Evaluating the condition of a collection of similar elongated hollow objects

A method of evaluating the condition of an elongated hollow object from a plurality of similar objects existing as part of a bundle of these objects, for example pipes or tubes found in heat exchangers and reactors. The response of each object to a probe of a non-destructive testing system at a plurality of points along the length of the object is recorded and the results are statistically analysed for each measurement point in comparison with the respective measurement point for a particular object. This is used to define an adjusted result for that measurement point for that particular object. The probe may be an acoustic pulse reflectometry probe and the method may be used to identify the location and size of flaws, wall loss and blockages or obstructions in pipe bundles. The statistical analysis may produce an ensemble mean to be used as a baseline for comparing the individual measurement points.