AS/NZS 1554 weld categories: what SP, GP and FP actually change
Last reviewed
Short answer
SP (structural purpose) and GP (general purpose) are the two weld categories in AS/NZS 1554.1 Clause 1.6. The choice is structural before it is procedural: AS 4100 assigns a capacity reduction factor of 0.8 to an SP weld and 0.6 to a GP weld, so specifying GP gives up 25 per cent of the weld capacity for the same weld size. SP is selected where a weld is stressed above 50 per cent of the relevant maximum permissible stress or is subject to dynamic loading; GP covers welds below that threshold and non-structural applications. SP also carries tighter acceptance limits and heavier inspection. FP (fatigue purpose) is a separate category in AS/NZS 1554.5. The designer selects the category and nominates it on the drawings.
Key numbers
- SP capacity factor (AS 4100)
- 0.8
- GP capacity factor (AS 4100)
- 0.6, which is 25 per cent less capacity for the same weld size
- SP selected where
- The weld is stressed above 50 per cent of maximum permissible stress, or is subject to dynamic loading
- GP selected where
- The weld is stressed at or below 50 per cent, or the application is other than structural
- Inspection and acceptance
- SP has tighter Table 6.2.1 / 6.2.2 limits and a heavier Table 7.4 sample than GP
- FP
- Fatigue purpose, AS/NZS 1554.5, for structures subject to high levels of fatigue loading
The category is a design decision with a capacity consequence
AS/NZS 1554.1 states the intent plainly in its preface: the designer selects the category suited to the severity of the service and nominates it on the drawings. Clause 1.6 then gives the selection criteria, and they are written in terms of stress and loading rather than inspection.
The reason this matters beyond paperwork is that AS 4100 prices the two categories differently. The capacity reduction factor for a fillet weld is 0.8 for SP and 0.6 for GP, so an SP weld carries 25 per cent more design capacity than a GP weld of identical size. A connection designed on SP capacity and then fabricated and inspected to GP is undersized, not merely under-documented.
Where a drawing is silent the category has to be resolved with the designer rather than assumed. The standard does allow one direction of movement after the fact: a weld nominated SP but not complying with that category may be considered a GP weld, provided the requirements of the design standard are still satisfied and the principal has agreed.
- GP selection criteria (Clause 1.6)
- Essentially statically loaded and designed to AS 4100 or NZS 3404.1; stressed to not more than 50 per cent of the maximum permissible stress in AS 3990; or the application is other than structural
- SP selection criteria (Clause 1.6)
- Essentially statically loaded and designed to AS 4100 or NZS 3404.1; stressed to more than 50 per cent of the maximum permissible stress in AS 3990; or subject to dynamic loading within the limits of Clause 1.1
- AS 4100 capacity reduction factor
- 0.8 for SP, 0.6 for GP
- Downgrading SP to GP
- Permitted where the design standard is still satisfied and the principal has agreed
What changes in inspection between SP and GP
Both categories need a qualified procedure and a qualified welder. What differs is the acceptance limits for imperfections in Tables 6.2.1 and 6.2.2, and the suggested examination extents in Table 7.4.
Visual scanning under Clause 7.3 applies to every weld in both categories. Detailed visual examination and volumetric sampling are heavier for SP than for GP. The full Table 7.4 matrix, sampling program and method selection live in the NDT requirements guide.
- Visual scanning, GP and SP
- 100 per cent (Clause 7.3)
- SP versus GP sample
- SP uses the heavier Table 7.4 band for visual examination and surface methods; volumetric RT/UT is suggested for SP only
- Volumetric examination trigger
- For SP butt welds, radiographic or ultrasonic examination applies where it is required by the principal and specified on the drawings (Clause 6.2.1)
FP is a different part of the standard, not a third tier of 1554.1
Fatigue purpose welds belong to AS/NZS 1554.5, which covers welding of steel structures subject to high levels of fatigue loading. It is not simply a stricter SP. The workmanship, inspection and acceptance regime is built around crack initiation from cyclic loading, so surface condition and transverse defects matter far more than they do in a statically loaded SP weld.
Even within 1554.1 the fatigue concern is visible. Table 7.4 recommends 100 per cent visual examination for SP welds that are subject to fatigue loading, form part of a seismic-resisting system, or comply with NZS 3404.1. Where a structure is genuinely fatigue governed, the work belongs under 1554.5 rather than under a hardened reading of 1554.1.
Choosing the right part of the AS/NZS 1554 series
Weld category only makes sense once you have the right part of the series. Applying 1554.1 essential variables to quenched and tempered or stainless material is a common and serious error.
