Not every structural weld requires 100% radiographic or ultrasonic testing. Knowing when spot inspection satisfies AWS D1.1 — and when you need full volumetric coverage — is one of the most practically useful things a CWI or QC manager can have clear before a job starts. The answer depends on weld category, structural loading type, and what the contract says.
Visual inspection is the baseline — always
Before discussing RT and UT sampling, the most important point: visual inspection is mandatory for all welds under AWS D1.1, regardless of weld category, loading condition, or NDE method. You cannot waive visual inspection. It is required to be complete before any other NDE method is applied, and it catches a significant percentage of weld defects on its own — porosity clusters, undercut, overlap, incorrect weld size, and crater cracks are all visible.
AWS D1.1 sets visual acceptance criteria based on weld category. For a detailed breakdown of those criteria, see visual acceptance criteria under AWS D1.1.
Weld category and loading type: the two variables that drive NDE scope
The most important variable in determining NDE scope is how the structure is loaded:
Statically loaded structures — Most building steel falls here: columns, beams, and braces in gravity-only systems without seismic demand classification. AWS D1.1 allows spot NDE for many weld types in this category. The code does not mandate 100% RT or UT for every CJP groove weld in a statically loaded structure.
Cyclically loaded structures — Bridges, crane girders, overhead lifting equipment, and any structure subject to repeated stress reversals. The code is more stringent here. CJP groove welds in primary tension members of cyclically loaded structures typically require more comprehensive NDE coverage, often approaching or reaching 100%.
The contract documents govern the final requirement. AWS D1.1 sets the floor; the EOR or owner can always require more. The code's role is to provide a framework; the EOR populates it with specific inspection designations for each weld category on the project.
CJP, PJP, and fillet welds: different rules apply
CJP groove welds in primary load-carrying members of cyclically loaded structures represent the highest-risk category and receive the most NDE attention. In statically loaded structures, the same CJP welds can often be accepted on the basis of visual inspection plus spot volumetric NDE — or visual only, depending on the joint and its function.
PJP groove welds and fillet welds generally require visual inspection only unless the contract specifies additional NDE. Magnetic particle (MT) or liquid penetrant (PT) testing may be specified for surface defect detection on fillet welds in certain critical applications, but RT or UT of fillet welds is uncommon in standard structural work.
Tubular connections — HSS and pipe — have specific weld inspection requirements that differ from those for flat plate and shapes. See tubular HSS weld procedure qualification under AWS D1.1 for the qualification context; the inspection requirements for tubular connections follow the same structural loading logic but with geometry-specific scan requirements for UT.
How spot inspection works in practice
Spot inspection is not random selection — it should be systematically assigned before production begins. A typical spot inspection plan specifies a percentage of welds in each category (for example, 10% or 25% of CJP butt welds in a particular joint family) and defines how those welds are selected.
Common selection approaches:
- Sequential: every Nth weld (every fifth, every tenth)
- Welder-based: the first weld of each day from each welder, or a fixed number per welder per shift
- Zone-based: all welds in a specified bay or connection zone selected for one RT setup
The goal of a systematic plan is a statistical sample that represents overall production quality. Cherry-picking "easy" welds or accessible locations introduces selection bias that defeats the purpose.
The expansion rule. This is the part of spot inspection that QC managers sometimes overlook: when a spot inspection reveals a rejectable discontinuity, the scope expands automatically. AWS D1.1 requires inspection of additional welds — typically adjacent welds or additional welds from the same welder. If those additional welds also contain rejectable discontinuities, expansion continues, potentially to 100% of the relevant lot.
The expansion rule makes spot inspection self-regulating. A shop producing consistently sound welds rarely triggers expansion. A shop with a systematic problem — incorrect preheat, a welder whose technique is degrading, or degraded consumables — will find spot inspection rapidly converting to full inspection, which is exactly the intent. Document every step of an expansion sequence: which weld triggered it, which additional welds were inspected, and the outcome.