How to Protect Tower Internals During Vessel Abrasive Blasting and Recoating

Abrasive blasting and recoating a tower shell can restore the vessel’s corrosion protection while silently damaging the internals inside it. Blast media can plug distributor holes, abrade thin mesh, enter packing beds, contaminate stainless surfaces, and jam moving tray valves. Coating overspray can reduce hydraulic openings, bond removable parts together, cover electrical bonds, and obstruct drainage.

The work boundary must therefore extend beyond the shell surface being repaired. The owner should decide which internals will be removed, which can remain, how retained equipment will be isolated, and how cleanliness and functionality will be verified before closure.

Determine Whether Removal or Protection Is Safer

Removing internals avoids direct blast and overspray exposure but introduces handling, storage, identification, and reinstallation risks. Large or fragile assemblies may be more likely to suffer damage during removal than under a well-engineered protective enclosure. Retaining internals reduces schedule but makes hidden contamination difficult to inspect.

The decision should consider internal type, material, condition, accessibility, packing-bed depth, blast method, abrasive, coating system, ventilation pattern, and required shell area. Wire mesh, fine distributors, plastic components, ceramic packing, and moving valves are particularly difficult to protect and clean after contamination.

Do not assume that a plastic sheet placed over an opening provides adequate isolation. Abrasive ricochets, high air velocity, sharp edges, worker movement, and coating solvents can tear or dislodge temporary barriers. Blast dust travels through small gaps and ventilation currents.

Understand the Damage Mechanisms

Direct abrasive impact removes metal and rounds sharp hydraulic features. Thin wires can break; perforation edges can enlarge; coating on retained internals can be stripped. Ricochet can damage components outside the operator’s direct line of sight.

Deposited abrasive adds weight and blocks flow. Media entering distributor laterals may remain hidden until startup. Particles lodged in packing increase pressure drop or create local liquid maldistribution. Abrasive between sliding tray valves and guides can prevent movement.

Contamination depends on media composition. Carbon-steel shot or recycled abrasive can embed iron in stainless surfaces. Chloride-contaminated media or water can initiate localized corrosion. Silica, fibers, coating flakes, and soluble salts may contaminate the process or downstream catalyst.

Overspray changes dimensions. Small holes, slots, mesh openings, bolt threads, expansion gaps, and drain paths are vulnerable. Coating on gasket faces or panel overlaps can prevent sealing; coating across a removable seam can make later disassembly destructive.

Create an Isolation and Protection Plan

Mark the blast zone, retained-internal zone, ventilation direction, access path, waste-collection area, and pressure boundary of each enclosure. Barriers should be compatible with the abrasive, coating solvent, cure temperature, and expected airflow. Their supports must not overload or damage internals.

Use rigid covers where a flexible sheet could be drawn into a distributor or torn by ricochet. Seal edges without applying unapproved adhesive to process-contact surfaces. Provide witness tabs or pressure indicators where necessary to confirm that enclosure integrity was maintained.

Protect drain openings, but do not create a trapped-liquid or trapped-pressure hazard. Temporary plugs and covers need unique identification and an accountable removal register. Every barrier component must be recoverable before closure.

Separate blasting hoses, scaffold standards, lighting, and extraction ducts from vulnerable internals. Hoses dragged over tray edges can deform panels even if blasting never reaches them. Extraction flow should capture dust without pulling temporary covers into openings or distributing contaminants through the packing.

Coordinate Surface Preparation and Coating Application

Inspect the shell and adjacent attachments before work begins. Define termination points around support rings, clips, welds, linings, and existing internal coatings. Blasting close to an attachment can undercut its coating or damage a corrosion-resistant overlay.

Confirm abrasive cleanliness, size, hardness, recyclability, and soluble-contaminant limits. Recycled media should be controlled for oil, salts, metal fragments, and previous coating debris. Compressed air must be dry and oil-free to the project requirement.

Coating application should include overspray control, ventilation, lighting, and cure monitoring. Masking dimensions must account for final coating thickness and removal technique. Removing masking before adequate cure can pull coating from the edge; removing it too late can tear the film and leave a discontinuity.

Where internals include intentional electrical bonds, coated contact points can destroy continuity. These points should be identified before work and tested after reinstatement. Likewise, fireproof, oxygen-clean, high-purity, or lined equipment may require more stringent contamination controls than ordinary vessel coating work.

Cleaning and Inspection Before Reassembly

After blasting, remove abrasive using methods that do not drive it deeper into laterals, mesh, joints, or packing. Vacuum extraction is generally more controllable than indiscriminate compressed-air blowing, but suction tools must not seal against and collapse thin components.

Inspect hidden horizontal surfaces, tray undersides, trough ends, downcomers, gas risers, mesh layers, packing supports, and shell-ring crevices. Use borescopes or opening of accessible covers where needed. Count and remove every temporary plug, sheet, rigid cover, fastener, and support.

After coating cure, inspect for overspray, blocked holes, bonded moving parts, covered identification, damaged gaskets, and coating bridges across expansion joints. Verify distributor openings, tray valves, drains, vents, manways, and sliding details mechanically. Water testing may be appropriate for coated distributors.

Stainless internals exposed to iron-bearing media may require contamination assessment and approved restoration. Do not perform unplanned acid cleaning inside a newly coated vessel; cleaning chemistry can attack or stain the fresh coating.

Documentation and Release

The work package should record retained and removed internals, their condition, protective barriers, abrasive batch, air-quality checks, coating batch, environmental conditions, inspections, cleaning results, repairs, and temporary-item reconciliation. Photographs should cover critical hidden zones before they are closed.

Final release requires separate acceptance of the shell coating and the tower internals. A coating holiday test proves little about a blocked distributor hole or contaminated packing bed. Operations, inspection, coating, and internal specialists should confirm that both corrosion protection and hydraulic function have been restored.

Successful recoating leaves the shell protected without making the internals the waste collector for the maintenance project.