HVAC Industry

Galvanic corrosion at the carbon-steel-to-copper-tube interface is the dominant failure mode on shell-and-tube chiller water boxes, and the alternative to in-situ rebuild is replacing the entire water box assembly — a long-lead-time, capital-equipment-grade scope item. The Belzona repair sequence is to mechanically prepare the corroded substrate, rebuild the metal loss with Belzona 1111 (Super Metal) or 1121 (Super XL-Metal) for heavier sections, and top-coat with Belzona 1321 (Ceramic S-Metal) for the erosion-resistant face in continuous immersion to 60°C/140°F. The KHIA case Belzona Protects Chiller Tube Sheet documents the procedure on an operating chiller; the same logic applies across centrifugal, screw, and absorption chiller types.

Tube-to-tubesheet seal leaks are repaired with the 1311 (Ceramic R-Metal) family rather than re-rolling, which on aged tube bundles risks further damage. The face of the tube sheet is rebuilt with 1311; the interface seal is restored without disturbing the existing tubes. Cold cure preserves the OEM tube material specification.

Cooling tower water-handling assets corrode from the inside under continuous wet service, and the wet/dry interface drives the most aggressive corrosion. Belzona 5811 (Immersion Grade) coats the basin internals and distribution piping. Cooling tower fan blades that have lost their leading-edge profile are rebuilt with the 1000-series composites and finished with Belzona 1341 (Supermetalglide); the same erosion-resistance face used on similar applications in power generation.

AHU corrosion is driven by condensation cycling on cooled surfaces, and the failure typically appears first at coil headers, casing seams, and condensate pan welds. Belzona 5811 (Immersion Grade) applies to the internal casing and condensate pan; coil header repair uses the 1000-series rebuild stack. Belzona 5831 (ST-Barrier) is specified where the substrate cannot be fully dried before coating — a common condition during in-occupied-building maintenance windows.

Ductwork joints fail under thermal cycling, vibration, and accumulated condensate at low points. Belzona 2211 (MP Hi-Build Elastomer) is the movement-tolerant joint and seam restoration material — the elastomer accommodates thermal expansion without cracking. For internal corrosion in steel ductwork (more common in industrial than commercial HVAC), the same 5811 immersion-grade coating used on cooling tower internals applies.

HVAC does not carry the same hard regulatory approval framework as potable water or food contact service. The relevant standards are AHRI performance ratings (which apply to the equipment as supplied, not to repair coatings), ASHRAE recommendations (advisory), and OEM warranty terms (which cold-cure repair generally preserves where welding would void). For potable water in HVAC service — humidifier feed, drinking water in coils, or steam humidification — the NSF/ANSI 61 stack from the water and wastewater portfolio applies. Confirm the contact mode and the operating temperature against the specific Belzona product number before specification.

Adjacent sectors with shared asset types: Data Centers Industry (CRAC and chilled water overlap), General Maintenance, Healthcare Industry (in-occupied-building HVAC overlap). Asset-level deep dives: Heat Exchangers, Heat Exchangers Tube Sheets, Fans, Blowers & Compressors, Pipelines, Valves, Pipes & Fittings.