Cold bonding vs welding: the cold bonding process, its limits, and when welding still wins

Cold bonding vs welding comes down to heat. Cold bonding repairs or rebuilds metal with polymer compounds — typically metal- or ceramic-filled epoxies — that cure at ambient temperature, with no hot work and no heat-affected zone. Welding fuses metal and restores metallurgical continuity, but requires hot-work controls, a qualified procedure and, most of the time, a shutdown.

Neither method replaces the other. The useful question is which one fits the defect, the base metal, the service conditions and the outage window.

What is cold bonding?

Cold bonding is a repair method in which a polymer compound — most often a two-component epoxy loaded with metal (steel, aluminium) or ceramic particles — is applied to a prepared metal surface and cures by chemical reaction at ambient temperature. No arc, no flame, no preheat: the base metal is never heated.

On industrial sites, cold bonding covers three families of work:

• Rebuilding: restoring wall loss from corrosion, erosion or cavitation.
• Sealing and reinforcing: closing pits, cracks or small leaks, alone or combined with a fibre-reinforced composite wrap on piping and tanks.
• Bonding: fixing brackets, wear liners or patch plates with structural adhesives instead of welding.

Some catalogues sell these filled epoxies as "cold weld" compounds. That is commercial shorthand: the repair is adhesive, not a weld.

Cold bonding is not cold welding (or weld bonding)

Cold welding — cold pressure welding, process 48 in ISO 4063 — is a solid-state metallurgical process. Two clean metal surfaces are pressed together hard enough for their atoms to bond, without melting and without any adhesive. It is a manufacturing process (butt-joining aluminium or copper wire, for example), not a field repair method.

Weld bonding is a hybrid assembly method used in sheet-metal fabrication, notably vehicle bodies: resistance spot welds are made through a layer of structural adhesive, so the joint combines both mechanisms.

The cold bonding process, step by step

A cold bonding repair is only as good as its surface preparation and its cure. The sequence below is standard practice; exact values — anchor profile, pot life, recoat window, cure time — come from the product data sheet.

1. Assessment. Characterize the defect (wall loss, pitting, erosion, crack, leak) and the service: fluid, pressure, temperature, cyclic or impact loads. Confirm the base metal and remaining wall. This is where cold bonding, composite repair or welding is chosen.
2. Degreasing. Solvent-clean oil and grease first (SSPC-SP 1); blasting over contamination drives it into the surface.
3. Surface preparation. Abrasive blast to a near-white finish — ISO 8501-1 Sa 2½, equivalent to SSPC-SP 10 / NACE No. 2 — or, where blasting is not possible, power-tool clean to bare metal (SSPC-SP 11). Produce the angular anchor profile the manufacturer specifies, assessed per ISO 8503. For immersion or salt-exposed service, check soluble salts (ISO 8502-6 and -9) and dust (ISO 8502-3).
4. Conditions check. Keep the surface at least 3 °C above the dew point, and substrate and ambient temperatures within the product's application range. Condensation destroys adhesion; cold steel slows the cure.
5. Application. Mix at the stated ratio, apply within the pot life, and work a first thin layer into the profile to wet the surface fully before building thickness. Rebuild to shape with templates or moulds.
6. Reinforcement, where needed. Bridging a hole may call for a bonded metal patch or mesh. Pressure-retaining repairs on piping or vessels use a fibre-reinforced composite system designed to a recognized standard (see below).
7. Cure. Allow the cure stated on the data sheet for the actual temperature before returning to service. Where the manufacturer allows accelerated cure, it uses controlled warm air or heating blankets — never an open flame.
8. Inspection. Visual check for voids, runs and edge disbondment; hardness check against the data sheet value to confirm cure; dimensional check on rebuilt surfaces; holiday testing where the repair doubles as a lining.

Once cured, most metal-filled compounds can be machined, drilled and tapped back to dimension.

Cold bonding vs welding: detailed comparison table

What drives the cost difference between bonding and welding

No single figure holds across sites. What is predictable is where the money goes. A weld repair on process equipment carries cost items well beyond the weld itself:

• the hot-work permit, gas testing and fire watch for the duration of the work;
• draining, cleaning, gas-freeing or inerting of the equipment;
• a qualified welding procedure (WPS/PQR) and welders qualified for the base metal;
• preheat and, where the code requires it, post-weld heat treatment;
• non-destructive examination — radiography, ultrasonic, magnetic particle or liquid penetrant, as specified;
• a hydrostatic or pneumatic test after repair where the code calls for it;
• and downtime, from isolation to return to service, which on production equipment usually outweighs everything else.

