High Temperature Couplants
During phased array testing, element dropout can be a problem. Common causes include dead elements in the transducer or a failure of the wedge-to-transducer or wedge-to-inspection-part coupling.
Let’s look at each of these coupling failures in detail before offering some solutions for each of these PA testing issues.
Wedge-to-transducer coupling failure is often partial and typically involves multiple adjacent elements. While minimal phased array element dropout at the edges of the array can often be tolerated, failure of transducer coupling where multiple adjacent elements are not coupled into the wedge, particularly away from the array edge, will impact inspection quality, reproducibility and reliability. This dropout is often not detected, and the technician continues scanning unaware of increased side lobes (or grating lobes) and altered beam steering characteristics.
The couplant used between the transducer and the wedge is critical to reproducible inspections. When the couplant is exposed to water or to the couplant used on the parts being inspected, leaching of the wedge couplant can occur. Heating and cooling can cause thermal expansion and contraction of the couplant, tearing apart sections of the wedge coupling film. Some wedge couplants can partially evaporate over time, resulting in progressive failure of the coupling film.
To prevent problems with transducer-to-wedge coupling in phased array inspections, you need a wedge couplant with the following properties:
- impervious to water and other couplants, to prevent leaching of the wedge couplant around the perimeter;
- strong film former, to prevent isolated air pockets due to localized coupling film separation;
- high viscosity (over 3,000 cps), to ensure uniform coating and thickness independent of the surface and the mating characteristics of the wedge and transducer;
- resistant to evaporation or vaporization over the temperature range in which the PA transducer will be used and stored;
- thermal stability to prevent expansion and then contraction of the coupling film, resulting in film separation;
- compatibility with materials used in phased array transducer construction and wedge materials;
- long lasting so that it does not need to be replaced for the life of the wedge; and
- promotes easy replacement of wedges, without sticking or bonding between wedge and transducer, regardless of storage conditions.
Wedge-to-test-object coupling failure caused by couplant film failure results in acoustic reflection into the wedge, generating false reflections and noise. Couplant film failures of this nature are usually partial and continually change in location and configuration as the transducer assembly moves.
Failure of the couplant between the wedge and the test piece is most often due to low strength and fragile film formation. One example is gel couplants of the acrylic polymer (Carbopol) type. These polymers, which were originally developed for the hairstyling industry, have weak film-forming characteristics and are subject to collapse of the coupling film when exposed to corrosion or marine salts.
Couplants that have a water component in the formulation also may have weak film-forming properties. While water solubility is a desired feature in many applications, water incorporated into the couplant formulation serves mainly to lower cost. It does not promote coupling film strength. Couplants that contain water also can be subject to film failures from vaporization or the formation of ice crystals on the test site.
Echo Ultrasonics offers solutions to problems with both wedge coupling and inspection-object coupling in phased array inspections.
- Forever Wedge Couplant addresses failure in coupling the PA transducer to the wedge. Forever Wedge Couplant will remain in place for the life of the wedge and is impervious to water, other couplants, heat, thermal expansion and contraction, and evaporation. It also can overcome mechanical issues, such as mating or surface roughness of the wedge-to-transducer interface.
- EchoPure is a water-free couplant that provides a strong, uniform coupling film that eliminates dry spots between the wedge and the part being inspected. EchoPure also meets the water-free-couplant requirements for inspecting P91 steel prior to heat treatment.
Free samples of EchoPure and Forever Wedge Couplant are available for your evaluation.
VersaSonic is a leading high temperature couplant, but … read how Caterpillar and power generation equipment manufacturers are using it.
Caterpillar Inc., the well-known equipment and engine manufacturer, has approved VersaSonic for use on its CAT equipment. Caterpillar is distributing VersaSonic through its dealers worldwide for UT thickness gauge inspections in harsh environments, from sub-zero to very hot conditions. VersaSonic is being distributed as Caterpillar part number 545-8721.
Power generation equipment manufacturers have approved VersaSonic for its compatibility with electrical wiring insulation for use in their power generation rotor inspections. VersaSonic does not contain water, is non-corrosive and is low in toxicity.
Acuren, Team Industrial Services, Mistras, IRIS NDT and many other inspection companies select VersaSonic for its high temperature properties and two viscosities:
- high-viscosity VersaSonic for hot piping over 350° F (177° C) and for direct placement on the transducer, and
- medium-viscosity VersaSonic for spreading on parts and at temperatures under 350° F and as low as -10° F.
The nondestructive testing industry chooses VersaSonic for its technical performance. VersaSonic has a lower rate of vaporization and evaporation above 350° F than competitive couplants, resulting in longer inspection windows and less need for reapplication of the couplant. Tests of weight loss from evaporation over time have shown that VersaSonic loses less than 1 percent of its original weight by the time the product has reached 392° F, while competing products can lose twice that amount.
VersaSonic is plant-based and biodegradable. It does not contain peanut oils, tree nut oils or silicones. Additionally, VersaSonic provides excellent corrosion inhibition for steel and cast iron and it can be left in place providing it won’t interfere with subsequent operations such as painting or electroplating. VersaSonic can be removed with a wipe from a rag or cloth; for complete removal, dish detergent and water or Echo 4HT can be used.
Echo Ultrasonics has recently become the exclusive distributor of SpectrumGlide AUT-NDT Fluid Couplant in the U.S. and Canada.
SpectrumGlide, developed by Eclipse Scientific, 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).
The addition of SpectrumGlide gives Echo Ultrasonics a full range of automated ultrasonic testing fluids, with viscosities ranging from 125 to 5000 cps and covering temperatures from -70° F to 1200° F (-57° C to 649° C).
