Important Considerations for Couplant Selection
Couplant selection is a critical factor to insure reliable, repeatable UT inspection results and to optimize productivity.
Couplant is required due to the acoustic impedance mismatch between air in the interface with the transducer and the test object. If there were no couplant, nearly all of the energy from the transducer would be reflected back into the transducer and very little would be transmitted into the test material.
Couplant selection includes operating range, acoustic properties, viscosity, evaporation rate, environmental restrictions, corrosion inhibition, removal and cost.
- Performance: higher performance couplants can provide extended drying time, stronger coupling films and higher acoustic impedance. Seldom are all three of these technical features available in the same product, therefore, it is helpful to choose the most important one or two.
- Operating Range: the temperature of the part being inspected and the operating range of the couplant are critical factors in selecting a couplant. Use of a high-temperature couplant outside the operating range, especially in a port or enclosed environment can result in an auto-ignition (fire without an ignition source). Use of a couplant below the operating range can result in ice crystal formation on the part with acoustic scattering and noise.
- Cost: for general inspections, costs can often be reduced using powdered couplants or bulk economy couplants. Sometimes the lowest cost couplant is economical, in other cases it requires longer inspection times (due to couplant drying) re-inspection (due to signal variation) and preparation (such as mixing powder couplant). The most economical couplant has the correct operating range, allows for a complete inspection without re-application and has a film strength appropriate for the type of scanning or spot inspection.
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.
Phased Array Wedge Couplants:
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.
EchoPure is an ideal couplant for phased array scanning due to its strong film strength, slow drying characteristic and very broad temperature range. Element drop out with phased array transducers can occur from dead elements in the transducer or a failure of the wedge-to-transducer or wedge-to-inspection part coupling. While minimal PA element drop out at the edges of the array can often be tolerated, failure of transducer coupling where multiple adjacent elements are not coupled into the wedge, will impact inspection quality, reproducibility and reliability. This drop out is often not detected and the technician continues scanning unaware of increased side lobes (or grating lobes) and altered beam steering characteristics. EchoPure forms a strong film to prevent isolated air pockets due to localized coupling film separation.
High Temperature Couplant: EchoTherm Extreme: is the only high temperature couplant with an auto-ignition temperature above 1300°F and an operating range up to 1250°F / 675°C. It is safe for use in all environments for all high temperature inspections including ports and under insulation.
High Impedance Couplant: 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 contact area for the delay line or transducer is small (pencil point probes measuring pit depths).
- The test object surface is very rough (porous cast iron, scale, rough grinding and fiberglass).
- Materials such as concrete which are high impedance, scatter acoustic energy and often have a rough surface.
Echo Z+ has an acoustic impedance above 3.5 M Rayls. Water based couplants typically have an acoustic impedance between 1.5 and 1.8 M Rayls depending on the Glycerin content.
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.
Normal Incidence Shear Wave Couplant: A normal incidence shear wave couplant requires a 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 and ultimately be easily removed. 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.
At Echo Ultrasonics, we have been helping people select the best couplant for specific applications for over 50 years. Give us a call or email with your requirements and we will help you select the best couplant for the job.
API Subcommittee on Inspection and Mechanical Integrity to address the auto-ignition of NDT Ultrasound Couplants
As recently published in Inspectioneering Journal:
“The API Committee on Refinery Equipment (CRE) made a recommendation that SCIMI address the auto-ignition of NDT ultrasound couplants by including new paragraphs in the upcoming rewrites of API RP 572 (Inspection of Pressure Vessels) and API RP 574 (Inspection Practices for Piping System Components). These paragraphs will incorporate actions such as the following:
- Check the product label for the manufacturer’s operating range. If the operating range is not on the container, do not proceed, nor provide the product to inspectors.
- Know the surface test temperature where the couplant will be applied. This is of highest importance in ports and restricted areas.
- Provide access to a current product Safety Data Sheet listing the operating range and auto-ignition temperature to the inspector.
