Internal Rotary Inspection System
Internal Rotary Inspection System is one of the Non Destructive Testing techniques that is commercially used to inspect pipes and tubes which is acknowledged as crucial for operators in the oil, gas and power generation industries to maintain the integrity of their plant. IRIS method employs an ultrasonic immersion pulse echo technique.
IRIS works by having the probe immersed in a tube flooded with water. The probe is then slowly pulled out while the data is displayed and recorded. An IRIS probe consists of a transducer that generates an ultrasonic pulse and a rotating mirror, driven by a small turbine that is rotated by the pressure of water pumped, to direct the pulse into the tube wall. The entire tube circumference can be fully inspected by the spinning motion of the mirror which results in a helical scan path as it is being pulled out of the tube.
The ultrasonic pulses are reflected from the Inside Diameter (ID) to the Outside Diameter (OD) of the tube. The time interval between the first echo from the internal surface of the tube and the first echo from the outside surface of the tube can be used to calculate the wall’s thickness. Inconsistencies of the thickness can be categorized as results of corrosion, erosion, pitting and wall loss. Therefore, IRIS is commonly used for tube inspection in boilers, heat exchangers, air coolers and feed water heaters.
Among the advantages offered by the IRIS inspection technique are; suitable for ferrous and non-ferrous materials, excellent result in detecting corrosion, pitting and wall loss, accurate wall thickness measurement and full coverage of the tube circumferrence. Despite the advantages, there is still a limitation to the IRIS inspection. The testing requires extensive cleaning of the tube to remove debris, dirt or scales present. This is to ensure smooth turbine movement and also to avoid from missing any defect present at the dirty area.