Non-invasive inspection of heat exchanger tubes

Two well-known methods for inspection of tubes and pipes are Acoustic Pulse Reflectometry (APR) and Guided Waves (GW). Both are based on probing the tubes/pipes using long range acoustic waves, either through the air in the tubes (APR) or the tube walls (GW). Both methods share the advantage of being non-traversing, enabling very short inspection times, on the order of 10 seconds per tube. In addition, each method has complementary advantages and disadvantages. APR for example can detect blockages and very small pinholes but is insensitive to Outer Diameter (OD) defects. GW, on the other hand, can detect OD faults but cannot easily distinguish pitting from through-holes. As opposed to APR, which has been applied to tube inspection for several years, GW has been used mainly for screening applications in large diameter pipes. In this paper we first present several recent developments in GW, giving an implementation that can fit into tubes as small as 3/4″ and capable of detecting, classification and sizing of defects. We term this implementation Ultrasonic Pulse Reflectometry (UPR). We then show how a combined system containing both APR and UPR in a single probe provides a comprehensive solution to tube inspection, enabling very rapid inspection and capable of detecting all typical tube defects.