- Train inspectors in the mitigation of risk of couplant auto-ignition in high temperature inspections”
All of Echo Ultrasonics’ high temperature couplants are clearly labeled on each container with the operating range and auto-ignition temperature and are therefore in compliance with these recommendations.
Complete details can be found in the current issue of Inspectioneering Journal.
Save Time, Reduce Cost and Improve Safety & Performance with Echo Ultrasonics UT Couplants
Echo Ultrasonics can help you save time by ordering direct. We stock all couplants in all container sizes and offer same day shipping with worldwide delivery.
Reduce Cost:
Echo’s commitment is to provide the highest performance and safety profile ultrasonic couplant at a fair price, or 10% less than the lowest competitive price for a similar performance couplant.
Selecting the best couplant for your application can reduce your costs. Along with Echo’s lowest cost guarantee, we can help you to select the best couplant to optimize:
- price vs. performance
- longer inspection windows
- less re-application required
- broader operating range
- no residue to clean up later
Improve Safety and Performance
- SuperSoniX™: is Echo’s highest performance water-based couplant that doesn’t thin with corrosion salts and reduces the need for re-application.
- EchoPure™: is ideal for phased array (reduces artifacts) and very cold or warm inspections (-60° to 350° F / -51° to 176° C).
- EchoTherm™ Extreme: Eliminates auto-ignition risk and is safe in ports above 775°/ 412°C. Less smoke and no residue.
- VersaSonic®: is the most versatile ultrasonic couplant with two viscosities; optimizing inspections from high temperature to working in mud and snow (-10° to 750°F / -23° to 371°C).
- AUT Fluids: Echo has the broadest line of AUT fluids with several viscosities to optimize pumpability and reduce run-off.
If you haven’t tried our couplants, contact us today to speak with one of our experts. Complementary samples available.
SuperSoniX™ – A new UT Couplant with a Historic Name
In May of 1940, Floyd Firestone, a Professor in the department of Physics at the University of Michigan, filed US patent 2280226 in which he described an instrument for the detection of flaws and measuring thickness in metal objects. Dr. Firestone used the term “Supersonic Vibration Waves” to describe what we now refer to as pulse-echo Ultrasound Testing (UT).
The term “Supersonic Inspection” was used in reference to UT officially until the first manned aircraft flight by USAF Captain Chuck Yeager exceeded the sound barrier of 768 mph in October of 1947. Captain Yeager’s flight in the Bell X-1 “Rocket plane” became known as supersonic flight. Gradually the term Ultrasonic Testing replace d Supersonic Testing in NDT.
Echo UltraSonics® new water-based gel couplant, SuperSoniX, is named in honor of Dr. Firestone and his work which gave rise to our world of UT.
SuperSoniX is our third-generation acrylic polymer water based couplant that improves on the electrolyte stability and reduces the tendency for the polymer to collapse when exposed to corrosion or marine salts. In practice this means less reapplication of couplant during a test procedure, especially on objects that are exposed to the environment.
SuperSoniX offers several benefits, including; a broader operating range, a slower evaporation rate, a longer drying time, improved stability against corrosion salts and is environmental and operator friendly.
Couplant Selection
While many couplants will couple sound and perform adequately for the same inspection, often one will deliver performance that will make a significant improvement on inspection reproducibility and defect detection (the #1 goal of UT). The right couplant can minimize couplant re-application during an inspection, reduce total time for the inspection and lower cost. Let us recommend the most appropriate couplant for your application and temperature range.
More Information
Contact Marian (360) 671-9121 or marian@echoultrasonics.com) for more information and free samples. We have over 50 years of history developing and manufacturing most of the couplants in use yesterday and today and can help in selecting the best couplant for your specific application.
VersaSonic® – A better alternative to Sono® 600
VersaSonic is the most versatile couplant with UT applications including:
- High temperature inspections – up to 700°F / 371°C
- Extreme weather conditions – rain, snow, mud and sleet
- Freezing temperatures down to -10°F / -23°C
- Power generation equipment – insulation compatible
- Best corrosion inhibition of all couplants
VersaSonic is available in two viscosities to optimize application:
- Medium viscosity for spreading on the inspection part and for lower temperature inspections
- High viscosity for placing directly on the transducer, overhead and vertical inspections
Peanut allergy concern for inspectors or their families? No problem. VersaSonic does not contain peanut oil.
