Here at Premier Galvanizing we aim to answer any queries you may have about the services we offer. We are more than happy to discuss your requirements, advise on the best approach to meeting your needs and of course offer any advice generally about Galvanizing which you may have.
Check out the most common questions we are asked below – but of course, feel free to get in touch if we can help with anything else.
Why does my work sometimes need drilling before Galvanizing?
Galvanizing is a full immersion process and to facilitate this, all hollow section material requires a free flow of zinc through the whole structure and a means for air to escape. Without the necessary holes, it is not possible to galvanize hollow section successfully. Additionally, a mitred corner, gusset plate or recess that could pool liquid or trap air, will also require drilling for the same reasons. If pre-treatment chemicals are trapped inside a fabrication, there is a significant risk of explosion when the item is immersed in molten zinc.
For guidance on drilling requirements, please refer to our Design for Galvanizing fact sheet and booklet or call one of our offices for advice.
Why does the Galvanized coating sometimes have different shades of colour?
The bulk of the galvanized coating consists of alloy layers that are dull grey in colour. When work is withdrawn from the galvanizing bath, a layer of pure zinc usually cools on the surface to give the shiny silver appearance. However, variations in the surface chemistry of the steel have a major influence on its reactivity. With more reactive steels, the surface zinc layer continues to react after withdrawal and converts the zinc to alloy, thus giving a duller appearance. This can occur in isolated areas or across the whole surface. The variations in surface colour are not detrimental to the corrosion protection offered by the coating.
How long will the coating last?
This depends on the corrosion rate of the environment that the work is in and the thickness of the galvanized coating. Since atmospheric corrosion rates in the UK have fallen significantly over the last few decades, the general level of protection offered by a galvanized coating has in many cases, more than doubled. With typical corrosion rates averaging 1-2 microns per year, a coating life in excess of 30 years would not be uncommon.
What standard is my work galvanized to?
The standard for Hot dip galvanized coatings is EN ISO 1461:2. T009his supersedes the previous standard BS 729:1971 and all work is galvanized to this new standard.
BS EN ISO 14713:2009 gives additional guidance for protecting against corrosion of iron and steel in structures.
How thick will the coating be?
This depends on the material thickness and the type of material used. The following is a summary of mean coating thickness for the most common materials:
Steel ≥ 6mm thick – 85µm
Steel ≥ 3mm to < 6mm – 70µm
Steel ≥ 1.5mm to < 3mm – 55µm
Tables 2 and 3 within EN ISO 1461:2009 give the full details for both conventionally dipped and centrifuged work respectively.
Is it possible to get a thicker coating than the standard requires?
In order to achieve a thicker coating, the steel would usually require blasting to SA2.5 with a G24 chilled iron grit. For regular products or larger contracts, it may be possible to specify controlled silicon steels that are more reactive and give a controlled level of reactivity above standard. Please contact us at one of our offices for further information.
If the coating is scratched and scuffed will it last as long?
Hot dip galvanized coatings have excellent abrasion resistance. In fact, the outer zinc layer is soft enough to absorb impact and abrasion while the alloy layers that are metallurgically bonded to the steel, are harder than the steel substrate. Minor abrasion will have little impact on the life of the coating.
If I have to do any repairs or alterations on site, can the galvanizing be repaired?
The most common method for repairing galvanized coatings is to use a suitable zinc rich paint. This needs to be applied in accordance with the manufacturer’s instructions and to a thickness equal to or 30µm more than the surrounding coating depending on whether or not the item is to be over coated. An alternative method is to have the area zinc thermal sprayed to the required thickness.