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Introduction & Basic Principle

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

Primary Advantages

• 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.
• it produces very accurate results (wall thickness measurements typically accurate to within 0.005 inch, or 0.13 mm).
• Works in metal or plastic tubes
• Typical smallest detectable defect: through-hole of diameter 1/16-inch (1.6 mm).

Primary Disadvantages

• The IRIS probe must be moved very slowly (approximately 1 inch per second, or 2.5 cm/s). Hence it is a slow method compare other Heat exchanger examinations like Eddy Current and Remote Field Eddy Current Testing
• 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
• Works for tube diameters of ½ inch (13 mm) and up. Special centralizing devices are needed for larger diameters.
• Can pass bends, but will not detect defects in bends
• Not sensitive to cracks aligned with tube radius.





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