VersaSonic has a lower vaporization rate than Sono® 600, leading to:
- Longer inspection windows
- Less re-application
- Reduced couplant use
The below graph shows weight loss from vaporization over time for VersaSonic (dotted line above) and Sono 600® (solid line below) at 200°C. (Independent commercial laboratory analysis)
Let us prove to you that Echo has a better high temperature couplant solution for safer, faster inspections. Request free samples today:
https://www.echoultrasonics.com/resources/free-samples/
360-671-9121
Selecting the Correct High Temperature UT Couplant
When performing UT inspections at elevated temperatures, it is critical to select the correct couplant, both for performance and safety. Thickness gauging and corrosion mapping are often conducted at temperatures between 500°and 1000°F (260° and 538°C) where auto-ignition may occur. Ultrasonic transducers and instruments capable of operating at temperatures up to 950°F (510°C) are routinely used, and development programs are targeting new designs with capabilities up to 1100°F (593°C).
Auto-ignition of ultrasound couplants has increased exponentially over the past decade due to higher temperature inspections, such as in heavy crude refining, and due to the extensive use of inspection ports. The risk to inspectors and facilities, as well as the liability auto-ignitions impose can be reduced or eliminated by a few steps:
- Make certain all high-temperature ultrasonic couplants are labeled with the current manufacturer operating range and that inspectors are aware of the range.
- Check the temperature of the part, especially in ports and confined areas, before inspecting. (Note: In confined spaces and inspection ports the temperature can be approximately 150˚F higher than on exposed pipe.)
- Select a couplant labeled for the intended operating range.
- Request and post the below adhesive backed sticker in a location where inspectors have access. Copies of the sticker are available at no charge by contacting 360.671.9121 or marian@echoultrasonics.com.
Elimination of auto-ignition of ultrasonic couplants is one of the lowest cost, highest benefit actions you can take to protect inspectors, facilities and to reduce liabilities.
The operating range of Magnaflux/Sonotech Sono® 1100 has been reduced to 700 to 775°F with a restriction for use in ports to under 455°F (below the operating range of the couplant). A better replacement is EchoTherm Extreme with an operating range of -40 to 1250°F with NO limitations for port, confined space or under insulation UT inspections.
All Echo Ultrasonics high-temperature couplants are labeled with the operating range and auto-ignition temperature. Echo’s couplant line includes:
Two couplants with an auto-ignition temperature above current UT equipment capabilities, no operating range restriction for ports, confined spaces or under insulation UT inspections:
- EchoTherm Extreme: -40 to 1250°F (-40 to 675°C):
- EchoTherm: 200 to 1000°F (93 to 538°C)
Two couplants with broad operating ranges, but require attention to the temperature in confined spaces and ports as the temperature can be approximately 150°F higher than on exposed pipe.
- HiTempco: -50 to 775°F (-45 to 412°C)
- VersaSonic: -10 to 700°F (-23 to 371°C)
Let us prove to you that Echo has a better high temperature couplant solution for safer, faster inspections. Request free samples today.
AUT Fluids: It’s all about the vaporization rate.
Determining the best AUT fluid for an application involves several factors:
- Maximum temperature of test object (or under insulation)
- Viscosity must be within the capability of the pump:
This decision includes knowing the viscosity at the minimum temperature of the fluid reservoir and supply lines and the maximum length of the line from pump to AUT device. A starting point for this determination:
|
Line Length |
Maximum Viscosity |
Fluid |
|
50’ or less |
800 cps |
SpectrumGlide VersaSonic Fluid |
|
100’ or less |
400 cps |
Echo 8 HT grade 4 |
|
200’ or less |
150 cps |
Echo 8HT grade 1 EchoPure Fluid |
Selecting the highest viscosity fluid that meets the pump and line capabilities results in the longest fluid dwell time and the best overall performance.
