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Internal Rotary Inspection System (IRIS)
IRIS an ultrasonic method of inspection for pipes and tubes, used to provide accurate information, to maximize the efficiency and life expectancy of vital components without sacrificing safety and reliability. Typically used on boilers, air coolers, heat exchangers and feedwater heaters. Due to its high accuracy, IRIS is often used to backup electromagnetic inspections to fine tune the accuracy of data analysis and provide a better understanding of the defects taking place in a specific unit.
As IRIS is an ultrasonic technique it provides greater accuracy in comparison to the electromagnetic techniques and is suitable for ferrous, non-ferrous and non-metallic tubing. The technique detects and sizes wall loss resulting from corrosion, erosion, wear, pitting and baffle cuts in a wide range of tubes and diameters.
Tubes under test must first be flooded (couplant), then an IRIS transducer, used to generate ultrasonic pulses parallel to the wall of the tube under test, is placed inside of a turbine with a rotating mirror set at 45 degrees. The ultrasonic waves generated by the transducer is reflected by the mirror into the wall of the tube. Part of this wave is reflected back from the internal diameter of the tube wall while the remainder of the wave is transmitted through and is reflected back from the outer diameter of the tube wall. The time of flight difference between these two returning waves can be used to calculate the wall thickness. As the IRIS probe is pulled, the spinning motion of the mirror results in a helical scan path ensuring full coverage of the tube. This can be seen in the images below.

Fig 1. Above displays
an ultrasonic pulse generated by the transducer and directed by the mirror.


Fig 2. Above displays
a flooded tube and the rotating mirror.

 

Advantages of IRIS
Accurate wall thickness measurements provided in mm remaining.
Ability to test ferrous, non-ferrous and non-metallic materials
Effectively used to confirm and fine tune electromagnetic methods
Full sensitivity near tube sheets and support plates
Sensitive to internal and external defects
Can display profiles of detected defect mechanisms

Limitations
Slow inspection speeds
Unable to detect through wall defects
Requires clean water as a couplant to flood tubes
Tubes required to be cleaned to bare metal prior to inspection.