefore constantly striving to further develop the sensing technology it offers, thus guaranteeing reliability and accuracy, even in the face of increasing industrial demands. This flexibility and quality does pay off, however, with return rates negligibly low and problems more likely to arise from human error than through faulty technology.

Collaboration with AE Sensors

For over 27 years now, STS has been working together with the Dutch family-run company AE Sensors. Together, we supply major customers in the shipbuilding industry with their sensing technology. With competent consulting and the use of flexible solutions, our customers have been able to record enormous growth in just a short period of time. By now, state-of-the-art vessels are being built at shipyards all over the world, in which submersible probes, pressure transmitters and other tailor-made solutions from STS are being used. Above all, our ATM/N and ATM.1ST/N sensors made of titanium and fitted with Teflon cables are being deployed as standard.

Thanks to their modular mounting system, installation of our sensors can be variably adapted to the prevailing requirements. Various forms of measurement, such as positive or absolute pressure, may also be implemented. The high flexibility of STS and our partner AE Sensors, combined with the flawless quality of our sensing technology, has proven itself over many years of cooperation with our satisfied customers.

Research project DeichSCHUTZ: Reliable measurements for safer waterfronts

Research project DeichSCHUTZ: Reliable measurements for safer waterfronts

In extreme flood situations, the hopes of those people affected lie solely with the dykes – will they hold or not? A dyke failure like the 2013 flood in Fischbeck (Saxony-Anhalt) caused immense damage to inland areas, which continue to have an impact to this day. The active research project DeichSCHUTZ (dyke protection) at the Bremen University of Applied Sciences is involved in an innovative dyke protection system that could prevent failures of this kind.

In Germany alone, river dykes safeguard many thousands of kilometers of waterfront lands. From today’s technological perspective, dykes consisting of three zones are being constructed. The individual zones, viewed from the water-side to the land-side, are built with steadily increasing porosity, thus affording good drainage of the dyke body during a flood event. In Germany, however, many older dykes of homogenous construction do still exist, such as the dyke breached during a flood of the River Elbe in June 2013 in Fischbeck. In contrast to the 3-zone dykes, older ones are particularly vulnerable to prolonged flood conditions. Water seeps into the dyke itself and its saturation line rises further within the dyke body over extended periods of high water. The further this saturation line rises, the more the ground material is subjected to buoyancy. The dyke thus loses its own essential self-mass, required to counteract against the pressure of high water.

Stabilization of a breach-prone dyke requires enormous resources in material and personnel, as well as time, which in acute flood situations is a scarce commodity.  Backup procedures are thus required, which, in terms of personnel, materials and time commitment, are more effective than layering sandbags on the landward side of the dyke.

Innovative mobile dyke protection system

Christopher Massolle of the Institute for Hydraulic and Coastal Engineering at the Bremen University of Applied Sciences is developing a solution that can considerably reduce the input of time and personnel. With the DeichSCHUTZ research project, sponsored by the Federal Ministry for Education and Research, an innovative, mobile dyke protection system is being tested for stabilizing dykes during flooding events. Measurement technology supplied by STS is also playing a role here.

To assess the mobile dyke protection system, a test-dyke has been built on the premises of the Agency for Technical Relief in Hoya. To this end, a U-shaped retention basin holding some 550 cubic meters of water has been constructed, at whose end sits a dyke.

As can be seen in the video, numerous pipes have been deployed at the left side of the dyke. Within these pipes rest ATM/N Level Sensors produced by STS. In the test arrangement, the retention basin is filled with groundwater. Under conditions approaching reality, the water should rise to a level of 3 meters over a period of 30 hours. The submersible level sensor ATM/N  now measure development of the saturation line over this time. With a pressure range from 1 to 250 mH2O and an accuracy of ≤ ± 0.30 %FS (-5 to 50 °C), this is recorded down to the very last centimeter. When the saturation line no longer continues to rise, the mobile dyke protection system is introduced to the water-side slope and should prevent the further penetration of seepage water. The dyke body now continues to drain and the extent of the resulting shift in the saturation line is to be measured by the level sensors employed. It is from these measured results that the functionality of the protection system can lastly be assessed.

Reliable groundwater and surface water monitoring in Romania

Reliable groundwater and surface water monitoring in Romania

A seamless control system with alarm function is required to perform precise water level measurements and to make reliable forecasts on potable water supply, as well as to anticipate floods. Together with its partner MDS Electric Srl, STS has implemented a comprehensive system for groundwater and surface water management in Romania.

Romania draws a major part of its potable water from surface waters such as the Danube, as well as from groundwater resources. A sound management of these natural resources is therefore of huge importance.

To safeguard potable water supply and to protect from flooding, the nation has invested in a comprehensive hydrological measurement infrastructure.

Figure 1: Groundwater measurement point 

In collaboration with its Romanian partner, MDS Electric Srl, over 700 data loggers and more than 350 data transmission systems have thus been installed throughout the country in recent years – also including remote areas. For this reason, the primary investment was in battery-operated measuring instruments, which monitor the current situation on the rivers of the Danube region and also the groundwater resources across the country.

Requirements-specific measurement solutions 

This was a complex undertaking, since each of the submersible probes and data transmission systems deployed required a different assessment and intervention to comply with their respective conditions. An automatic alarm function was also indispensable in this case, should predefined limit values be exceeded.

The permanent monitoring of water levels at important nodes across the potable water supply, as well as the rivers of the Danube region, hinges upon a multitude of requirements:

  • An automated and dependable data transfer via M2M protocol
  • Automatic alarm function when limit value is exceeded
  • Monitoring of water level and temperature, as well as ambient temperature in some instances
  • A server solution with functions for visualizing, evaluating and processing the measured data, as well as the integrated database
  • Easy installation and maintenance
  • On-site support service

For the implementation of this large-scale project, STS opted in pressure and temperature measurements for the DL/N 70 and WMS/GPRS/R/SDI-12 data loggers, or – depending upon requirement – the DTM.OCS.S/N digital data transmitter with Modbus interface to ensure highly precise water level measurement to a 0.03 percent accuracy at critical points.

In association with our local partner MDS Electric Srl, STS was able to realize the entire water level monitoring system from a single source. Each installation point was evaluated on-site by experts from MDS Electric Srl and STS, in order to install a custom solution at each of those individual measurement points. The long-term stability of the pressure measurement technology deployed is also guaranteed. The Modbus transmitter DTM.OCS.S/N excels in this area with an excellent long-term stability of less than 0.1 percent total error per annum. Because of its low energy consumption and robust design, this sensor performs largely maintenance-free for years on end.

Further advantages of the DTM.OCS.S/N in brief:

  • Pressure range: 200mbar…25bar
  • Accuracy: ≤ ± 0.15 / 0.05 / 0.03 % FS
  • Operating temperature: -40… 85 °C
  • Media temperature: -5…80 °C
  • Interface: RS485 with Modbus RTU (standard protocol)
  • Simple implementation in existing Modbus systems
  • Easy adjustment of span and offset

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