Repairing a holed chute or hopper without welding

A holed chute or hopper is repaired without welding by closing the opening with a ceramic-filled epoxy composite reinforced with mesh, or by bonding a steel plate or ceramic tiles onto the prepared wall. The repair is done cold, which avoids hot work, and fast-curing products often let the equipment return to service within the same shutdown.

A hole first shows up as a dust or slurry leak, a rust streak on the outside or a pinpoint of daylight seen from inside. Waiting for the next major shutdown to weld in new plate is not always possible, or wise. This guide is for maintenance managers at mines, cement plants, aggregate plants and bulk terminals. It focuses on holes and cold repair; for wear diagnosis and the full range of solutions, including welding, see our guide to chute and hopper wear repair.

Why repair a holed chute without welding?

A chute is repaired without welding because welding on worn plate often creates more problems than it solves: hot work to manage, thinned plate that blows through under the arc, distortion, and neighbouring linings that burn. A cold repair removes these constraints.

• Hot work. Welding requires a hot work permit, a fire watch and often shutting down neighbouring equipment. In combustible dust areas (coal, sulphur, grain, sawdust), the risk is real; prevention rules are set out in NFPA 51B and CSA W117.2, among others.
• Thinned plate. Around a hole, the remaining steel is thin and uneven. It melts or blows through under the arc, and the weld holds poorly.
• Neighbouring linings. Rubber, polyurethane, bonded ceramic and exterior paint degrade under heat.
• Distortion. Heat distorts thin walls and shifts flanges, inspection doors and liners.

Our comparison of cold bonding vs welding details these differences. In a classified area, see also cold repair in ATEX zones.

Which cold repair methods are available?

Three cold repair methods cover most holes: reinforced ceramic-filled composite, bonded steel plate and bonded ceramic tiles. The choice depends on the size of the opening, the condition of the surrounding wall and the wear mode in the zone.

The differences between ceramic and abrasion-resistant steel are covered in our comparison of alumina ceramic vs AR steel. Choosing the composite is explained in our guide to metal repair epoxy putty selection.

How is the wall prepared before repair?

The wall is prepared in four steps: secure the equipment, measure the remaining steel, clean back to sound metal and create a bonding profile. Composite and adhesive only hold on steel that is clean, dry and rough.

1. Lockout and access. Feeders and conveyors locked out, chute emptied, risk of product collapse assessed. The inside of a hopper is often a confined space.
2. Thickness survey. An ultrasonic survey around the hole marks where the steel is too thin. The repair extends to steel of adequate thickness.
3. Cleaning. Removal of stuck product, rust and liner remnants. Abrasive blasting is preferred; where it is not possible, mechanical preparation to SSPC-SP 11 or SP 15, described in our article on power tool cleaning.
4. Profile and edges. Hole edges chamfered, surface roughened over a wide margin around the opening.

One caution: grinding throws sparks. Depending on site procedure, it may itself count as hot work. Preparation methods are agreed with the permit holder before the shutdown.

How does a reinforced composite repair proceed?

A reinforced composite repair works from the outside in: the opening is first closed with a backing, then the composite is built in layers with embedded mesh to the required thickness. The finished surface follows the wall so it does not create a ledge that catches product.

• Backing. A thin sheet, mesh or temporary tape placed on the outside closes the hole and holds the first layer.
• First layer. The composite is pressed into the prepared steel to drive out air and ensure wetting.
• Reinforcement. Metal or fibre mesh is embedded in the composite, lapping well onto sound steel.
• Further layers. The composite is built to the planned thickness, then smoothed in the direction of product flow.
• Wear layer. In a sliding abrasion zone, a ceramic-filled composite layer or bonded tiles finish the repair.

For a bonded plate, structural adhesive is applied to both prepared surfaces, the plate is held under pressure during cure with clamps, props or temporary bolts, and its edges are sealed with composite so product cannot work in underneath.

How can the return to service be accelerated?

Return to service is accelerated with three levers: a fast-curing product, control of wall temperature and preparing the repair before the shutdown. Epoxy cure time depends heavily on temperature; a cold wall lengthens it considerably.

• Product. Fast-setting composites exist for this need. Their cure time before loading is on the data sheet, at the wall temperature.
• Temperature. Heating from the outside or with lamps and enclosures, without exceeding the temperature allowed by the data sheet. Our article on cold weather application covers these precautions.
• Advance preparation. Plates cut and formed, product kits, mesh, backings and heating equipment ready on site.

A prior inspection, done with the plant running where access is safe, lets you measure thin zones and plan quantities. Our maintenance and rehabilitation service organizes these repairs within the available shutdown window.

When is a cold repair not enough?

A cold repair is not enough when the hole affects the load-bearing structure, when the opening is too large relative to the remaining sound steel, when service temperature exceeds the product limits, or when the zone takes large lump impacts that neither composite nor ceramic can absorb.

• Load-bearing structure. Thinned stiffeners, support beams and mounting flanges are replaced or reinforced following a structural check.
• General wear. If the whole wall is thin, a local repair only moves the next hole. Replacing the plate or the box is then more economical.
• Temperature. Near kiln or dryer outlets, the thermal limit of the adhesive and composite is checked.
• Food contact. The products used must suit contact with the conveyed material.

In all these cases, a documented cold repair can remain a stopgap until a planned replacement.

How can the repair be made to last longer?

The repair lasts longer when the cause of the hole is addressed: a misplaced impact zone, a missing liner or a wall angle that slides ore over bare steel. A repair that reproduces the original wall will wear the same way.

Follow-up matters as much as the repair: located photos, thickness readings at the same points and the date of the next inspection. For loadout hoppers, choosing a durable liner is covered in our article on truck loadout chute and hopper liners. Repairs belong within a protective coatings system that also includes exterior corrosion protection, often neglected on chutes.

Frequently asked questions

Can a composite really close a hole in a chute?

Yes, if it is reinforced with mesh, applied to well-prepared sound steel and extended well around the opening. Without reinforcement, it only suits small holes.

Is a hot work permit needed for a composite repair?

Applying the composite or adhesive is cold work. Preparation by grinding, however, may be classed as hot work under the site procedure.

Does the repair hold up under ore?

It holds under sliding abrasion if the wear layer is suitable, for example a ceramic-filled composite or bonded tiles. Under large lump impact, a rubber and ceramic panel is a better fit.

Can the repair be done from outside without entering the hopper?

Partly. A bonded plate on the outside can stop a leak, but wear continues inside. A lasting repair treats the face in contact with the product.

Our crews and qualified subcontractors repair chutes and hoppers on site, working from LaSalle, including in Abitibi-Témiscamingue and on the Côte-Nord. Cold bonding is at the core of this work. Send photos, the hole dimensions, the remaining thickness if known and the shutdown window through the quote request: pricing on consultation, reply within 24 business hours.