SpectrumGlide’s formulation results in faster and more efficient testing by allowing it to remain on pipes, tanks and other surfaces longer without draining off. Because it can be used in testing environments up to 780°F (415°C), it’s a versatile fluid for high-temperature AUT applications.
AUT uses automatic equipment to run a variety of inspections in numerous industries, from corrosion mapping to thickness gauging to weld inspection. For example, AUT is an efficient and accurate method for analyzing the integrity of pipeline welds in the oil and gas industry.
50 years of developing and manufacturing the world’s leading NDT ultrasonic couplants enable Echo Ultrasonics to provide customers with the most cost-effective, highest-performance and safest couplants for each application. Let us recommend and provide samples of the right couplant with today’s technology for your specific needs.
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.
Vaporization of VersaSonic™ vs Sono 600®
The above plot is a technical representation of why VersaSonic (top line) outperforms Sono 600 (bottom line). The plot depicts the weight loss of each couplant due to vaporization over time at 200°C (392°F). Sono 600 loses significantly more mass and vaporizes faster than VersaSonic. Vaporization produces gas bubbles which both attenuate and scatter ultrasound as well as degrades the rheology of the product (coupling doesn’t last as long, dries faster and gets sticky or tacky sooner).
While many Echo customers that have switched to VersaSonic from Sono 600 have observed these characteristic in practice, this test demonstrates the technology behind the experience.
VersaSonic is the ideal high temperature ultrasonic couplant when working under 750°F (400°C). The response is instant as there are no plastic polymers in VersaSonic that need to melt before transmission occurs. At higher temperatures (above 350°F / 177°C) its useful service life is longer than competitive couplants. The auto-ignition temperature for VersaSonic is 788°F (420°C). VersaSonic is available in two viscosities:
- High Viscosity – ideal for spot inspections
- Medium Viscosity – best for spreading
For more information, samples and ordering information, click here or call 360.617.9121.
We’ve expanded our line of Echo 8HT fluid UT couplant to include three additional viscosities. Performance of a broad range of AUT and MUT ultrasonic flaw and thickness gaging applications from -50°F to 800°F (-45°C to 425°C) is possible with these four grades, with minimal residue and great signal to noise ratio.
Grade 1 is the lowest viscosity fluid (100 cST) for long or small diameter lines and quick spreading.
Grade 4 is Echo’s standard viscosity fluid (400 cST) and is usually a good compromise between pump ability and run-off at the transducer.
Grade 6 is a higher viscosity fluid (850 cST) that minimizes run-off at the transducer, however, requires system “pump ability” testing.
Grade 10 is a very thick fluid (5,000 cST – honey like) for MUT. It spreads easily over large hot surfaces, stays in place and leaves minimal if any residue.
Introduced in the mid 1970’s by Aerotech / Krautkramer Branson and sold by GE Inspection Technologies for decades, HiTempco has been the standard of performance in silicone based ultrasonic couplants. With a broad temperature range of -50°F to 775°F (-45°C to 412°C), its applications range from high temperature thickness gauging and flaw detection to ambient and low temperature coupling where no corrosion, broad material compatibility, long service life and low toxicity are considerations.
- Very high viscosity
- No residue
- Strong corrosion inhibition
- Non-toxic, non-irritating
- Low environmental impact.
- Contains no perfluorocarbons, peanut or tree nut oils.
-50°F to 775°F (-45°C to 412°C)
Flash Point and Auto-Ignition Temperature
Flash Point: Cleveland Open Cup 250°F
Auto-Ignition Temperature: 820°F
Instantaneous ultrasonic response (does NOT contain plastic powders which delay ultrasonic conduction and result in difficult-to-remove residues). Excellent corrosion inhibitor. Provides non-toxic, long-term corrosion inhibition for steel and cast iron and is compatible with other metals and most plastics. HiTempco may be left in place unless it will interfere with subsequent manufacturing operations such as painting or electroplating.
Removal: wipe with paper or cloth rag. If complete removal is required, dish detergent and water or a chemical degreaser can be used.
Contact us today for complementary samples: firstname.lastname@example.org or 360.671.9121
Click here to view an article on Auto-ignition from Ultrasonic couplants in the latest Inspectioneering Journal. Free access has been granted due to the safety concern.
You may be aware that VersaSonic® has superior performance from -10 to 750°F, however, did you know:
- VersaSonic is available in medium viscosity for optimal spread-ability and high viscosity to “stay in place” on a transducer, pipe or overhead surface.
- VersaSonic is available in open-top 1 and 5-gallon pails (5-gallon dispensing pump included at no charge), 1 gallon and quart cubitainers.
- VersaSonic is a versatile broad temperature couplant. The world’s largest producer of power generating equipment has standardized on VersaSonic for use at ambient temperatures due to its compatibility with their electronic components.
- Refineries and heat treatment plants use VersaSonic because its useful service life is up to three times longer than competitive couplants at temperatures above 350°F.
Have a job where you need to spread the couplant in some areas but need it to stay in place in others? Try our quart dual pack of both viscosities.
Testing above 750°F? EchoTherm and EchoTherm Extreme are the only ultrasonic couplants with operating ranges above 850°F.
Check out our complete line of high temperature couplants online:
Our Mission at Echo Ultrasonics is to provide the highest performance ultrasonic couplants based on today’s chemistry and compliant with world Regulatory Guidelines.
Intertek Scientific & Regulatory Consultancy was retained to conduct a REACH assessment / CLP Evaluation for all Echo Ultrasonics high temperature ultrasonic couplants. Intertek determined that there is NO CLP Classification or Special CLP Labeling required.
VersaSonic®, EchoTherm™ and EchoTherm™ Extreme offer optimal performance, safety and regulatory compliance.
Request samples today: https://www.echoultrasonics.com/resources/free-samples/