Specification Conformance
ASTM, ASME, API, AWS, and OEM compliance may be required of the couplant depending on the specification. Our Ultrasonic Couplant Comparison chart shows an overview of specifications for each Magnaflux couplant product, but please refer to the individual product data sheet for a full list.
Specifications may have a maximum limit on halogen and sulfur content for the couplant. Certain industries may have lower limits. Magnaflux tests every batch of couplant for halogens and sulfur content and can provide the certifications for a specific batch.
Corrosion protection can be a factor as well, particularly for sensitive alloys and/or long-term exposure applications, such as flow metering. Ultragel II, Sono 600, and Pyrogel offer excellent long-term corrosion protection.
Temperature Range
For high-temperature ultrasonic testing, such as thickness gauging, it is important to use a couplant specifically formulated to hold up in high temperatures. General purpose couplants will not transmit ultrasonic energy at high temperatures and may burn or ignite.
It is important to never use a couplant at a temperature above the auto-ignition temperature. The auto-ignition temperature is the lowest temperature at which the material will spontaneously ignite without an external source of ignition.
Viscosity, being temperature dependent, should also be considered when choosing a couplant for a given temperature range. A couplant will become less viscous at higher temperatures.
Viscosity & Coverage
Viscosity is important in determining the coverage a couplant achieves depending on the type of part being tested and its surface texture. Rough parts may require a more viscous material to ensure coverage, while smooth parts can be covered well with thinner couplants.
Orientation of the testing can also dictate viscosity requirements. Testing on vertical or vertically inclined surfaces may require a high viscosity couplant to cling to the desired test location.
When performing shear wave testing, a high viscosity couplant is needed to couple shear waves since gel or liquid couplants do not support shear stress.
Magnaflux products have varying viscosities to fit each application. Ultragel II is a medium viscosity gel (80,000 cP) and is good for general purpose applications, while Sono 600 is a much higher viscosity gel (500,000 cP). For reference, our Ultrasonic Couplant Comparison chart shows viscosities of all products.
Dry time
Couplants will not function properly in transmitting energy once they are dry. Slower drying couplants reduce material usage, speed up processing, and are critical for longer term testing such as long-term flow metering.
Ultragel II has humectants to slow the dry time and avoid issues of dry out or signal dropout. Oil-based couplants, such as Sono 600, provide a similarly consistent signal transmission throughout the inspection.
Part Size
If the part or test area is relatively large, it is important to use a couplant that is self-leveling to minimize the amount of time spent applying the couplant.
Conclusion
Magnaflux couplants are formulated and approved for use in NDT applications, with multiple options available to fit different conditions.