You may be familiar with using EN ISO 1461 for the specification of hot dip galvanizing for your steelwork. A less familiar – but just as important standard – has recently received a comprehensive revision, EN ISO 14713-2 : 2020 – Zinc coatings – Guidelines and recommendations for the protection against corrosion of iron and steel in structures – Part 2: Hot dip galvanizing
The new revision includes some important design features specific to the hot dip galvanizing process, particularly best practice covered in the informative ‘Annex A – preferred design of articles for hot dip galvanizing’. Some important updates include:
- Design for narrow gaps between parts and venting and drainage in structural hollow sections.
- A table giving recommended size and location of vent and drain holes for hollow sections
- Recommended minimum edge distance of vent and drain holes for welded box sections
- Surface preparation to ensure understanding and consistent delivery of a high-quality coating.
- Process issues pertaining to single dip design and article size, and arrangements for lifting and handling of work via lifting lugs.
- Adaptation of the article design and construction for the hot dip galvanizing process
- Ultra-low silicon reactivity/material composition clarity – (See Table 1, note 4 of the standard)
It is important that steelwork is sent to the galvanizer in a suitable condition for processing as some surface contaminants will not be removed by the normal pre-treatment process and can result in uncoated areas. EN ISO 14713-2 lists a variety of such products including oil, grease, paint, welding slag, labels, glue and marking materials. In addition, if oil based or silicone based weld anti-spatter sprays are used they may burn onto the steel surface resulting in uncoated areas. Silicone free sprays (water based or water soluble) are preferred.
Other important aspects that need to be considered include an obvious but important point; work sent for galvanizing will fit into the galvanizers’ bath and that adequate provision is made for jigging the work by way of holes and/or lifting lugs as appropriate. Be aware that the use of low silicon steels (0.01% max) may result in the steel having a low reactivity such that a reduced coating thickness below that specified in EN ISO 1461 might be achieved.