Galvanizers Association has provided authoritative information and advice on hot dip galvanizing to specifiers since it was first established in 1949. For many years this information has been used to educate and inform professionals within the construction industry through the provision of CPD (Continuing Professional Development) Presentations that the Association has been providing. GA were founder members of the RIBA CPD Providers Network and continue to work with RIBA to educate existing and new entrants to the industry.
In light of celebrating the 25th anniversary of HDG Magazine, we thought readers would be interested in the typical questions raised over that period of time.
What is the difference between hot dip galvanizing and galvanizing?
The term galvanizing does not really describe a coating and it has become a bit of a generic term. Hot Dip Galvanizing is the immersion of clean steel into a bath of molten zinc to obtain a coating that is metallurgically bonded to the steel.
What is cold galvanizing?
There is no such thing as cold galvanizing, it does not exist as a process. The use of a zinc rich paint is sometimes wrongly termed as cold galvanizing.
Can I weld two pieces of hot dip galvanized steel together?
Yes, as long as the right procedures are carried out it can be done successfully. We recommend that the coating is ground off before welding is carried out.
How long does hot dip galvanizing last?
A major advantage of hot dip galvanizing is that it has a long history, and therefore is a tried and tested method of corrosion protection with many monitored real world examples in use. Atmospheric performance will be dependent upon many factors, including location and coating thickness, but a very general average for the UK and Ireland would be 50 to 60 years.
Why do I sometimes get a variation in the appearance of a hot dip galvanized coating?
Variations occur due to the fact that a hot dip galvanized coating is a natural reaction between steel and zinc, the appearance being largely governed by the chemistry and quality of the steel that is being galvanized. In some ways the appearance of a galvanized coating is similar to that of timber and brick in that natural variations can occur.
What is the spangle that I sometimes see in the coating, is there a specification to obtain this?
The spangle is zinc crystals that form within the coating and vary in size and colour. They are a reflection of the chemistry of the steel that is being galvanized and the cooling rate after processing. For a batch hot dip galvanized product the spangle can not be specified.
Is it true that hot dip galvanizing can self heal itself?
Yes, a hot dip galvanized coating can offer sacrificial protection over a distance of up to 5 mm. In addition there will be no sideways creep of corrosion underneath a damaged area.
Can I paint on top of hot dip galvanized steel?
Yes, painting and powder coating can be successfully carried out as long as an appropriate pretreatment has been conducted. These include chemical or mechanical pretreatment, or alternatively a direct application paint might be applied. There is no technical reason that prevents paint from adhering to a zinc surface.
How long does it take to hot dip galvanize a piece of steel?
Technically the actual hot dip galvanizing process is very quick, the steel only needs a few minutes of immersion within the galvanizing bath to obtain the coating although from a logistics view point your work will have to be processed in a queue. The average turnaround time in UK and Ireland is three days although some individual plants do offer a 24 hour turnaround at a slight premium.
Can you recycle steel that has been hot dip galvanized?
Yes, there is no issue in recycling steel that has been hot dip galvanized, in fact many thousands of tonnes of zinc are recycled as a by product of recycling hot dip galvanized steel.
Is there such a thing as regalvanizing?
Yes, steel that has been previously hot dip galvanized can be regalvanized. This is something that can be done when the coating is reaching the end of its life, the major advantage being that by regalvanizing you are saving on the manufacturing of a new product.
Our main building cpd presentation ‘Corrosion Protection of Steel by Hot Dip Galvanizing’ gives an overview on galvanizing. The presentation is 45 minutes long and includes information on:
– Introduction to Hot Dip Galvanizing
– The galvanizing process
– Coating characteristics and performance
– Designing for the process
– Case studies
As a result of our initiative for galvanizing in sustainable construction, we have developed an online version of our CPDs. Using the latest technology to deliver the same high quality presentations via the internet.
To book a RIBA approved CPD with us please contact Carla Stanton by email: firstname.lastname@example.org or by telephone: +44 (0)121 355 8838