Common AS/NZS 1163 Specification Errors in Procurement and How to Catch Them Before Fabrication
Structural steel hollow sections specified to AS/NZS 1163 are a commodity item in Australian and New Zealand construction — they’re widely available, consistently priced, and straightforward to order. That familiarity is also why specification errors go unnoticed until fabrication is underway or material has already arrived on site. The mistakes that follow are not unusual. They’re the ones that appear repeatedly, often because someone assumed the standard details would sort themselves out.
Ordering by nominal size without verifying the standard size series
AS/NZS 1163 defines specific dimensional series for CHS, SHS, and RHS. The available sizes are not continuous or arithmetic — you cannot order any arbitrary dimension and expect it to exist. CHS outside diameters follow a standardised series (48.3, 60.3, 76.1, 88.9, 101.6, 114.3 mm, and so on). RHS and SHS outer dimensions follow a similar set of standardised sizes.
The procurement error is specifying a “100 mm OD CHS” when the actual available size in the standard is 101.6 mm OD. The difference seems trivial, but if the design had specific section properties in mind, or the detail has been drawn with 100 mm in mind, this will not match. The fabricator will typically substitute the nearest standard size — but whether that substitution is flagged to the design engineer or silently made is not guaranteed.
Before finalising a specification or purchase order, cross-reference the size against the dimension tables in AS/NZS 1163 to confirm it exists in the standard. If the required size isn’t listed, either the design needs to be revised to the nearest standard size or an alternative product standard needs to be referenced.
Omitting the grade, or assuming C350L0 when the design used C250L0
The grade designation in AS/NZS 1163 — C250L0, C350L0, or C450L0 — carries the minimum yield strength and the impact toughness requirement. A purchase order that specifies only “SHS to AS/NZS 1163” without a grade leaves the supplier free to ship whichever grade they have in stock, which will often be C350L0 for common sizes and C250L0 for lighter sizes.
The reverse problem also occurs: a design based on C250L0 capacity gets C350L0 delivered. While C350L0 has higher yield strength, if the section class limits or design checks were based on C250L0 properties (including the lower yield for compact section classification), using C350L0 without re-checking the design isn’t necessarily conservative — higher yield can push a compact section into the non-compact or slender range under AS 4100 section classification rules.
Specify the grade explicitly. If the design was done to C350L0, the purchase order must say C350L0. If the engineer has deliberately used C250L0 for a reason (connection details, lower yield for certain ductility requirements), that choice must survive into the procurement specification.
Missing the L0 impact toughness requirement
The “L0” suffix in the grade designation indicates that the steel must demonstrate a minimum Charpy impact energy at 0°C. This requirement exists to ensure the hollow section has adequate toughness in environments where low temperatures could trigger brittle fracture. For most climate zones in Australia and New Zealand, L0 is the appropriate requirement and is already embedded in the standard grade designations.
The error occurs when specifying hollow sections sourced from offshore mills that supply product to their local standard rather than AS/NZS 1163. A C350-equivalent grade from a non-certified mill may not include impact testing at all. The Mill Certificate for such material won’t contain an L0 test result because the test wasn’t performed.
When receiving material from offshore supply sources, confirm that the Mill Certificate explicitly records Charpy impact test results at 0°C meeting the L0 requirement. A certificate that shows strength values only — without impact data — is not AS/NZS 1163 compliant for any of the standard grade designations.
Accepting a product data sheet instead of a heat-specific Mill Certificate
A product data sheet from a distributor or manufacturer’s catalogue states the nominal properties of their product range. It is not a material test report. A compliant Mill Certificate for AS/NZS 1163 hollow sections should include: the heat or cast number of the steel, actual chemical composition by heat, actual tensile test results (yield strength, ultimate tensile strength, elongation), Charpy impact test results at 0°C, and the dimensions of the product from that heat.
A data sheet saying “this product meets AS/NZS 1163 C350L0” is a commercial claim, not a compliance document. For structural applications subject to engineering certification, quality plans, or third-party inspection, a heat-specific Mill Certificate is required. If a supplier cannot provide one, they cannot demonstrate that the specific material they delivered meets the standard.
Not checking the wall thickness tolerance before connection design
AS/NZS 1163 allows a wall thickness tolerance of −10% on the nominal value. A 6.0 mm nominal wall section can legally have a wall as thin as 5.4 mm. This affects the section area, the second moment of area, and therefore the section capacity calculated in design.
Connection designs that rely on the hollow section wall for load transfer — welds to the tube wall, through-bolts bearing on the wall, end-plate connections — should be designed for the minimum wall, not the nominal. A connection detail that works at 6.0 mm wall but is marginal at 5.4 mm will be inadequate for some portion of any delivery that exercises the full minus tolerance.
For sections where the wall thickness is critical to connection performance, the purchase specification can invoke a tighter wall thickness tolerance as a supplementary requirement. This narrows the tolerance band and reduces but doesn’t eliminate the variation.
Specifying RHS without indicating orientation
An RHS designation like “150 × 100 × 6.0 RHS C350L0” tells the supplier what to deliver but doesn’t tell the fabricator how to orient it. If the design intent is for the 150 mm dimension to be the depth (vertical, carrying primary bending), that must be shown on the fabrication drawing. A fabricator who places the section with the 100 mm dimension vertical — perhaps because a connection detail was drawn that way — has installed a section with significantly lower bending resistance about the primary axis.
This is not a material nonconformance — the section delivered is correct. It’s a fabrication and detailing error that originates in an under-specified drawing. The fix is to dimension the section clearly on structural drawings and mark the orientation explicitly, particularly for RHS beams and horizontal members.
Reviewing the AS/NZS 1163 compliance guide before finalising a procurement specification gives you the dimensional series, grade requirements, and tolerance parameters to check against. Most of the errors above are caught at the specification stage — catching them after fabrication is significantly more expensive.
