The achievement of a quality hot dip galvanized coating, for general and architectural use, is dependent on many issues, some controllable and some not. This checklist addresses the issues that can be controlled by the designer and those controllable by the galvanizer.
In the case of large contracts, the galvanizer should be involved at the programming stage with the fabricator and the end user. Hot dip galvanizing is normally the final process after fabrication and prior to delivery and erection. If sufficient time for hot dip galvanizing, cleaning, fettling and inspection is not provided in the overall programme, costly delays may occur at the erection stage.
SPECIFIER GALVANISING CHECKLIST
Discuss requirements with Galvanizers Association and/or the selected galvanizer/s before designing commences.
The specifier or designer to ensure all steelwork contractors are informed in writing of the architectural hot dip galvanizing requirements prior to the finalization of the tender.
Make the requirements known to the galvanizer, in writing, together with a sketch or sample, before placement of the order. Further discussion with the galvanizer may be required.
Make use of the Association wall chart – “Design for Hot Dip Galvanizing”
Choose correct steel type. If possible all parties related to the project to purchase the specified steel from the same or specified suppliers. Insist on the steel chemical analysis certificates for record purposes and issue copies to the galvaniser.
Ensure components can be dipped in a single immersion or alternatively discuss the impact of double end dipping with the selected galvaniser / Association.
Optimize size of filling, draining and vent holes
Optimize position of filling, draining and venting holes.
Should painting of the hot dip galvanizing be specified, ensure that instructions stating “No passivation is required – substrate is to be painted”, is handed to the galvaniser, at order stage, unless specifically discussed and excluded.
Select significant surfaces, highlight on drawing or sketch and discuss with galvaniser / Association.
If necessary, hot dip galvanize a sample and establish acceptance / rejection criteria.
Specify the correct temporary-marking pen for fabrication marking.
Ensure that if permanent marking, such as welded lettering is used it will be appropriately hidden from final view.
If deemed necessary, to minimize handling damage ensure correctly positioned lifting lugs are provided or if not acceptable, soft lifting slings are used, by all parties, including the galvaniser, the transporter, the off loader and the erector, etc. The use of the former is possibly more appropriate.
Specify welding that is fit for purpose; do not allow over welding.
Should stick welding be used, ensure that all weld slag is comprehensively removed by abrasive blasting or grinding prior to delivery to the galvanizer. (Excessive weld porosity can have a marked effect on the quality of the hot dip galvanized coating).
If the build-up of zinc at a weld is unacceptable for aesthetical reasons, request that the correct welding wire or rod be used. Some welding materials are reactive wrt hot dip galvanizing and can result in a thicker coating on the deposited weld.
Simplify componentry – Simple structures – Better coating quality
Complex structures – Harder to manipulate in the galvanizing bath, more control, cleaning and fettling necessary.
Simplify complex structures by making use of bolting where possible or alternatively design for after galvanizing welding, by using a suitable mask such as “Galvastop”, which can be easily cleaned, successfully welded and correctly repaired.
Discuss packaging / dunnage requirements with the galvanizer during transport and ensure that ample site stacking facilities are provided. A hot dip galvanized coating is applied in a factory and then transported to site where frequently the components are thrown off the truck. Inappropriate offloading may lead to unnecessary mechanical damage of the coating. As the components are generally not wrapped, coating discolouration due to contaminants being deposited by wet trades, i.e. angle grinding of wet clay bricks in the presence of hot dip galvanized components, should be prevented.
Discuss the appropriate repair method, if repair is deemed to be necessary, with the galvanizer. Silver spray paint is not acceptable. The silver spray paint may be initially more aesthetically acceptable while the hot dip galvanized coating is shinny, but will ultimately stand out and be aesthetically unacceptable, when the hot dip galvanized coating begins to weather to a matt dull grey appearance. Furthermore, most silver spray paints do not provide the same protection as a good zinc rich epoxy for repair purposes.
Discuss the maximum size of coating repair allowable when alterations or adjustments are made on site, with the appropriate contractors.
Discuss inspection of the components prior to these leaving the galvanizer’s premises.
Ensure that a certificate of conformance in accordance with the specification, has been obtained from the galvanizer.
Ensure that selected galvanizers use their appropriate identification paint, (if acceptable to the client) before delivering the components to site. Furthermore, identification paint is to be applied only to areas identified on the drawings by the architect or consultant or if not available in non-significant areas, particularly if the component is not to be over coated with a paint system.
Allow sufficient time for the hot dip galvanizing process to take place, ideally 3 to 7 working days, unless other arrangements have been made.
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