What causes erosion in pneumatic-conveying bends

When a conveying line changes direction, the gas follows the curved passage while solid particles tend to retain their incoming motion. Their size, shape, density, surface condition and interaction with other particles influence how quickly their path changes. Some strike the outer side of the bend; others rebound, slide or re-enter the stream. Fine and coarse fractions may therefore leave different marks. This qualitative mechanism explains why a bend can be more exposed than a straight run, but it does not identify the dominant cause by itself. The actual particle population and operating state must be observed or measured.

Bend radius, turn angle, cross-section, inlet alignment and whether the bend is horizontal or vertical all influence the local path. A compact turn may concentrate contact, while a broader curve can distribute it differently; neither description guarantees a better result without the duty data. Gravity can shift the solids bed before or through a vertical transition. Reducers, ovality, misalignment and internal ledges can create a local jet or step that overrides the nominal geometry. Record the as-built dimensions and orientation rather than relying only on a drawing. Mark welds, flanges, joints, replaceable backs and access openings on the same damage map.

Gas velocity is relevant, but the wear pattern also reflects solids rate, particle-size distribution, moisture, agglomeration, line pressure and how uniformly material enters the pipe. Startup, shutdown, purging, partial load, plugging and recovery may produce paths that differ from steady operation. A process change can alter several variables at once, so a higher throughput label is not a complete diagnosis. Build a timeline that pairs wear observations with operating modes, alarms, product grades and maintenance events. Where instruments provide averages, check whether short excursions or uneven feeding could be hidden. Preserve uncertainty instead of converting one nominal value into a universal explanation.

A bend may receive an already biased stream. A preceding elbow, tee, valve, feeder, flexible connection, reducer or poorly aligned joint can cluster particles on one side or generate swirl before the inspected component. Internal wear at a flange can form a step that accelerates local damage downstream. Conversely, a downstream restriction may affect pressure and distribution through the bend. Extend the inspection beyond the failed item and document the spacing and orientation of nearby fittings. Compare repeated bends in equivalent service only after confirming that their inlet condition, installation direction and maintenance history are actually comparable.

Before cleaning or removal, photograph the bend with fixed references and mark outer radius, inner radius, sidewalls, inlet, outlet and adjoining straight lengths. Note polished tracks, grooves, thinning, pits, cracks, missing segments, recessed joints, exposed steel and attachment condition. Thickness readings or other inspection methods must follow the component’s approved procedure and site safety controls. A crack at an unsupported edge, corrosion beneath a leak and progressive particle erosion can coexist but require different responses. Retain removed pieces when practical and record their orientation. A labelled map is stronger evidence than a close-up that cannot be located on the component.

Corrective action may combine operating control, feeder adjustment, removal of internal steps, geometry revision, a replaceable wear back or a zoned lining. The solution must preserve the pressure boundary, structural support, internal clearance, grounding or other system requirements identified by the project. Transitions should avoid exposed edges and abrupt ledges, and the attachment method must match temperature, chemistry, pressure condition and installation access. Define inspection points and acceptance criteria before returning the line to service. Review the wear map after representative operation; if the pattern moves, revisit the flow assumptions instead of simply adding material at the previous hotspot.