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NDT Accessories
Couplants
Couplants are the gels, pastes and liquids placed between an ultrasonic probe and the test surface so that sound can pass into the part. Air blocks ultrasound almost completely at the frequencies used in NDT, so even a thin film of air under the probe stops the measurement. The first product listed here is Magnaflux Ultragel II, a medium-viscosity general purpose gel rated from -23 to 99 °C. Seven Star LLC in Oman can also source other ultrasonic couplants on request for thickness gauging, flaw detection and bolt tension work.
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About Couplants
Couplants are the gels, pastes and liquids placed between an ultrasonic probe and the test surface so that sound can pass into the part. Air blocks ultrasound almost completely at the frequencies used in NDT, so even a thin film of air under the probe stops the measurement. The first product listed here is Magnaflux Ultragel II, a medium-viscosity general purpose gel rated from -23 to 99 °C. Seven Star LLC in Oman can also source other ultrasonic couplants on request for thickness gauging, flaw detection and bolt tension work.
Types of couplant in ultrasonic testing
General purpose couplants are water-based gels, often with glycol or glycerin, in several viscosities. Thin liquids suit smooth surfaces and scanning. Thick gels stay in place on rough, vertical or overhead surfaces. High temperature couplants are formulated to resist evaporating on hot pipe. Normal-incidence shear wave probes need a special, very viscous couplant, because ordinary liquids do not transmit shear waves.
Choosing an NDT couplant
Match the couplant to surface temperature, surface roughness, orientation and the material. For austenitic stainless steel, nickel alloys and titanium, codes such as ASME Section V limit halogen and sulfur content, and a batch analysis certificate is normally required. Consider cleanup too, since residue can interfere with painting or welding.
What to tell us
Send the surface temperature range, the material, the quantity and container size, and any contaminant limits in your procedure. Inspection teams elsewhere in the GCC can ask in the same way.
What to include in your inquiry
These details let us quote the right item the first time.
- Material and thickness range
- Application (corrosion survey, weld inspection, bolt tension)
- Instrument model, when ordering probes or accessories
- Transducer frequency and type
- Standards the inspection must follow
Missing some of them? Send what you have. A nameplate photo or an old part number is enough to start.
Brands in Couplants
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Request a Quote for Couplants
Looking for a specific model, part number or brand in Couplants? Send us your requirements and quantities. Seven Star LLC sources genuine industrial equipment for customers across Oman and the GCC and replies with a formal quotation.
- Genuine OEM products
- Supply across Oman & the GCC
- Formal quotation from our sales team
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Frequently Asked Questions
What is a couplant and why is it used in ultrasonic testing?
A couplant is a liquid, gel or paste that fills the microscopic gap between the probe face and the part. Ultrasound at testing frequencies is almost entirely reflected at a boundary with air, so without couplant no usable signal enters the material. The couplant displaces the air and provides a continuous path for the sound. It has to wet both surfaces and stay in place for the duration of the reading.
Can I use water, oil or grease as a couplant?
Yes, in many cases. Water works on smooth horizontal surfaces and is the couplant in immersion testing. Oil and grease couple well and stay on vertical surfaces, but they are harder to clean off and may contaminate surfaces due for painting or welding. Purpose-made gels give consistent viscosity, usually include corrosion inhibitors and come with known chemistry, which matters when a procedure limits contaminants.
Which couplant should be used on stainless steel and nickel alloys?
Use a couplant with controlled, low levels of halogens (chlorides and fluorides) and sulfur. These elements can promote stress corrosion cracking or embrittlement in austenitic stainless steels, nickel alloys and titanium. Codes such as ASME Section V require analysis of the couplant for these contaminants on such materials. Ask for the batch analysis certificate from the couplant manufacturer and keep it with the inspection record.
What is different about high temperature couplant?
Ordinary gels boil or dry out within seconds on hot metal, which breaks the acoustic path and can leave residue. High temperature couplants are formulated to remain fluid and stable over a stated temperature band. Each product has its own upper limit, and some have an auto-ignition temperature to respect, so select by your actual surface temperature and read the safety data sheet before use.
Does couplant viscosity affect the thickness reading?
It affects how reliably you get a reading more than the value itself. On rough or pitted surfaces a thick gel fills the valleys and keeps the probe coupled. On smooth surfaces a thin couplant gives a thinner, more uniform layer, which matters for precision gauging where a thick couplant film can add a small error. Use the same couplant for calibration and measurement.