Novel instrumentation to detect sliding and erratic bed load motion

Abstract

Instrumentation was developed to detect the onset of sliding and stationary bed conditions for settling slurries by using non-invasive, external sensing heads. These heads were configured in such a way that suitable data could be obtained and processed online. Tests were conducted at different test facilities with metallic pipes providing internal diameters ranging from 40 to 150 mm, and with various pipe wall thicknesses between 2 and 18 mm. While the clamp-on sensors were able to detect stationary beds on thick-walled pipes within a minute, only the 2 mm-thin spool pieces were able to detect erratic bed motions due to the sensors’ fast response capability. This required additional features to focus the sensing area directly onto the pipe invert. The unique strength of this technique lies in its ability to distinguish between a moving bed, the sudden erratic stick-and-slip motion, and a completely stationary bed right at the pipe invert. Test results ranged in accordance with volumetric concentrations of 11 to 36% and different particle size distributions. It is shown that when the mean velocity was very slowly reduced, the entire spectrum, including the erratic motion, was clearly recognisable from the data pattern. In fact, the pulsing eddies, recorded optically, coincided with distinct signatures in the data. The clamp-on sensors can be deployed rapidly onto any pipe diameter without interrupting the pumping operations. As the thermal sensors do not work on rubber-lined pipelines, a novel industrial design was conceptualised to install such instrumentation between the couplings of lined pipelines. Such short, flange-type inserts can be manufactured from superior-quality steel to provide good wear resistance at the exact internal diameter of the lined pipes, and can be as short as 50 mm.