NDTnet 1998 Aug, Vol.3 No.8

Abstract

Internal Rotary Inspection System (IRIS) is a relatively new ultrasonic system used generally for inspection of heat exchanger and steam generator tubes and pipe lines for measurement of wall thinning and pitting due to corrosion. The system has the capability to indicate the reduction in wall thickness taking place either in an outer diameter or inner diameter or from both sides. It also reveals both uniform corrosion and localised pitting corrosion. The equipment has the capability of inspecting tubes of 12 to 70-mm internal diameter. The sensitivity achievable for reliable assessment of corrosion loss by IRIS is of the order of 50µm.

In IRIS, the ultrasonic transducer is supported on a probe carrier and it is centered in the tube. The ultrasonic pulses are emitted along a path parallel to the tube axis. These pulses are reflected by a 45° mirror, mounted on a water driven turbine which makes the point of impingement of successive ultrasonic pulses along the circumference of the tube wall. This arrangement enables to cover the whole circumference of the tube wall with each revolution of the mirror. All the wall thickness measurements made during a scan around the circumference of the tube are displayed on an oscilloscope screen. The image produced is a stationary rectilinear picture of the circumferential cross section (B scan) of the tube.

After calibrating the IRIS equipment with calibration tubes, studies were conducted on tubes of various materials and thicknesses having artificial defects and on the tubes used in process industries having internal and external corrosion associated with severe pitting. A very clear B-Scan display could be obtained from perspex tubes having varying wall thickness and on carbon steel, brass and stainless steel tubes having artificial OD notches and flat bottom holes. Dimensional measurements of the above defects could be correlated with IRIS results. Experiments were also conducted on some of the tubes used in process industries with encouraging results for detection of wall thinning and pitting attack.

Studies were also conducted on tubes having baffle plates and finned tubes. This paper discusses the use of IRIS as an alternate method to multi frequency eddy current testing in overcoming the interference of baffle plates on defect detection. The overall capabilities of the inspection by IRIS, would help in scheduling the periodicity of inspection and life prediction and extension of tubes used in steam generators and heat exchangers.

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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