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Suitable Surface Conditions
Large Items or Thick Steels
Adhesive residue contaminates steel surface.
Very thick coatings may form on items which are large
and consist of heavy steel sections. Longer immersion and
handling times required to process these sections may
result in the metallurgical properties of the steel having
high reactivity with the zinc whilst in the galvanizing bath.
Further information relating to zinc reactivity is available in
Effects of Steel Chemistry.
Rusted Items
Light mill scale and surface rust on items can be removed
within our pre-treatment process. Heavily rusted steel will
require abrasive blasting prior to delivery to remove the
rust layers. If the steel surface is pitted after blasting,
this effect will be evident after the hot dip galvanized
coating is applied.
Surface rust is easily removed in our process.
•Cutting Oil
Some cutting lubricants can become baked onto the steel
surface during fabrication. Oil based fluids are not visible
during pre-treatment processing and may contaminate the
surface preventing the coating from forming. Cutting oils
should be cleaned from the surface prior to delivery.
Pitted surfaces will be evident after galvanizing.
Steel Coatings
The bond between the steel and zinc is unable to be
achieved if any form of substance remains on the steel
surface after chemical treatment. Resistant substances
which can prevent the coating from forming include
(however are not limited to) pre-existing zinc coatings,
paint, lacquer and adhesive residue from identification
labels and stickers.
•Adhesive Residue
Manufacturer’s steel identification stickers will deteriorate
during pre-treatment processing; however non visible
adhesive residue may remain and prevent successful
formation of the zinc coating. Stickers should be removed
and the immediate area prepared by suitable means to
remove the adhesive substance prior to despatch.
•Marking Pens
Paint pigmentation from marking pens may be resistant
to chemical cleaning. During pre-treatment processing
paint layers are removed, however, non-visible pigments
may remain. The zinc coating will form around the residue
pigmentation and remnants of workshop markings may
remain evident after galvanizing. Oil based paint markings
should be removed by suitable means from steel surfaces
prior to delivery for galvanizing.
Drilling lubricant can contaminate
the steel surface preventing
successful coating.
Oil based paint markings should be ground from the steel surface prior to hot dip galvanizing.
In some applications, small mating or threaded areas
may be required to be uncoated. This can be achieved by
applying a small amount of a suitable adhesive or sealing
product on the area creating a barrier to pre-treatment
acids and zinc. The following products will have varying
success in preventing zinc coatings from forming and some
clean up of the surrounding surfaces will be required by
the fabricator after galvanizing.
–Tapes high temperature tape / duct tape
–Sealants silicone adhesive sealant / petroleum gel /
household caulk
–Paints Maskote / Stop Galv
Application of a high
temperature tape or
sealants will prevent
zinc from forming in
small areas.
•Penetrant Dye for Welds
Dyes utilised for weld checks can create issues if unable
to be removed by pre-treatment chemicals. Dyes should
be removed from steel surfaces with a suitable paint
removing solution or by light sanding prior to despatch
for galvanizing.
•Painted Sections
Most pipe and tube sections manufactured in Australia are
painted with water based coatings which generally can be
removed within our process. Some local manufacturers
of pipe and tube products and most offshore producers
coat their product range with clear varnish or black
bituminous paint. These coatings are resistant to chemical
removal within our galvanizing plant and are required to be
abrasive blasted prior to delivery. To avoid additional costs
and extended processing times, hollow sections should
be stipulated that they be suitable for hot dip galvanizing
when ordering from your steel supplier.
All steel sections with powder coated, brush or spray paint
coatings must be abrasive blasted prior to despatch to
Hunter Galvanizing.
Dyes utilised to check for weld penetration
can contaminate the steel surface and should
be removed prior to delivery.
Primer paint coatings can be removed from most domestically produced pipe and tube sections during our process.
•Pre Existing Zinc Coatings
Pre existing zinc coatings must be stripped from all items
including in-line produced lengths of hollow section,
purlins, wire and mesh prior to hot dip galvanizing.
Additional charges are necessary for this procedure and
lead times may be increased. Some pipe and tube products
have an external light coating of zinc and a painted internal
surface. These items will require internal abrasive blasting
prior to delivery to our facility in addition to acid stripping.
Thermal Cut Edges
Flame, laser and plasma cutting will change the structure
of the steel composition in the immediate area of the heat
source. These areas may present thinner coating thicknesses
and a lack of adhesion, reducing the ability of the zinc alloy
layers to bond with the base metal.
The high temperatures utilised to cut material depletes the
alloying elements in surface of the steel. As discussed in
Hot Dip Galvanized Coatings the formation of the coating
structure relies on the alloying of iron and zinc in the
galvanizing bath. Should insufficient alloying elements be
present, the minimum coating thickness may not be able
to be achieved; and cohesion of the galvanized coating
will also be limited. To eliminate such issues, grind the heat
affected surface and bevel the cut edge.
Pre existing zinc coatings must be removed
prior to hot dip galvanizing.
Flame cut edges should be ground prior to
delivery for galvanizing.