- Vaporization rate: All AUT fluids vaporize. Most fluids will perform satisfactorily until 5% of their weight has been converted to vapor. The fluid vaporization rate is a function of time and temperature.
The plot below demonstrates weight loss from vaporization on the Y axis and time as the X axis for two AUT fluids at 387°C / 728°F.
During the initial five minutes of exposure to the high temperatures, there was no detectable vaporization. At six minutes, vaporization increased exponentially and by 10 minutes one of the fluids had lost approximately 35% of its weight and the other had lost 15% of its weight due to vaporization.
Both of these fluids are suitable for AUT when the fluid is pumped to the transducer in that less than one minute is required for the fluid to support the acoustic parameters of the inspection. However, if the fluid is sprayed on the test object with a hand sprayer, the ability of the fluid to support the inspection will depend on the spraying and test occurring in less than a 5 minute window. After 5 minutes, neither fluid illustrated above will support an ultrasonic inspection.
Often a fluid that will perform for AUT when the fluid is pumped to the transducer will not perform when the fluid is sprayed onto the test object. In many instances, vapor will be visible around the AUT crawler and on the part; however, this vapor occurs after the ultrasound coupling time requirement.
The rate and volume of fluid delivery and the viscosity will also effect the vaporization rate. In general, a higher viscosity fluid, a faster rate of delivery and a greater fluid volume yields a lower vaporization rate. Often less expensive AUT fluids can be used by increasing the flow rate of the fluid. Clouds of vapor may form quickly; however, the key is having vapor occur after the required acoustic time window.
The following table lists each couplant suitable for the temperature and application method:
|
Temperature |
Pump |
Spray |
|
-60 to 350°F |
EchoPure Fluid |
|
|
450°F |
VersaSonic Fluid, Echo 8HT, SpectrumGlide |
Echo 8HT, VersaSonic Fluid |
|
650°F |
VersaSonic Fluid, Echo 8HT, SpectrumGlide |
Echo 8HT Grade 1 & 4 |
|
700°F |
Echo 8HT, SpectrumGlide |
|
|
800°F |
Echo 8HT |
|
What are Echo’s high-temperature AUT fluid options?
EchoPure Fluid: This glycol formulation has a reduced evaporation rate, is usually the least expensive option, is water soluble and covers very cold AUT down to -60°F (-51°C). Suited for pumping applications up to 350°F (176°C).
VersaSonic Fluid: This is a plant-based oil formulation. All plant based oil AUT fluids will smoke as well as vaporize and will leave a varnish or film on the surface. Suited for applications up to 700°F to pump, 450°F to spray.
Echo 8HT / SpectrumGlide: Silicone based fluids have the following advantages:
- Viscosity is relatively constant with temperature compared to other AUT fluids and is available in very low to very high viscosities to optimize pumpability versus dwell time.
- Minimal or no residue
- Less smoke than plant based oils
Silicone based fluid options include:
Echo 8HT: This fluid pumps easily, is an excellent lubricant and is compatible with all metals and most plastics. Suited for applications up to 800°F to pump, 650°F to spray.
Grade 1 – low viscosity (125 cps) – best choice for lines over 100’
Grade 4 – medium viscosity – best choice for 100’or less lines (400 cps)
Grade 10 – very high viscosity to be manually applied (brush). Cannot
be pumped or sprayed, very slow to run off. An alternative to high temperature gel couplants.
SpectrumGlide: The is the highest performance AUT fluid with a medium-high viscosity, best for lines 50’ or less, for applications up to 700°F to pump.
Still have questions? Give us a call. 360-671-9121
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.
Echo Direct: The best way to get the right couplant, right on time
Why buy UT couplants directly from Echo Ultrasonics? We provide UT Solutions.
With more than 50 years of experience manufacturing ultrasonic couplants, and having developed most of the ultrasonic testing couplants on the market today, the personnel at Echo Ultrasonics are experts in couplant selection. On staff, we have a metallurgist with ASNT Level III certification dedicated only to ultrasound couplants.
