We received the following question related to Galvanizing Fasteners, we thought you may be interested in the response.
I have a few questions for you… As I understand it, AS 1214 requires only a minimum average of 52.5microns for all bolts.
So some questions come to mind:
Is this irrespective of size (bolt diameter)?
Can this be increased, if so, under what conditions?
If not, what is typically done to increase life of HDG bolts considering they may have significantly less coating thickness relative to the steelwork section.
AS 1214 was updated in 2016 and is now AS/NZS 1214 and is essentially a direct copy of the international standard ISO 10684. It has a requirement of a minimum batch coating thickness of 50 microns.
The coating thickness is irrelevant of bolt size. The reason for this is that the bolts are galvanized in a machine that spins the excess zinc off the items when they are withdrawn from the bath (while the zinc is still molten), thus leaving the alloy layers.
If you look at the new standard you will see a table of recommended maximum coating thicknesses which will avoid interference between the internal nut thread and external bolt thread when maximum tolerance positions occur. Therefore, it is possible that some manufacturers can offer an increased thickness. Most bolts are made overseas, so this is not an area of focus for us in Australia and we do not have any specific details here. I would say that, unless you have a large requirement to warrant a special order, it is unlikely that the coating thickness on stocked items can be guaranteed to be a ‘desired’ coating thickness.
If a longer maintenance free life is required for commercially available galvanized fasteners, there is a well proven protective non-corroding cap system patented by Radolid made from UV resistant linear-low density polyethylene (LLDPE), with a 15 year warranty. Details are available at https://radolid.de/en/produkte/. There are several distributors in Australasia including https://www.anodeengineering.com/product/type-sw/ and there are also several other international manufacturers of ‘copy cat’ clip-on caps but with reduced range of sizes and less assured quality of manufacture. The Radolid caps will fit any metric bolt made to conform to AS/NZS 1252.1.
There are also metallic versions available in plated steel, stainless steel or aluminium designed in Italy called ‘BoltShield’. These are available in Australia through https://www.specialisedforce.com.au/product/boltshield-protection-caps. These can be filled with a corrosion inhibiting grease, could also be painted if required and would allow for future maintenance checks on the nuts or easier access for replacement if ever required. If considering the electroplated version, be aware they are unlikely to offer any significant corrosion protection and you will also need to consider galvanic corrosion issues if you are using anything other than bare steel or galvanized/electroplated coatings on the caps.
If you have a question that is not listed here, would like more information or would like to discuss a specific scenario, please contact us.