This line was the feed to a reactor vessel in a chemical plant and was normally insulated. It emerged from the reactor 2m above ground level, ran vertically for 7m, then horizontally for a further 10m. Visual inspection was difficult owing to the insulation and access was not feasible to the elevated section without scaffolding. External corrosion under insulation (CUI) was suspected. The Teletest ® transducer was attached near the base of the vertical section, with the aim of examining the vertical and elevated horizontal legs. An example of the Teletest ® A-Scan output is shown below. The two lines are distance amplitude correction (DAC) curves, the upper being the amplitude from butt welds in the pipe and the lower the reporting level. The large peak 5m from the transducer is a weld at the elbow where the pipe turned to the horizontal. A number of flaws were reported from 13 to 19m from the transducer (marked '+' on the plot).
On removal of the insulation for cleaning and visual inspection, these were confirmed as areas of CUI attack. Some of these are shown below.