Heat Exchanger Tubing: Extending the Reach of IRIS Inspections

The internal rotary inspection system (IRIS) is an ultrasonic testing (UT) technique commonly used to inspect a wide range of ferrous and non-ferrous tubing materials in heat exchangers. The technique has proven effective and reliable in detecting and sizing general wall loss and localized corrosion at the inner (ID) and outer (OD) diameters. IRIS is the most popular inspection technique worldwide for its sizing capability. The most common IRIS systems are, however, only suitable for the typical 1.0 in (25.4 mm) and 0.750 in (19.05 mm) tubing and offer a relatively low pulling speed. This paper discusses the evolution of IRIS technology and includes laboratory and field-testing results on typical heat exchanger tubing. A micro-turbine combined with a dedicated centering device equipped with spring-loaded arms offers a unique alternative when inspecting small-diameter tubes—0.500 in (12.7 mm)—at fast pull speeds. This centering device design is highly durable and offers straight C-scan imaging results, which are easier to analyze than conventional IRIS imaging results. At the other end of the spectrum, extra-large centering devices support tube diameters ranging from 3.0 in to 6.6 in (89–167 mm) at reasonable pull speeds. To further extend the applicability of IRIS, a custom, single-part, flexible turbine and centering device enables users to easily manage tube bends and elbows by increasing the bend area inspection zones that can be scanned in a single pass. These new IRIS technology developments have proven challenging, but result in a wider range of applications for IRIS.

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