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Introduction to Internal Rotary Inspection System- IRIS


1. The principles of Internal Rotary Inspection System (IRIS):

Internal Rotary Inspection System is an ultrasonic technique, it requires a couplant. In this case, water. Tubes under test must therefore first be flooded to use this technique. IRIS relies on a transducer to generate an ultrasonic pulse parallel to the axis of the tube under test. It also relies on a rotating mirror that directs the ultrasonic wave into the tube wall. The mirror is driven by a small turbine powered by the pressure of water pumped into the tube.
Part of the ultrasonic wave is reflected by the inner-diameter (ID) wall, while the rest is reflected by the outer-diameter (OD) wall of the tube. Because the ultrasonic velocity of the tube’s material is known, it is possible to assess the thickness of the wall by calculating the difference in times of flight between the two diameters.

Picture 1: Internal Rotary Inspection System (IRIS).

2. The process of Internal Rotary Inspection System (IRIS):

- A transducer located inside a turbine generates an ultrasound pulse along the axis of the tube.

- The ultrasound is reflected on a 45o mirror and oriented toward the tube wall thickness.

- The ultrasound is partially reflected on the ID, then transmitted inside the wall, and finally reflected on the OD.

- Knowing the ultrasound velocity in the tube material, the wall thickness can be calculated by using the time of flight difference between the OD and ID echoes.

- A water flow is going inside the cable and then the turbine.

- The mirror, attached to the rotor part of the turbine, rotates continuously at the speed at about 50 rev/s.

- This rotation allow a full inspection of the tube wall thickness.

- A small pin attached to the turbine body produces an ultrasound reflection each time the mirror passes under it.

- The reflection from the pin is used to synchronize the screen display.

Picture 2: The process of Internal Rotary Inspection System (IRIS).

3. Advantages and Disadvantages of Long range ultrasonic Testing

- Advantages:

  • Suitability for ferrous and non-ferrous materials
  • Detection of corrosion, pitting and wall loss
  • Accurate wall thickness measurements
  • Sensitivity to both internal and external defects
  • Defect position can be located in relation to tube length
  • 100% coverage of the tube
  • Results data storage
  • Flexibility as a back-up to remote field, magnetic flux leakage and eddy current inspections

- Disadvantages:

  • Require plenty of  time to repair and calibrate the equipment.
  • This technique cannot detect cracking.
  • Internal cleaning must allow access to heavy scale and debris free surfaces.
  • Compared to techniques such as eddy current; the scan speed is slower. The pulling speed; 2 in/s.

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