Monitoring of scale progression in a pneumatic conveying system operating in a metal production plant was conducted during a five-month long monitoring period. A combination of an acoustic monitoring method and a laser imaging method provided detailed information of gradual scale growth in a test pipe. The results show that the scale grew steadily throughout the test campaign. Periods of increasing and decreasing scale growth rate as well as episodes where the scale was detached from the pipe surface could be identified. Additionally, visual inspection of images obtained by the laser device offered information about the spatial distribution of the scale in a cross section of the test pipe.