Industry Contribution: Nuclear against Ultrasonic Density Measurement


Image Courtesy: STI/Arenal

After a long time of research, development and preparation, companies STI/Arenal and Boskalis Nederland BV took on the challenge to compare nuclear and ultrasonic density meter for the dredging industry.

For demonstration purposes, Boskalis chose the vessel ZZ Rhenus working on the project Strandeiland near Amsterdam.

Technical solution

STI/Arenal mounted the Slurry Density Analyser (SDA) on the Boskalis vessel ZZ Rhenus in August and the test started on August 28, 2018.

During the demonstration, the meters were both logged several times.

Main target

Demonstrating the accuracy between a nuclear density meter and an STI/Arenal ultrasonic density meter, for a period of 3 months.

• Pipe diameter: 600 mm
• Pipe material: steel
• Density: 1-1.8 ton/m³
• Temperature: 12-20 ˚C

The aim of the research was to determine whether the STI/Arenal meter yields comparable results compared to the conventional meter. STI/Arenal also wanted to know whether the results are reproducible and therefore reliable in the longer term.

In this test, pure water forms the zero measurement. The density meters must always go to zero as soon as water is applied after a test. Both meters do well, but with still water the sensor of the STI/Arenal meter is no longer heated or cooled by the process. This is the reason that the measurement is progressing.

If a flow meter is switched on, the mass flow at that moment becomes zero and the density meter has no influence on the measurement. In all cases, the measurement results from both density meters follow each other. It is not easy to determine which meter is more accurate in this highly variable process.

What is clearly visible is that the STI/Arenal system reacts directly to changes in the sludge flow and the radioactive measurement only after a few seconds.

“We proved that there is no difference between the two measure methods. The density meter was used in combination with a ultrasonic flow meter and both measurements were shown on the digital cross meter in the wheelhouse of the vessel,” STI/Arenal said.

A running average has therefore been applied in the picture so that the meters can be compared better.

The STI/Arenal meters are made of silicon carbide (SSIC), the second hardest material on earth. Wear is therefore virtually excluded. Should there be some wear and tear that causes the design of the meter that it does not affect the measurements.

As long as there is no change in the physical properties of the sensor, no re-calibration is required. However, current sensors can age a bit internally (piezo elements).

It is therefore recommended to do a water calibration every month or when starting a new project. To this end, water is pumped through the pipe for two minutes. After this time, the operator can press the water calibration button. This makes the re-calibration of the sensor a quick and easy to perform operation.

– Arenal is the first and only producer of ceramic
sensors in the world.
– Ability to measure temperature and density.
– Extremely durable.

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