Digital Radiography compared to screen-film and standards

[Ndtmetal]

Hi All,
I was wondering if there are any available standards for digital radiography yet? In thread thread286-141480 someone mentioned that digital RT is currently being reviewed under a proposed ASME Boiler and Pressure Vessel Code case. When is that expected to be ready?

I am working on a quality procedure for Al,stainless steel and 304L welds-the samples will be created by laser welding.
And I'm not sure if I should use digital or not.

Moreover I would like to ask if there is someone who can explain to me the differece between the terms ,digital, computed and numerical radiography because it seems to be a confusion there.

Thank in advance for your responses.

 

[CoryPad]

As far as standards, I would check the most current ones from ASTM International. There are more than 50 that cover radiography.

In general, digital is equal to film, so you should be able to use digital.

The difference between terms are:

digital - acquiring an x-ray pattern using an electronic detector, as opposed to film

computed - this is for volumetric information, as opposed to the areal information from standard radiography. Computed requires a moving source/detector system, as opposed to a positionally-fixed system.

numerical - not sure about this one

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Ndtmetal]

Thanks corypad,
I thought that computed RT was the one that uses phoshor plates instead of digitalizing plates.

What about advantages and disadvatages of each technique. Is it true that digital RT cannot find cracks in chrome welds?

 

[CoryPad]

The advantages of digital are ease of acquisition, storage, and viewing of the radiographs. The disadvantages are really just related to learning about the vendors, products, and techniques for this newer technology.

Computed radiography is much more expensive than standard radiography. The equipment (including the computing power) is much more advanced. The advantage is that you can get a cloud of data for the entire volume of your part rather than only getting a slice as you would from standard radiography. What kind of welds are you working on? I don't think it is likely that you will need to use computed radiography.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Ndtmetal]

Laser welding detecting defects smaller than 4-5 mm

 

[ElderX]

NDTMetal,

There is a dizzing array of products available to the NDT practitioner and choosing the appropriate technolgy for the task at hand can be challenging.

Digital radiography is a generic term that can be applied to all radiographic techniques using computers but is generally meant to encompass radiography using flat panel or linear array detectors CMOS for example. Digital radiography usually produces an image realtime or near real time.

Computed radiography on the other hand is similar to film where radiographic plates are exposed and run through a special reader/processor then displayed on a computer screen.

As far as digital radiography's comparison to film radiography several factors have to be considered in your choice of a digital system.

1. The resolution of the detector in use is one. There are CMOS detectors available that will provide down to approx. 50 microns of resolution while most flat panel detectors are in the range of 125 microns

2. The size of the source will directly affect the geometric unsharpness and hence the apparent sensitivity. With the newer generation microfocus tubes very small focal spots in the range of 10 microns with 8ma and 160KVP are commonly available.

http://www.shieldalloys.com/articles/nl_01.htm

3. Because the radiation requirements to produce an image using digital detectors is usually much less than those for film radiographic images for a given thickness and energy level the time to produce the image is shorter and processing time is eliminated.

4. Because the object being radiographed can often be rotated in real time and many times just the re-orientation of the object into a more favorable plane with the radiation beam and detector can reveal flaws that are not seen with a couple of shots using film.

I hope I have answered some of your questions. My experience with digital radiography since I started in 2000 has been good. Is it the answer to all the problems? No. One must always consider all the options and choose from the best available.

How can you know? I would say get the folks that sell the equipment like GE, Envision Products and others to take some of your products and provide images, then you have a better idea how it will work for your particular application.

ElderX

 

[Ndtmetal]

I'm already having GE to test computed radiography on the 29th of May.
the question now is when will I have better results, with the phosphor plates or by usings screen-film RT but with selenium 75?