Radiographic IQI Requirements for Structural Weld RT — AWS D1.1
How CWIs and NDT technicians select, place, and document image quality indicators for structural weld radiographic testing under AWS D1.1:2025. 155 characters.
Radiographic testing (RT) of structural welds has two distinct jobs: detecting weld discontinuities and demonstrating that the examination was sensitive enough to detect them. The image quality indicator (IQI) — sometimes called a penetrameter — does the second job. CWIs and NDT Level II technicians who understand IQI requirements avoid the common mistake of radiographing a structurally sound weld and then having the film rejected because the technique could not have detected a reportable flaw.
This guide covers IQI selection, placement, and documentation for structural weld RT governed by AWS D1.1:2025. Rule library based on AWS D1.1:2025; verify against your governing edition.
What an IQI Actually Certifies
An IQI does not measure weld quality. It measures the radiographic sensitivity of the technique — how small a linear void or thickness change the film would have recorded if one were present. If the specified IQI image is visible and legible on the radiograph, the technique is qualified. If it is not, the film does not constitute a valid examination, regardless of what the weld metal looks like.
This distinction matters for CWIs who review RT packages. A clean radiograph with a missing or unreadable IQI image must be retaken, not accepted.
Wire vs. Hole IQIs
AWS D1.1:2025 incorporates ASTM RT standards by reference. Two IQI designs are accepted:
Wire IQIs (ASTM E747): A set of progressively finer wires embedded in a radiographically transparent holder. The required wire is identified by number; visibility of that wire on the film confirms the technique meets the specified sensitivity. Wire IQIs are easier to read on welds with crowned reinforcement or complex geometry because the wires contrast against variable background density.
Hole IQIs (ASTM E1025): A flat plaque of the same material class as the subject, drilled with holes of defined diameter-to-thickness ratios. The 1T and 2T holes (where T is the plaque thickness) provide the two-step sensitivity call. Hole IQIs are common in pressure vessel and pipe work; structural shops see them less often but they are fully acceptable under D1.1.
Material class selection: IQIs must be made from material with similar radiographic absorption to the base metal. Carbon steel welds use IQIs from ASTM E747/E1025 Group 1 (iron or steel). Using an aluminum IQI on a carbon steel weld introduces a systematic error in the sensitivity call.
Sensitivity Requirements for Structural Welds
The standard for structural weld RT specifies IQI sensitivity in the form 2-2T: the wire number (or equivalent hole IQI) that represents approximately 2% of the nominal weld thickness, with the 2T hole visible. In practice, the NDT technician selects the IQI by looking up the weld thickness in the ASTM E747 or E1025 tables and choosing the IQI set that provides 2% sensitivity at that thickness.
For welds that vary in cross-section — such as a wide-flange flange-to-web joint with a groove weld adjacent to a fillet — the IQI is selected for the thickest cross-section under examination. If the thickness varies enough that one IQI cannot represent the full cross-section, the radiograph is broken into segments, each with its own technique and IQI.
Placement: Source-Side vs. Film-Side
Source-side placement (the IQI sits between the radiation source and the weld) is the standard. The IQI is placed on the source side of the weld, within the area of interest but not over a discontinuity that could mask the IQI image. This position is geometrically magnified by the radiation geometry, so a just-visible IQI image confirms better sensitivity than the same IQI placed on the film side.
Film-side placement is permitted when geometry prohibits source-side access — for example, the inside of a closed box section, or a double-wall exposure of a small-diameter pipe. Film-side placement must be identified by a letter "F" (or other designated marker) adjacent to the IQI image on the film, so the reviewer knows to apply the corrected sensitivity interpretation. Film-side placement achieves the same stated sensitivity only if the technique parameters compensate for the reduced geometric effect.
Placement within the image: The IQI must appear in the radiographic image with its identifying number legible. It cannot be placed so that it shadows an area of interest, but it must be within the area covered by the exposure. For groove welds, the IQI is typically placed on or immediately adjacent to the weld centerline.
Film Density and IQI Visibility Together
Film density and IQI visibility are both required, and they interact. Under AWS D1.1:2025, the acceptable density range is:
X-ray: 1.8 to 4.0 H&D
Gamma ray: 2.0 to 4.0 H&D
A film exposed to a density of 1.5 (too light) will likely fail both: the IQI may appear visible because contrast is low, but the technique has not demonstrated adequate sensitivity for detecting tight cracks. A film at density 4.5 (too dark) may show the weld clearly but the IQI wires are unreadable in the dense areas. Density measurement is taken through the weld crown or the base metal adjacent to the weld, not in the clear film area, to confirm the measurement location represents the examination volume.