A cold bonding repair removes most of those items. Its cost sits in surface preparation, material, application labour, cure time and inspection. Compare total cost including lost production, never material cost alone.

When cold bonding is the right choice

• ATEX zones, hazardous locations and fire-risk areas. A cold repair removes the ignition source that would otherwise mean shutting down and gas-freeing a unit. Surface preparation must still suit the zone: grinding and some blasting methods produce sparks, and many sites control them under their own permit. See our guide to repairs in ATEX zones without hot work.
• Cast iron and hard-to-weld metals. Cast-iron pump casings, valve bodies and gearbox housings are prone to cracking under the welding thermal cycle; cold bonding avoids that cycle entirely.
• Parts repaired in place or in service. Large casings, tank walls and embedded components that cannot be dismantled.
• Erosion-corrosion and cavitation. Ceramic-filled compounds rebuild and protect surfaces worn by abrasive or turbulent flow — a frequent case on centrifugal pump casings and impellers.
• Rebuilding worn surfaces. Shafts, bearing seats, keyways and corroded flange faces repaired without machining.
• Short outages. When the repair has to fit inside a planned window or an unplanned stop.

When welding is required

• Primary structural repairs. Load-bearing members, replacement of pressure boundary, cracks that propagate under load — anywhere the design assumes metallurgical continuity.
• Stresses or temperatures beyond the polymer. Service temperature above the product's rated limit, high peel, cleavage or impact loads, severe thermal cycling.
• Code requirements with no alternative. Where the governing code, the insurer or the jurisdictional authority requires a welded repair and does not accept a nonmetallic one on that equipment.
• Defects outside the qualified envelope. When the damage exceeds what the composite or bonding system has been qualified for.

Standards: ASME PCC-2 and ISO 24817

Cold bonding in the broad sense is not governed by one code. For pressure-retaining repairs, the reference is ASME PCC-2, Repair of Pressure Equipment and Piping. Its Article 4.1 (numbered 401 in recent editions) covers nonmetallic composite repair systems for high-risk applications on piping and pressure equipment, including tanks and vessels; Article 4.2 covers lower-risk applications. ISO 24817 covers composite repairs for pipework on closely aligned principles. Both require qualified material data, a defined design life, trained installers and documented inspection — but neither makes a repair acceptable on its own: the governing in-service code (API 510, API 570, API 653), the owner, the inspector and the jurisdiction decide. The detail is in our article on what ASME PCC-2 authorizes; for atmospheric storage tanks, see API 653 and composite tank repairs.

Typical cold bonding applications

FAQ

What is the cold bonding process? Assessment, degreasing, blasting to Sa 2½ (or power-tool cleaning to bare metal) with the specified profile, dew point check, application within pot life, reinforcement where needed, cure per the data sheet, inspection.

Is cold bonding as strong as welding? Not in the same way. A qualified weld can match the base metal; an adhesive repair performs best in shear and compression. For rebuilding, sealing and wear protection that is sufficient; for primary structural load paths, welding remains the reference.

What's the typical cost difference between bonding and welding? It depends on the equipment and the outage. The difference comes from the items welding adds — hot-work permit and fire watch, gas-freeing or inerting, qualified procedure, heat treatment, NDE, pressure testing — and above all from downtime. Compare total cost including lost production.

Is a "cold weld" the same as cold bonding? When the term describes an epoxy repair compound, yes — it is a trade name for cold bonding. In metallurgy, cold welding (cold pressure welding) is a different, solid-state process used in manufacturing, not in field repair.

Can cold bonding be done on equipment in service? Sometimes. External repairs on live piping and tanks are possible with qualified systems, after a safety and engineering assessment. Sealing an active leak requires a system specifically qualified for through-wall defects.

How long does a cold bonding repair last? It depends on the product, surface preparation, service conditions and design basis. Engineered composite repairs have a defined design life under ASME PCC-2 or ISO 24817; every repair belongs on the inspection plan.

In practice

Induscoat performs cold bonding repairs on pumps, exchangers, flanges, tanks and piping in Quebec and Ontario through its maintenance and rehabilitation service, from surface preparation to cure verification. See our cold bonding repair page, and send us the inspection findings, the base metal and the service conditions to request a quote; when welding is the right answer for your defect, we will tell you. Technical data sheets for the Induscoat range are published on the brand site, induscoat.com.