Conveying solid particle products through rigid pipe systems is an inherently noisy process as the particles hit the undamped metal pipe walls.
Few available materials exist that can cushion the impacts by incorporating internal 'soft' linings. Many need to withstand the effects of long-term abrasion; others have to meet strict hygiene requirements. There are also engineering difficulties when fixing linings to often intricate runs of small diameter piping.
One flour mill reduced noise levels by applying acoustic lagging to the external surface of the pipe run. It was also necessary to ensure rapid access to a number of inspection panels built into the pipe runs and for the lagging to be removable for pipe cleaning.
Soft thermal-type lagging was discounted on mechanical grounds and because it was difficult to handle. Instead the lagging was pre-fabricated in a series of split semi-circular sections. Each section consisted of a half cylinder of plain sheet steel lined with 50 mm thick semi-rigid mineral wool slab, retained in the half cylinder by perforated sheet steel. The inner diameter of the section was equal to the outer diameter of the conveying pipe concerned.
Two matching sections were placed on opposite sides of the pipe and held in place by over-centre, quick-release toggle clamps. In some cases it was acoustically acceptable to leave one access door in the pipe unlagged. However, where a door was radiating significant noise, the internal perforated sheet and mineral wool infill were omitted from the lagging section and a corresponding hinged access door was provided in the external lagging shell.
About £150 per metre lagged. (1995)
A noise reduction of about 10 to 15 dB. This system of pipe lagging was found to be easily adapted to even complex pipe runs including bends and junctions.
Information supplied by Ian Sharland Limited.