Density meters used in production must be calibrated traceable to NIST or equivalent. A density step tablet is the standard reference for field calibration checks.
Multiple Exposures and Composite Images
Structural welds longer than the effective film length require multiple overlapping exposures. Each exposure must have its own IQI; a single IQI from an adjacent shot does not carry over. The overlap between exposures must be sufficient that no portion of the weld is examined only near the edge of a film, where geometric distortion reduces sensitivity.
For circumferential welds examined with a panoramic (central source) technique, one or more IQIs placed around the circumference confirm technique uniformity. Structural round hollow section joints — especially TKY tubular connections — may require this approach if the weld cross-section varies significantly around the circumference.
Documenting IQI Compliance in the RT Package
A complete RT record for a structural weld includes:
Technique sheet: radiation source, kV or Ci, source-to-film distance (SFD), exposure time, film type, screen type, IQI type and number used, date.
Radiograph identification: weld joint number, film number, examination area boundaries, orientation markers, IQI placement (source or film side), density readings.
Interpretation report: identity of the NDT Level II or III who interpreted, findings per AWS D1.1:2025 acceptance criteria, disposition (accept/reject/repair), and cross-reference to the examination record.
AISC-certified fabricators include the RT package in the audit packet alongside the WPS, PQR, and welder qualification records. CWIs reviewing third-party RT packages should verify that the technique sheet documents the IQI number used, the density was within range, and the IQI image was declared visible on each film — not assumed.
Common Errors That Invalidate Structural RT Films
Wrong IQI material: Using a copper IQI on carbon steel produces an overly optimistic sensitivity call. Always verify group/material.
IQI placed over a weld flaw: An IQI placed directly over a suspected discontinuity can partially mask the flaw image. Place the IQI adjacent to, not on top of, any area of suspected indication.
Missing identification: Films without readable weld ID, orientation markers, or IQI identification cannot be linked to a production record. The CWI cannot associate the film with a specific weld joint.
Film-side IQI without "F" marker: Film reviewed without knowledge of the placement type will be evaluated against source-side sensitivity criteria, potentially accepting a film that only achieved film-side sensitivity levels.
Density outside range before IQI reading: Density measurement should precede or accompany IQI visibility evaluation. A film outside the density range is an invalid examination even if the IQI image happens to be visible.
Practical Setup Checklist for Structural RT Setups
Before pulling the radiograph on a critical structural weld, run through this sequence:
Confirm IQI type (wire/hole) and material group matches the weld.
Select IQI number from thickness lookup; document on technique sheet.
Confirm placement (source-side preferred; mark "F" if film-side).
Set SFD to achieve penumbra (geometric unsharpness) within allowed limits.
Calculate exposure from kV, SFD, and density target using technique charts.
After developing: measure density in the weld area and confirm range before interpretation.
Confirm IQI wire/hole image is visible and document on the interpretation record.
Can we use hole IQIs instead of wire IQIs for structural weld radiography?
AWS D1.1:2025 accepts both wire IQIs per ASTM E747 and hole IQIs per ASTM E1025. The essential IQI sensitivity requirement (typically 2-2T) must be met regardless of which type is used. Wire IQIs are more common in structural shops because they span a broader weld thickness range.
Does the IQI have to be placed directly on the weld bead for structural RT?
Preferred practice is source-side placement on or adjacent to the weld. Film-side placement is permitted when geometric access prohibits source-side, but it must be noted on the radiograph. The IQI should represent the thickest part of the weld cross-section being examined.
What film density range is acceptable for structural weld radiographs under AWS D1.1?
AWS D1.1:2025 requires a minimum film density of 1.8 H&D for x-ray and 2.0 for gamma-ray sources, with a maximum of 4.0 for both. Density is measured through the IQI or the weld, not through the base metal only.
What happens if the required IQI wire or hole image is not visible on a production radiograph?
The radiograph is unacceptable as an examination record. The technique must be corrected — exposure time, distance, or kilovoltage adjusted — and the joint re-shot before an accept/reject interpretation can be rendered.