The couplant is the physical bridge between the ultrasonic probe and the material: without couplant there is no measurement. RODER SRL supplies two gels and two high-temperature pastes, for use from -30 to +520 °C.
- Types: gels and high-temperature pastes
- Gels: GEL-ACC-STD 0 / 80 °C, GEL-ACC-EXT -20 / 120 °C
- Pastes: PST-ACC-MHT -30 / +300 °C, PST-ACC-UHT +100 / 520 °C
- Pack sizes: 500 ml (gels), 170 g and 200 g (pastes)
- Compliance: RCCM
Without a good couplant, ultrasonic measurement is impossible: the air between the probe and the material reflects almost all of the signal and prevents the ultrasonic wave from entering the part. The couplant fills this physical gap, reducing the acoustic impedance mismatch at the interface and allowing optimal signal transfer.
RODER SRL supplies four ultrasonic couplants: two gels and two special high-temperature pastes. Our technical team is at your disposal to help choose the product according to the operating temperature.
The gels cover temperatures from -20 to 120 °C. For hot surfaces, the special pastes PST-ACC-MHT (from -30 to +300 °C) and PST-ACC-UHT (from +100 to 520 °C) are available, to be used with high-temperature probes.
Need help choosing the right product?
Why a couplant is needed
Ultrasound travels well in solids and in liquids, but almost not at all in air. The difference in acoustic impedance between air and metal is so great that 99.99% of the ultrasonic signal generated by the probe is reflected at the air-surface interface without penetrating the part. For this reason even the slightest surface irregularity or a microscopic layer of air can spoil the measurement.
Couplant solves the problem: it fills the micro-irregularities between probe and surface with a medium of intermediate acoustic impedance, ensuring that the ultrasonic beam enters the material without losses. Choosing the right couplant directly affects the sensitivity, repeatability and accuracy of the measurement.
The four couplants available
The range comprises four products, differing in temperature range and pack size:
GEL-ACC-STD
Yellow rust-inhibiting couplant gel, RCCM compliant. Standard temperature range 0 / 80 °C. 500 ml pack.
GEL-ACC-EXT
Blue corrosion-inhibiting couplant gel, RCCM compliant. Extended temperature range -20 / 120 °C. 500 ml pack.
PST-ACC-MHT
Special paste for ultrasonic coupling at medium temperature, -30 / +300 °C. Non-flammable and produces no fumes. RCCM compliant. 170 g pack.
PST-ACC-UHT
Special paste for ultrasonic coupling at very high temperature, +100 / 520 °C. Non-flammable and produces no fumes. RCCM compliant. 200 g pack.
How to choose the right couplant
- From 0 to 80 °C: GEL-ACC-STD gel
- From -20 to 120 °C: GEL-ACC-EXT gel
- From -30 to +300 °C: PST-ACC-MHT paste
- From +100 to 520 °C: PST-ACC-UHT paste
- Hot surfaces: pair the couplant with a high-temperature probe
Good practice in application
- Surface cleaning: remove oxides, dust and residues before applying the couplant
- Quantity: a generous drop is enough; avoid waste
- Repeatability: use the same quantity and the same settling time for comparative measurements
Typical applications
- Every thickness measurement with dual element corrosion probes
- Precision measurements with single element probes
- Flaw inspection with shear wave probes and wedges
- Bolt tension under the bolt head
- HT measurements on steam plant, heat exchangers and furnaces with high-temperature couplant
Frequently asked questions
Can I use oil or grease instead of couplant?
Technically possible for occasional measurements, but not recommended: oil and greases have a different acoustic impedance from an optimised couplant and can give less accurate readings. In addition, some greases contain additives that attack the seal of precision probes. Always use a couplant formulated for ultrasonics.
How long does a pack of couplant last?
How long it lasts depends on the intensity of use and the amount applied per measurement. A standard pack is typically enough for hundreds of measurements if used sparingly (one generous drop is enough). Always check the expiry date shown on the pack.
Are the high-temperature pastes also suitable at room temperature?
It depends on the product. PST-ACC-MHT is rated from -30 to +300 °C; PST-ACC-UHT is rated from +100 to 520 °C and is therefore not suitable at room temperature. For measurements at room temperature, the GEL-ACC-STD and GEL-ACC-EXT gels are used.
Request availability and a quotation: contact us stating the type of application and the quantity required.