Film radiography has been the dominant technique for volumetric examination of structural welds since the 1940s. The image quality is well understood, the acceptance criteria are calibrated to it, and most CWIs learned their RT interpretation on film. But storage costs, processing chemicals, film availability, and turnaround time are all pushing fabricators toward digital alternatives.
Computed radiography (CR) and direct digital radiography (DR) are both seeing wider adoption on structural steel projects. Before a shop or NDE contractor makes the switch, there are qualification requirements, procedure documentation obligations, and practical trade-offs worth understanding.
Film RT vs. digital RT: the core difference
Traditional film radiography uses silver-halide film as the detector. X-ray or gamma energy exposes the film; chemical processing produces a permanent, analog image. The image is read on a light box by a certified interpreter.
Digital techniques replace the film with a different detector:
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Computed Radiography (CR): Uses a flexible, reusable photostimulable phosphor (PSP) plate. The plate is loaded into a film-like cassette, exposed in the same geometry as film, then removed and fed into a laser scanner. The scanner reads the stored energy pattern and generates a digital image file. CR hardware is portable and relatively low capital cost compared to DR.
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Direct Digital Radiography (DR): Uses a flat-panel detector array — either a direct-conversion panel or a scintillator-coupled flat panel — that converts radiation to an electronic signal in real time. There is no plate to process; the image appears on a monitor during exposure. DR delivers immediate feedback, which matters for repositioning sources and shot optimization on the floor.
Both produce digital image files. Both require appropriate software for display, contrast enhancement, and measurement tools. And both require qualified image quality indicators (IQIs) to demonstrate that the technique meets sensitivity requirements.
What AWS D1.1:2025 requires for digital techniques
AWS D1.1:2025 permits digital radiographic examination provided the technique meets the same image quality (sensitivity) requirements as the film-based procedure. The key requirements:
IQI sensitivity: The technique must demonstrate the same wire IQI or hole IQI sensitivity that would be required for a film technique at equivalent geometry and source-to-film distance. Digital techniques can achieve equivalent or better sensitivity, but the setup must be qualified to demonstrate it — not assumed.
Written NDE procedure: A written procedure must document the digital technique, including the detector type, source-to-detector distance (SDD), exposure parameters, image processing steps, and archival format. The procedure is qualified before production use.
Equipment qualification: The detector, scanner (for CR), and display system must be qualified. This includes establishing the baseline image quality performance of the system and checking it at defined intervals during production.
Display and interpretation requirements: Digital images are interpreted on calibrated monitors, not light boxes. The monitor luminance, resolution, and ambient lighting conditions are part of the technique qualification. An uncalibrated monitor in a bright room does not meet the requirement.
For the specific code language and clause references, consult AWS D1.1:2025 directly and your NDE contractor — provisions can be updated in code cycles, and your project may have supplemental owner requirements that are stricter than the code minimum.
ASTM standards that underpin digital RT
AWS D1.1 references ASTM standards for the conduct of RT examinations. For digital techniques, the key ASTM standards are:
- ASTM E2002: Standard Practice for Computed Radiology (CR) for Examination of Weldments
- ASTM E2698: Standard Practice for Radiological Examination Using Digital Detector Arrays (DR)
- ASTM E747: Wire IQIs — same as for film, the reference for sensitivity demonstration
- ASTM E1734: Standard Guide for Radioscopic Examination of Metallic Castings (some provisions referenced for DR real-time work)
Your NDE contractor should be familiar with these standards and should incorporate them by reference in the written procedure.
Practical trade-offs: CR vs. DR vs. film
CR advantages over film: No chemical processing, no darkroom, immediate digital output, reusable plates reduce per-shot material cost. Plates can be formed to fit curved surfaces similarly to film.
CR disadvantages vs. film: Plate handling adds a step; scratched or damaged plates introduce artifacts. Scanning time reduces throughput compared to DR. Plates require calibration and periodic replacement.
DR advantages over CR and film: Real-time image display, fastest throughput, no plates to handle or process. Best for high-volume production environments with repetitive geometry (pipe circumferential seams on a large diameter, for instance).
DR disadvantages: Higher capital cost for the flat-panel detector. Panels are rigid — limited ability to fit curved or complex geometries. Larger physical footprint. More downtime impact if a panel is damaged.
Film advantages that are hard to replicate: Film is a permanent, inherently stable artifact. A film radiograph stored correctly can be re-read fifty years later with the same information. Digital images require active long-term storage management. Film is also flexible enough to handle complex geometries that DR panels cannot.
Where film still wins in structural fab: Complex joint geometries (T-joints, penetrations), field inspection where portability matters more than throughput, and projects with archival requirements that the owner's IT infrastructure cannot reliably support for decades.