Internal rotary inspection system (IRIS) is an ultrasonic method for the nondestructive testing of pipes and tubes. The IRIS probe is inserted into a tube that is flooded with water, and the probe is pulled out slowly as the data is displayed and recorded. The ultrasonic beam allows detection of metal loss from the inside and outside of the tube wall.
The IRIS probe consists of a rotating mirror that directs the ultrasonic beam into the tube wall. The mirror is driven by a small turbine that is rotated by the pressure of water being pumped in. As the probe is pulled the spinning motion of the mirror results in a helical scan path.
Field-proven and commonly used in boilers, heat exchangers, and fin-fan tubes.
Often used as a back-up to electromagnetic examination of tubes, to verify calibration and accuracy. Especially useful as a follow-up to remote field testing due to the full sensitivity near tube support structures provided by IRIS.
The IRIS probe must be moved very slowly (approximately 1 inch per second, or 2.5 cm/s), but it produces very accurate results (wall thickness measurements typically accurate to within 0.005 inch, or 0.13 mm).
Before the examination, tubes must be cleaned on the inside to bare metal.
A supply of clean water is needed, typically at a pressure of 60 psi, or 0.4 MPa. Dirt or debris in the water may cause the turbine to jam.
Works for tube diameters of ½ inch (13 mm) and up. Special centralizing devices are needed for larger diameters.
Works in metal or plastic tubes
Typical smallest detectable defect: through-hole of diameter 1/16-inch (1.6 mm).
Operates in temperatures above freezing.
Can pass bends, but will not detect defects in bends.
Not sensitive to cracks aligned with tube radius.
IRIS testing world wide. PDF
Tubing Inspection using Multiple NDT Techniques. By Fathi E. Al-Qadeeb. PDF, 118 kB.
Condition Monitoring - Process Plant Tube Inspection: an Ongoing Commitment by Plant Owners and Operators. By Charles Panos. 
NDT and Heat Exchanger Tubes. By Helle H. Rasmussen, Hans Kristensen & Leif Jeppesen.