Weld category (GP / SP)

Weld category is the AS 4100 / AS/NZS 1554 classification of a structural weld that sets the quality and inspection it must meet. The two categories are GP (general purpose) and SP (structural purpose), and which one applies is shown on the engineer’s connection details.

The categories reflect how critical the weld is:

• SP (structural purpose): the higher category, for welds carrying significant or critical structural load. It has tighter acceptance limits (on defects, profile, and penetration) and more inspection (visual plus, where specified, non-destructive testing).
• GP (general purpose): for welds in less critical situations. The acceptance criteria are more relaxed and inspection is lighter.

The point is that “a weld” is not just a weld: the same joint specified SP must be made by a qualified welder to a procedure and inspected to the tighter standard, while a GP weld is held to less. Specifying or building an SP weld as if it were GP (no qualified procedure, no inspection) is a real structural defect, not a shortcut, and it is invisible once painted.

For a builder or fabricator the practical points are to read the weld category off the connection details (it will be noted, e.g. “all welds SP unless noted”), to use a welder qualified for the category and procedure, and to allow for the inspection an SP weld requires (and to keep the records). On site, field welds to a structural connection are an inspection point. If a drawing does not state the category, ask the engineer rather than assuming GP, because the default on structural connections is usually SP.

Also known as: Weld quality category, GP weld, SP weld.

Category: Structural steel / Welding.

Related

• AS 4100 steel structures
• Hollow section

See also

• Snug-tight

References

• AS/NZS 1554.1 Structural steel welding, Standards Australia (verified 2026-06-04)

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Last updated: 2026-06-04. Verified: 2026-06-04. Quarterly review for currency.