A specification that calls for class B doesn't ask for CR or for DR. It asks for a certain wire of the image quality indicator (IQI) to be visible and for the normalized signal-to-noise ratio to stay above a floor that ISO 17636-2:2022 sets by source and wall thickness. Take the table of the first edition, the 2013 version described by BAM in Berlin. Class B called for 150 below 50 kV, for example, and 100 with an iridium source on walls up to 50 mm. Those requirements, far more than the technology named on the quote, decide whether an exposure is accepted or shot again.
Computed radiography (CR) and direct digital radiography (DR) get there by different routes, and each one gives way at its own point. A phosphor plate's resolution depends partly on how the scanner reads it. A flat panel has a fixed effective pixel and a minimum wall thickness below which class B won't come out anyway. For a lab or shop moving off film, that's where the comparison starts, well before the price list.
Two acquisition chains, two response times
In CR, film gives way to a photostimulable phosphor plate, the imaging plate, exposed in a cassette much like film. Absorbed energy stays trapped in the phosphor as a latent image until a scanner releases it point by point with a laser, collects the emitted light and turns it into a file. The plate is then erased with bright light and goes back into its cassette. In DR the detector is a digital detector array (DDA): a scintillator converts X-rays into light read by an amorphous-silicon or CMOS photodiode matrix, and the image arrives in seconds with the part still in position.
Examination practices follow the same split, ASTM E2033/E2033M-24 for CR and ASTM E2698-26 for DDAs, while for welds ISO 17636-2:2022 covers both and requires detection sensitivity equivalent to film in the same class. Between the two technologies, what changes is the time from exposure to decision. The quality target stays exactly where it was.
CR holds its ground where geometry changes every day
A phosphor plate bends inside a cassette, wraps around a pipe and slips into a repair area a rigid panel can't reach. Shops coming from film change scanner and procedure without scrapping their cassettes, and spend in stages instead of all at once. BAM's 2007 paper adds a field observation: plates cope well with mobile work in bad weather and have no energy or dose limits, while digital panels do best where temperature and humidity are stable.
That flexibility is paid for in resolution. In 2014 Ewert and Zscherpel reported detector basic spatial resolution between 40 and 160 µm for CR systems in NDT use. High-definition plates developed for dental radiology and mammography were already below 25 µm in 2007, useful on thin walls at low voltage. A CR system's class is assigned under ISO 16371-1:2011, from IP 1 to IP 6, by combining a minimum normalized SNR, ranging from 130 down to 43, with the measured SRb. The full designation also carries that value in micrometers. According to the same authors, every NDT CR system available in 2014 already exceeded the SNR required for the top class, which leaves resolution and exposure time as what separates one system from another. Beyond welds, for metallic materials in general, CR technique is described in ISO 16371-2:2017, which replaced the old EN 14784-2 and takes over the selection tables of ISO 17636-2. Why the class belongs to the whole chain of plate, scanner and readout settings, rather than the plate alone, is explained in our piece on who decides acceptance levels.
Two practical points set CR apart from film. Plates, like scintillator panels, are more sensitive to low-energy scatter, and for steel BAM recommended lead screens about three times thicker than those used with film. The latent image also fades as time passes between exposure and readout: the 2022 edition of ISO 17636-2 added a note on exactly this in the annex linking gray value and signal-to-noise ratio.
DR pays off when the same welds come back every day
On the direct digital side the gain is in the cycle: no intermediate readout, an image while the part is still in position, an archive that fills itself. There's also a quality advantage CR can't match. Panels are calibrated with dark and flat-field images, including at several levels, and this correction removes almost all of the fixed-pattern noise of individual pixels. BAM had already pointed out in 2007 that the same technique doesn't apply to CR or to film. With careful calibration and long exposures a DDA exceeds film's contrast sensitivity, down to wall-thickness changes of about two parts per thousand, while in CR the limit remains the plate's own structure. It's no accident that ASTM E2446-24 also classifies CR systems by best achievable equivalent sensitivity, from 1% for the top class to 1.92% for the lowest.
DR's constraint is geometric. The panel is rigid and fixed in format, and its resolution must meet the maximum SRb that ISO 17636-2 sets for each band of penetrated thickness. In class B that's 0.10 mm between 12 and 40 mm, with stricter values on thin walls. A panel that falls short can compensate within the standard's limits, which in 2022 allow up to three compensation steps, or turn to magnification, which however needs a small-focal-spot tube. How to size the panel to wall thickness is covered in our piece on DR detectors for weld inspection.
The number is easier to grasp at scale. An SRb of 0.10 mm is the image's effective pixel, and the standard defines it as half the measured unsharpness. If a 20 mm weld were as long as a two-meter table, a hundred times larger, the image would be built from one-centimeter tiles. Anything finer than a tile at that scale would shrink to a shade of gray.
Moving off film?
Tell us your joints, wall thicknesses, volumes and where you work: we'll tell you whether CR or DR fits and in which configuration, with a no-obligation test on your own material and a tailored quote within 24 hours.