Echo personnel are committed to identifying the best couplant at the best price and are willing to go to great lengths to satisfy customer requirements. At other companies, couplants are a business. At Echo Ultrasonics, couplants are our passion.
Consider these examples:
- At 7:00 a.m., a customer called needing customized packaging for a high-temperature phased array inspection by 10:00 a.m. the next day. Because Echo has inventory of all couplants in stock, we were able to respond quickly, repackaging the needed couplant and shipping it for delivery at 7:57 a.m., hours before it is needed.
- A customer called at 8:30 a.m. on a Friday. His inspection team had been called to an emergency inspection in Africa, and they were to depart on Sunday. The customer, located remotely, had no local couplant source, and his team needed the couplant when they arrived in Africa on Monday morning. The Echo Team was able to put together couplant for the inspectors to pack in their luggage. With an overnight shipment and a Saturday delivery, the inspection team was able to successfully perform their inspection with the optimal UT couplant.
At Echo Ultrasonics, customer service isn’t a buzzword. We make certain our customers’ needs are met. That’s one reason a live representative answers the phones at Echo 24 hours a day, 7 days a week.
It’s also why we work hard to develop custom specialty couplants in response to our customers’ needs. Consider these custom couplants we’ve developed over the past two years:
- CryoSoniX is the only couplant in the world available to work at temperatures as low as ‑200 °
- EchoTherm Extreme is the only couplant in the world that can safely operate up to 1250 °
- Forever Wedge is a phased array wedge couplant that facilitates more reproducible inspections, fewer artifacts and longer wedge coupling.
- EchoPure is an ideal couplant for phased array inspection and reduces noise and artifacts from couplant failure between the wedge and test object.
Our goal at Echo Ultrasonics is to get you the right product at the right price, when and how you need it. Why buy UT couplants directly from Echo Ultrasonics? We provide UT solutions.
Right Product
- Formulated for specific applications.
- Product performance guarantee.
- 50 years of experience developing and manufacturing ultrasonic couplants.
Right Price
- Lowest price guarantee.
Right Delivery
- Need it overnight to a hotel room? International delivery? We can make that happen.
Right on Time
- 24/7 live telephone response.
- Emergency inspections? Foreign countries? Overnight shipment? We are here to help.
Right Availability
- All couplants in stock for immediate, same-day shipment.
Echo Direct: We love challenges. Let us help you optimize your inspections with the right couplant delivered to you at the right time.
GE approves Echo Glycerol for CFM56-7B engine fan blade inspections
Echo Ultrasonics is approved by GE as a supplier of Glycerol for the inspection of CFM56-7B engine fan blades in accordance with SB 72-1033.
Echo’s GE-approved Glycerol Echo Lot 205 is available in 16-oz / 500 ml bottles for overnight delivery worldwide. To order, contact Echo Direct 24/7 at 360-671-9121 or sales@echoultrasonics.com. Part number GLY-16, batch #205.
As noted in the National Transportation Safety Board’s May 3 investigative update of the engine failure on Southwest Airlines flight 1380, CFM International issued Service Bulletin 72-1033 on April 20 recommending ultrasonic inspections of fan blades of CFM56-7B engines with more than 30,000 cycles. The Boeing 737 on flight 1380 was powered by engines from CFM International, which is a joint company between GE Aviation and Safran Aircraft Engines.
By the end of August, CFM International also recommends inspections for fan blades with 20,000 cycles. When other fan blades reach 20,000 cycles, they also should be inspected, according to the service bulletin. After the first inspection, it is recommended that inspections are repeated every 3,000 cycles (typically, about two years in airline service).
Glycerol Echo Lot 205 from Echo Ultrasonics has been approved by GE Aviation for this inspection work.
Contact Echo Ultrasonics for more information and to order Glycerol Echo Lot 205 for GE fan blade inspections: 360-671-9121 or marian@echoultrasonics.com.
