IRIS (internal rotating inspection system) is a technique that can be applied to both ferrous and non-ferrous materials and even non-conductive materials like plastics. With IRIS, the remaining wall thickness of tubes can be accurately measured. IRIS inspection is more accurate than other tube-inspection techniques and has the advantage of presenting information about the geometry of defects. Local defects and wall loss on both sides of the tube can be accurately measured. Defects under support plates can be measured without any limitations. The probe used in IRIS examination is made up of a centering device, an ultrasound transducer and a rotating mirror. An ultrasound pulse is generated in the transducer that is mounted in an axial direction, then a 45-degree rotating mirror in the probe will guide the sound bundle towards the tube wall. Next, there will be an ultrasound reflection (echo) at the inner and outer walls of the tube. These echoes are reflected back and processed by the equipment. The time between these two echoes represents the wall thickness of the tube. Knowing the sound velocity in the material under test enables the wall thickness to be calculated. Water is used to rotate the probe mirror and is also needed as a couplant between the transducer and the tube wall. A calibration standard of the same material and dimensions as the tubes to be examined is used to check the IRIS system response in preparation for the inspection. The tubes should also be cleaned to an acceptable standard.