Lack of Signals in IRIS Inspection Due to Rough-Surfaced Tubes

Lack of Signals in IRIS Inspection Due to Rough-Surfaced Tubes

#IRIS #tubeinspection #tubecleaning #surfacepreparation #Internal Rotating Inspection System #Hext exchanger tube #Tube cleaning and surface preparation #Inspection technique limitation

AUTHOR: Chokanan Kittheera-anan / Puripong Klamdith

Key Learning Point:

“Centering the IRIS probe and adjusting the software parameter setup are essential for improving signal quality in tubes with rough internal surfaces.”

 

Background:

 

            The tube inspection operator performed an inspection inside the heat exchanger tubes made of Carbon Steel SA-179, with dimensions of OD 19.00 x 2.10 mm, using the Internal Rotating Inspection System (IRIS). During the first inspection, the minimum wall thickness recorded was 1.75 mm, as indicated by the signals in Figure 1, where some signals were found to be missing. The operator then utilized a borescope and observed that the internal surface of the tube was rough and uneven throughout (as shown in Figure 3), revealing defects characterized as internal wall loss. This condition caused the probe used for inspection to wobble while collecting signals, making it impossible for the sound waves to maintain a perpendicular angle to the tube surface, resulting in signal loss (the internal roughness affected the signal reception). An example showing the transmission and reception of sound waves is illustrated in Figure 4, leading to inaccuracies in the assessment.

Consequently, the operator modified the probe to reduce wobble (changing the centering device of the probe) and adjusted the parameters of the software setup used for the inspection to enhance the signal resolution. Upon re-inspection, the signals received were clearer, and the minimum wall thickness was recorded at 1.38 mm, as indicated by the signals in Figure 2.

Figure 1: Signal image from the internal inspection of the tube using the IRIS method from the first inspection.

Figure 2: Signal image from the internal inspection of the tube using the IRIS method from the second inspection.

Figure 3: Image of the rough surface inside the tube from the borescope.

Figure 4: An example illustrating the transmission and reception of sound waves.

Technical Detail:

 

       The Internal Rotating Inspection System (IRIS) is an inspection technique that relies on ultrasonic principles, providing high-resolution inspections capable of accurately measuring remaining wall thickness. However, for ultrasonic techniques to be effective, the surface being inspected must be relatively smooth and clean. In the case discussed in this lesson learned, the internal surface of the inspected tube was characterized by roughness distributed throughout, which prevented the sound waves from achieving a perpendicular angle to the tube surface and resulted in the inability to receive reflected signals for processing (the roughness inside the tube contributed to signal loss).

 

          To mitigate the wobble of the probe used in the inspection due to the internal roughness of the tube, it was necessary to adjust the probe to ensure it was centered as much as possible. This adjustment allows the sound waves to reflect perpendicularly off the tube surface, facilitating the reception of clear return signals. Additionally, the parameters in the software setup needed to be appropriately adjusted by increasing the gain for both the Front wall echo and Back wall echo to compensate for signal attenuation caused by the refraction of sound waves from the rough inner surface of the tube.

Lesson learned:

 

“Inspecting tubes with rough internal surfaces using IRIS requires the probe to be centrally adjusted and the software setup parameters to be appropriately configured.”

 

          In cases where tubes with rough internal surfaces are inspected using the Internal Rotating Inspection System (IRIS), the signals obtained may be unclear due to the roughness inside the tube. This condition can cause the probe used for inspection to wobble, resulting in a lack of accurate information and potentially leading to erroneous assessments.

 

          To prevent encountering unclear signals, it is essential to adjust the probe to ensure it is positioned as centrally as possible. This adjustment allows the sound waves to reflect perpendicularly off the tube surface, facilitating clear return signal reception. Additionally, the parameters in the software setup should be adjusted appropriately by increasing the Gain for both the Front wall echo and Back wall echo to compensate for signal attenuation caused by the refraction of sound waves from the rough inner surface of the tube.

 

          The inspection process should follow the steps outlined in the flowchart shown in Figure 5 to achieve the specified C-Scan Quality signal.

Figure 5: Flow chart illustrating the procedure for inspecting the internal of tubes using the IRIS method.

Figure 6 : Note 1 C-scan quality level