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Articles

Silver Bullet Couplants – for inspections that are almost impossible without the right couplant.

Many UT applications require a specialty UT couplant.  For difficult inspections that require high acoustic impedance, shear wave, reduced surface noise, extreme temperature range or extended service life for sensors, we have the right couplant.

High Impedance Couplant: A high impedance couplant typically has an acoustic impedance above 3.5 M Rayls.  Water based couplants typically have acoustic impedances between 1.5 and 1.8 M Rayls depending on the Glycerin content (0% glycerin at 1.5 M Rayls, 12% glycerin at 1.8 M Rayls, 100% glycerin at 2.4 M Rayls). 

The advantage of a high impedance couplant is that more of the acoustic energy is transmitted between the transducer (or delay line) and test object and less is reflected and scattered at the surface of the test object.  This is particularly important when:

  • The test object surface is very rough (porous cast iron, scale, rough grinding).
  • The contact area for the delay line or transducer is small (pencil point probes measuring pit depths).
  • Materials such as concrete which are high impedance, scatter acoustic energy and often have a rough surface.

There are currently two options for water-soluble, high impedance couplants:

  • Z+ MV, a medium viscosity Glycerin based couplant (which has an operating range of 0 to 200°F; however, its viscosity increases quickly with temperature below 45°F.
  • Z+ fluid– does not contain Glycerin and maintains a fluid viscosity down to sub-zero temperatures.

Normal Incidence Shear Wave Couplant:

Not to be confused with angle beam generated shear waves (which rely on refraction of a longitudinal beam), normal incidence shear wave transducers propagate the shear wave with the transducer perpendicular to the test object and do not rely on refraction.  A normal incidence shear wave couplant requires a very high viscosity, high elastic modulus to perform acceptably.  Currently there is one commercially available water-soluble couplant that meets this requirement: Echo Shear Wave Couplant

Flow Meter and Sensor Couplant:

For permanent or long-term use, a flow meter couplant should resist creep, have good resistance to weather and chemicals as well as a broad temperature range.  Water-based couplants are suitable only for short-term flow metering applications. Echo 8 ZH is not water-based and is an excellent couplant for flow metering sensors.

Cryogenic UT Inspection:

CryoSoniX is the only ultrasonic couplant for use in cryogenic applications such as refrigerated ethylene. With an operating range of -200˚ to 60˚F (-129˚ to 16˚C), CryoSoniX enables repeatable and reliable inspections.

Phased Array Wedge Couplant:

Forever Wedge is an ideal couplant for use between phased array or angle beam transducers and the wedge.  Forever Wedge couplant won’t leach out, is impervious to water and couplants and when applied correctly, often lasts the life of the wedge or until it is replaced.  Forever Wedge eliminates phased array element drop out due to wedge couplant failure.

Looking for the right fluid for your AUT Inspections?

Echo’s automated ultrasonic testing fluids offer solutions for those who’ve encountered problems with other fluids. Often, fluids are too thick to pump, run off too fast, smoke too much, auto-ignite, freeze or vaporize so quickly that there’s no time to conduct the inspection.

With AUT fluids in multiple viscosities (thicknesses) spanning a broad range of temperatures, Echo has solutions to each of these problems. Several Echo AUT fluids are water-soluble, too, so they don’t leave a film on water when used at sea.

Echo AUT fluids have viscosities ranging from 125 to 5000 cps and covering temperatures from  -70° F to 1250° F (-57° C to 675° C).

The five AUT fluids listed below are arranged by increasing Operating Range:

Echo 4HT is a water-soluble fluid with an operating range of -70° F to 450° F (-56° C to 230° C). It has low toxicity and good surface wetting. Echo 4HT is slow drying and is compatible with a broad range of materials, including most metals, plastics and composites.

VersaSonic fluid is a plant-based, biodegradable fluid with low toxicity and an operating range of -10° F to 700° F (-23° C to 371° C). Above 400° F (200° C), VersaSonic works best when sprayed or pumped (discharged) at the point of use.

Echo 8HT  features minimal residue in a broad range of AUT and MUT ultrasonic flaw- and thickness-gaging applications, from -50° F to 800° F (-45° C to 425° C). The Echo 8HT line is compatible with all metals and most plastics. Echo 8 HT is available in three viscosities: grades 1, 4 and 10.

SpectrumGlide, a high-performance fluid for high-temperature testing, has a viscosity formulated to reduce runoff and provide longer dwell time at temperatures from -50° F to 730° F (-45° C to 387° C). SpectrumGlide was developed by Eclipse Scientific and is distributed under license by Echo.

EchoTherm Extreme fluid is the highest-temperature fluid couplant available. EchoTherm Extreme is a high-viscosity fluid that produces less smoke and minimal residue. It has the broadest operating range, from -40° F to 1250° F, and its auto-ignition point is above 1300° F (704° C).

No matter the testing environment or application, it’s likely that Echo Ultrasonics has — or can develop — just the right couplant. Give the Echo experts a call to find the right couplant for your needs or to request a sample.

ASNT Annual Conference a big success

Thanks to everyone who visited with us at ASNT in Nashville.

Couplant sample requests are being entered and we will be in touch soon.  We had many discussions regarding the use and success of EchoPure for Phased Array inspections.   EchoPure is the solution for phased array element drop out and the resulting difficulty in reproducing flaw indication.   The water-free formulation and strong coupling film of EchoPure provides a continuous film between the part and the transducer and resists “air gap puddling” which is common with couplants containing water.  

For more information, visit our EchoPure webpage or download the datasheet from Resources.