Internal Rotary Inspection System
IRIS is used to inspect a wide range of materials, including ferrous, nonferrous, and nonmetallic tubing. This technique detects and sizes wall loss resulting from corrosion, erosion, wear, pitting, cracking, and baffle cuts. Typically used to boilers, heat exchanger and fin fan tubes.
Because IRIS is an ultrasonic technique, it requires a couplant. In this case, water. Tubes under test must therefore
first be flooded to use this technique. IRIS relies on a transducer to generate an ultrasonic pulse parallel to the axis
of the tube under test. It also relies on a rotating mirror that directs the ultrasonic wave into the tube wall. The mirror is driven by a small turbine powered by the pressure of water pumped into the tube.
Part of the ultrasonic wave is reflected by the inner-diameter wall, while the rest is reflected by the outer-diameter wall of the tube. Because the ultrasonic velocity of the tube’s material is known, it is possible to assess the thickness of the wall by calculating the difference in times of flight between the two diameters.
As the probe is pulled, the spinning motion of the mirror results in a helical scan pattern and this allows covering all of the tube surface (if pulled at the proper speed).
A critical aspect of IRIS is ensuring that the mirror is at the center of the tube. An off-center ultrasonic pulse yields a distorted scan image because of the different ID and OD wall sound paths. And so IRIS comes with centering devices helping operators keep the system centered in the tube.
Benefits of IRIS
- Works on all materials magnetic or not
- Full sensitivity near tube support structures such as tubesheets
- Perfect as a backup to electromagnetic testing to verify calibration and accuracy
- Very accurate wall thickness measurement results
Ferromagnetic Materials, such as Carbon Steel, can be inspected by IRIS or RFT. IRIS should be used when small pits can be expected. When the damage does not include small pits and is mainly general wall loss, then IRIS or RFT can be used. IRIS will be more accurate but slow and require significant cleaning. RFT will be fast and require minimal cleaning. In case of carbon steel tubes with Aluminum Fins, IRIS should be the preferred technique.