Galvanizing and re-galvanizing radiators

What is galvanizing?

  • Hot dip galvanizing is the process of coating steel with a thin zinc layer, by passing the steel through a molten bath of zinc at around 460º C.

  • When exposed to the atmosphere, the pure zinc forms zinc carbonate, a strong material that protects the steel beneath from the elements.

  • The zinc will prevent corrosion of the protected steel by forming a physical barrier and self-sacrificing if this barrier is damaged.

  • The life of the galvanized coating depends on the environment and the original coating thickness.

  • Coating thickness depends on steel thickness. A heavy coating will be deposited on a thick steel plate, whilst a relatively thin coat is applied to 22 gauge panel steel (which is typically used in radiator construction).

  • Properly applied galvanized coatings protect radiators from corrosion in many situations.

  • In situations of light to medium transformer service, galvanizing alone can afford long term protection to the radiators.

Example of a galvanized radiator (fin structure in evidence)

The re-galvanization process

Radiators that have never been galvanized or on which the galvanizing has deteriorated, can be galvanized again, but be aware that this can be an expensive and complex process:

  • First the radiator interior is de-greased, water-flushed and hot-air dried. This is a critical step as the galvanizing medium is heated to 460ºC and any paint or oil left inside the radiator would either carbonize or explode.

  • Any existing coatings and corrosion are then acid pickled so that the radiator is stripped back to a clean substrate. The molten zinc required for galvanization will not coat over the top of old galvanizing or paint.

  • Steel drain plugs and flange plates are gasketted with heat resistant material to ensure full coating of the galvanizing and to prevent bonding of the steel to the radiator via the galvanizing medium.

  • The radiator is then dipped in a galvanizing bath of 460ºC molten zinc.

  • A hot oil re-flush at 65C for 2 hours is then undertaken to clean the radiator.

  • Finally, pressure testing is done at 2 bar for 1 hour to reveal any weaknesses.

  • Not all radiators are suited for this process, particularly if age and corrosion have taken their toll.

  • Molten zinc is extremely dense and very large weights need to be applied to force the units into the bath. This creates stress on the structure and any weak points could collapse under the pressure.

  • Once galvanized (or re-galvanized) the radiators can be painted (our recommendation) or erected as galvanized units only. The same process can be applied to transformer pipework, frames and tanks (examples below). 

 

Galvanized pipework

Painting Galvanized Steel

Why paint galvanized steel?

For additional protection against the elements.

  • Applying a good quality paint system over the original galvanized coating is known as a ‘duplex-galvanizing-plus-painting system’.

  • Duplex coatings have been proven to last up to three times as long as the combined life of a paint coating and galvanizing alone (from testing undertaken by The Australian Galvanizers' Institute).

  • Duplex coatings have been proven to be very cost effective in areas where conditions are harsh and access is difficult (tests performed for the Institute by the Stichting Doelmatig Weathering Station in Amsterdam).

  • A further consideration is that the general public expects utilities to be uniform, aesthetically pleasing, environmentally responsible and discreet in appearance.

When is it cost effective to paint galvanized steel?

  • When a radiator or transformer is in heavy service.

  • When the transformer is exposed to harsh environments such as salt air, air pollution and the sulphur rich atmosphere of the central North Island.

  • When access to the transformer is difficult, and freedom from maintenance is a priority.

  • Or solely for aesthetic purposes.
Examples of painted galvanized radiators

 
If there is any doubt about the galvanized-only radiator, we would recommend a paint system be applied over the galvanizing to provide near-ultimate protection of the underlying steel.

The Final Product >