Internal Rotary Inspection System (IRIS) is a special type of Ultrasonic Testing technique used for inspection of pipes and tubes. Water is used as a couplant. The tube to be inspected is flooded with water. A transducer generates an electronic pulse parallel to the axis of the tube being tested. A rotating mirror directs the ultrasonic wave into the tube wall. The mirror is powered by a water-driven turbine, with the water being pumped into the tube for flooding.
Parts of the waves are reflected by the ID and OD. Knowing the velocity of ultrasonic waves in the material of the tubes, the wall thickness can be calculated by determining the time required for both waves to be reflected from the corresponding walls. As the probe is pulled, the rotating mirror develops a helical scan path. IRIS can be used for boiler, shell-and-tube and fin-fan heat exchangers.