Email us Message us on WhatsAppCR and DR side by side
| Criterion | CR (imaging plate) | DR (DDA panel) |
|---|---|---|
| Examination practice | ASTM E2033/E2033M-24 | ASTM E2698-26 |
| System classification | ISO 16371-1:2011; manufacturer's ASTM E2446-24 | Manufacturer's characterization, ASTM E2597/E2597M-22 |
| User verification | ASTM E2445/E2445M-20, not an acceptance test | ASTM E2737-23, not an acceptance test |
| Time to decision | Scanner readout after every exposure | A few seconds, part still in position |
| Sensitivity limit | Plate structure | Multi-level calibration, beyond film |
| Geometry | Flexible plate, free formats | Rigid panel, fixed format |
| Environment | Field work and bad weather too | Best with stable temperature and humidity |
| Scatter | Thicker lead screens than with film | Dedicated filtration with scintillator panels |
Read row by row, the table mostly tells you which questions to ask before ordering. The most important one is checked against the standard's tables and on test pieces: the panel has to reach the SRb required by the thinnest wall, or the cycle-time advantage stays on paper.
After acceptance, who keeps the system in check
On installation day both technologies start from a manufacturer's characterization, ASTM E2446-24 for CR and ASTM E2597/E2597M-22 for panels, designed to compare systems from different suppliers. From then on, responsibility passes to whoever uses the system. For CR, ASTM E2445/E2445M-20 describes periodic performance and stability tests on scanner and plates, whose service life depends heavily on handling. For DDAs, ASTM E2737-23 sets a baseline with a dedicated phantom and tracks drift, including image lag and burn-in. Both state that they are not acceptance tests, so a contractual acceptance test has to be written separately into the order, naming the parts and images it will be judged on. ISO standards are moving the same way: the revision of ISO 16371-1, now at draft stage, adds long-term stability of systems to the title.
Two numbers sign the report, along with how it's read
A digital radiograph passes or fails on two quantities, and both are settled before anyone looks at a screen. The first is basic spatial resolution, half the unsharpness measured with the duplex wire IQI, which is the effective pixel whatever pixel pitch the datasheet prints. The second is normalized signal-to-noise ratio. Source, energy, focal spot and distances, the things buyers argue about, reach the report only through those two figures.
The same goes for the part nobody quotes for. ISO 17636-2 notes that computer, software, monitor and viewing conditions matter to the result, even though they aren't its main subject, so it leaves the procedure and the contract to pin them down. Buy the detector, read images on an office screen, and the shop owns hardware capable of class B without the chain that proves it. The archive belongs here too: the DICONDE format of ASTM E2339-21 keeps images readable for years outside the supplier's software. A shop with a legacy film archive can bring it into the same system with a film digitizer.
Cost is read per exposure
The economic comparison between CR and DR is made on full cost per exposure, with investment share, periodic checks, consumables, plate life and operator time, over the years the company uses to depreciate capital equipment. The figures depend so much on volume that a generic value wouldn't help: the method, with a worked case, is in our guide to X-ray system costs and quotation. Here the underlying criterion is enough: CR weighs less up front, and DR gains with every extra exposure. Volume is the variable that flips the answer, so the first figure to pin down is how many exposures a year the system will actually make, split between bay and field.
What to send us for an assessment
To tell you whether CR or DR fits, and in which configuration, we need these data:
- materials, penetrated thicknesses and joint or part types, with diameters and difficult geometries;
- technique standard, required class and the customer's acceptance standard;
- available sources: tubes with voltage and focal spot, or isotopes;
- exposures per day or month, in the bay and in the field;
- current workflow: film, outside lab or CR already in use;
- archiving and reporting needs, including DICONDE format.
You can send them by email to info@dipitech.com or on WhatsApp, with drawings or reference radiographs.
Stripped to the bone, the choice follows the part and the workplace. Where geometry changes and work moves around, CR remains the more flexible route; where joints repeat at a fixed station, DR delivers more, as long as the panel handles the thinnest wall without leaning on compensations. When your inspections sit on one side, or straddle both, the way to decide is a test on your own material, backed by a tailored quote within 24 hours and technical support in Italy. Both technologies are also described, alongside X-ray sources, on our CR and DR digital radiography page.
Frequently asked questions about CR and DR in industrial radiography
What's the difference between CR and DR radiography?
In CR a photostimulable phosphor plate is exposed and then read by a laser scanner; in DR a flat-panel array delivers the image in seconds with no intermediate readout. For welds both fall under ISO 17636-2:2022 and must reach the same sensitivity as film in the required class.
Does CR or DR give better images?
With careful calibration and long exposures DR can beat film on contrast sensitivity, because calibration removes pixel fixed-pattern noise, which isn't possible with plates. CR still reaches the required class if the full system of plate, scanner and settings meets the standard's SRb and signal-to-noise ratio.
Can CR be used in the field?
Yes, and it's one of its strengths: plates bend in cassettes, fit around pipes and irregular shapes and handle mobile work even in bad weather. Scatter shielding needs attention, with thicker lead screens than those used with film on steel.
Which standards govern CR and DR in weld inspection?
The technique is in ISO 17636-2:2022 for both. CR also falls under ISO 16371-1:2011 for system classification and ASTM E2033/E2033M-24, E2446-24 and E2445/E2445M-20; panels under ASTM E2698-26, E2597/E2597M-22 and E2737-23.
When does it make sense to move from CR to DR?
When the same joints come back many times a day at a fixed station and plate readout becomes the bottleneck. First check that the panel reaches the SRb ISO 17636-2 requires on the thinnest wall you inspect, without compensations beyond those allowed.
How much does a CR or DR system cost?
It depends on formats, resolution, number of plates or panels, software and service, so a generic price would be misleading. DIPITECH prepares a tailored quote within 24 hours from wall thicknesses, part types, required class and volumes, and can arrange a no-obligation test on your own material.