Specifying and inspecting rubber lining for slurry service: surface preparation, thickness, hardness and spark testing

Equipment

Ash-water and slurry pipework, tanks, mixers, launders and hoppers are protected from abrasion and corrosion by a bonded rubber lining, typically 6 mm of natural or chloroprene rubber, applied to grit-blasted steel with a primer and adhesive system and cured at ambient temperature or with heat.

Failure modes

Wear-through at bends, tees and changes of section where the slurry impinges; disbonding and blistering where the surface was contaminated or the primer window was exceeded; holidays and thin spots that let slurry reach the steel; damage at flange faces during bolting; and mechanical damage in transport and handling.

Common causes

Blast profile too shallow or surface flash-rusted before priming; dust left on the surface; adhesive applied outside its open time; rubber stitched with insufficient overlap; curing in high humidity; and no holiday test before the item went into service.

Inspection and testing

Specify and witness: blast cleaning to ISO 8501-1 Sa 3 with a 40–60 µm profile; dust to ISO 8502-3 rating 1; primer within a stated window after blasting (four hours on the slurry-plant scope); lining thickness measured at defined points, specified thickness ±10%; hardness to ASTM D2240, ±5 Shore A of the specified value; adhesion to ASTM D429 on test plates where required; and holiday spark testing of the whole lined surface to zero defects. Hold and witness points for each of these belong in the quality control plan.

Maintenance

Inspect lined pipework at the wear points on a schedule tied to throughput; rotate spools where wear is one-sided; keep flange bolting to the specified torque so the lining at the face is not crushed; and spark-test suspect items during outages.

Repair

Local damage can be patched by cutting back to sound lining, re-preparing the steel and bonding a patch with overlap, then spark-testing. Where damage is widespread the lining is stripped, the steel re-blasted and the item relined; on the slurry-plant scope, spools damaged in transport were returned to the workshop, relined and re-tested before delivery.

Replacement

Replace the steel item rather than reline it when the wall is thin, when nozzles and flanges are corroded, or when the geometry causes repeated wear at the same point; a redesigned spool with a longer-radius bend often outlasts a relined original.

Umbusso capability

Umbusso fabricated, lined and tested the 250NB and 350NB AWRSE tank outlet pipework and lined the slurry mixers at an Eskom power station as Main Contractor in 2025, to a quality control plan signed by Umbusso QC, the lining subcontractor’s QC, Eskom QC and the Eskom engineer, with a full data book accepted by Eskom.

This article is general technical guidance. Intervals, standards and methods must be confirmed against the current regulation, the manufacturer’s documentation and the site standard before they are applied.