- AS/NZS 1554.1
- Welding of steel structures. Carbon and carbon manganese steels. Categories SP and GP
- AS/NZS 1554.4
- Welding of high strength quenched and tempered steels
- AS/NZS 1554.5
- Welding of steel structures subject to high levels of fatigue loading. Category FP
- AS/NZS 1554.6
- Welding stainless steels for structural purposes
How ForgeQM enforces the category
ForgeQM treats AS/NZS 1554.1, 1554.3, 1554.4, 1554.5 and 1554.6 as mandate standards. That means the weld category and material scope are checked when a PQR or WPS is activated, approved, or used to generate a WPS, and the action is blocked rather than merely flagged if it does not hold. Any override is recorded against the document with a reason so it survives an audit.
The Qualification Testing Checker takes the category as an input and returns the mechanical test specimen counts from Table 4.7.1 along with the qualified ranges, so the category feeds the test plan rather than being recorded after the fact.
Frequently asked questions
Is SP always better than GP?
SP is more demanding, not universally better. Specifying SP everywhere raises cost and inspection load without improving a structure whose welds are not critical. But the choice is not free either way: AS 4100 gives an SP weld a capacity reduction factor of 0.8 against 0.6 for GP, so downgrading to GP costs 25 per cent of the weld capacity. The category should follow the structural function of each weld, which is why it is a design decision recorded on the drawing.
Does an SP weld always need radiography or ultrasonic testing?
No. Under Clause 6.2.1, radiographic or ultrasonic examination of SP butt welds applies where it is required by the principal and specified on the drawings or other documents. Table 7.4 suggests an extent of 0 to 10 per cent for SP and nil for GP, and it is guidance on a suggested extent rather than a mandatory percentage. What is applied to every weld in both categories is 100 per cent visual scanning under Clause 7.3.
Can one WPS cover both SP and GP welds?
A procedure qualified to the SP requirements will generally satisfy GP work as well, since SP is the more demanding category. The reverse does not hold: a GP qualification does not support SP production. The mechanical test matrix in Table 4.7.1 differs between the two, so check the qualification evidence rather than the WPS heading.
What category applies to stainless steel structural welds?
Stainless structural welding falls under AS/NZS 1554.6 rather than 1554.1, so the SP and GP categories of 1554.1 do not carry over unchanged. AS/NZS 1554.6 brings its own workmanship gates and directs ultrasonic testing to ISO 22825 rather than AS 2207, and penetrant testing is generally preferred over magnetic particle testing on austenitic material.
Sources
This guide is written against the published standards below. Standards are revised, and project specifications override general guidance, so confirm clause numbers against the edition your contract names before relying on them.
- AS/NZS 1554.1:2011 Structural steel welding, Part 1: Welding of steel structuresClause 1.6 weld categories and selection criteria, Clause 6.1 categories of welds, Clause 6.2.1 methods of inspection, Tables 6.2.1 and 6.2.2 permissible levels of imperfection, Clause 7.3 visual scanning, Table 7.4 suggested extent of non-destructive examination.
- AS 4100 Steel structuresCapacity reduction factors for welds, which differ between SP and GP and are the design consequence of the category.
- AS/NZS 1554.5 Structural steel welding, Part 5: Welding of steel structures subject to high levels of fatigue loadingCategory FP, for structures subject to high levels of fatigue loading.
- AS/NZS 1554.6 Structural steel welding, Part 6: Welding stainless steels for structural purposesStainless scope, workmanship gates and ultrasonic testing to ISO 22825.
- AS/NZS 1554.3 and AS/NZS 1554.4Reinforcing steel and quenched and tempered steel scope, which sit outside AS/NZS 1554.1.
Related guides
- Weld NDT Requirements and Inspection ExtentsVisual scanning is always 100%. Beyond that, NDT extent comes from the governing standard, the weld category or construction class, and the material. AS/NZS 1554 structural rules and a compact AS 4037 class table, with method selection logic.
- WPS vs PQR vs WQR: What Each Record ProvesA PQR records a test weld and its results, a WPS turns that evidence into welding instructions with qualified ranges, and a WQR proves an individual welder can work to it. Written order, what carries between them, and the AS/NZS 1554.1 ranges.
- Welding Qualification Ranges ExplainedA qualification test on one plate qualifies a band of production work. How welder thickness, position, joint type, process and material group ranges are derived, where they differ from procedure ranges, and what triggers reapproval.
Stop checking this by hand
ForgeQM applies the AS/NZS 1554 series as checks while you write the record, not after. Qualification ranges are generated from the PQR, NDT extents come back with the clause they came from, and job data carries across every document through to the MDR.
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