AS/NZS 5131 covers the construction (fabrication and erection) of structural steelwork. It defines four 'Construction Categories' (CC1 through CC4) that scale up in inspection rigor as the consequence of failure increases.
For most residential gate work, CC1 is the appropriate category: low-consequence failure, basic visual weld inspection, no formal welder qualification record. Commercial gate work and balustrades on multi-storey buildings step up to CC2 or CC3, with formal weld procedure qualifications and recorded inspections.
The standard also covers material traceability, painting and coating systems, and tolerances on fabricated work. A Form 16 engineering certification on a commercial gate will typically reference an AS/NZS 5131 construction category.