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Technical Discussions
Ken
Senior Level III
USA, Joined Jan 2000, 14

Ken

Senior Level III
USA,
Joined Jan 2000
14
20:40 Mar-10-2010
Digital RT

I have been asked to review the procedures on a digital system for one of my clients and let them know if anything caused me any concern. I know next to nothing about a digital radiography but one of the concerns was that my client could see the essiental wire used in the system but it as well as the weld image appeared "fuzzy". This is using the API 1104 acceptance criteria so not much help there. Are there any things I should look for? There is no specific criteria mentioned in the code or in the procedure about the monitor. Is this something that should be reviewed? Any help would be greatly appreciated

    
 
 
Jon Wallis
NDT Inspector, -
Netherlands, Joined Feb 2010, 626

Jon Wallis

NDT Inspector, -
Netherlands,
Joined Feb 2010
626
10:18 Mar-11-2010
Re: Digital RT
In Reply to Ken at 20:40 Mar-10-2010 (Opening).

I am assuming because you talk about API 1104, which is a pipework / pipeline norm, that the objects to be examined are welds. Although manufacturing companies of digital sytems are trying to get systems up to speed with regard to image quality (unless things have changed within the last year) they haven't really managed it yet. A secondary problem is the imaging plates. They need have to 'wrap' around all ≥4" dia welds.

Image quality is measured, according to API 1104 by being able to clearly see the requisite wire of the proper IQI. If you cannot define clearly the essential wire, the method doesn't comply with the Norm. I realise that we are now talking in 'shades of grey' and there will always be parties that will try and argue an opposite view, that said, interpretation of radiographs will produce a similar result (show a radiograph to 10 different interpreters and you'll get 10 different interpretations...).

Looking at a procedure written for on-stream radiography, a monitor with a resolution of 2 Megapixels or better is required. Weld examination would, in my opinion, have to meet this requirement as a minimum.

You say that the image seems fuzzy - suggesting poor definition (compared to film). How did you view the image, was it a simple paper printout or on a monitor? I suggest you contact the ndt company that produced the image, if possible, and discuss these issues with them.

Hope this helps.

    
 
 
Ishbel
Consultant, Engineering Consultant - NDT
Subsea 7, Norway, Joined Nov 1998, 11

Ishbel

Consultant, Engineering Consultant - NDT
Subsea 7,
Norway,
Joined Nov 1998
11
13:18 Mar-16-2010
Re: Digital RT
In Reply to Jon Wallis at 10:18 Mar-11-2010 .

I think that you might find that this refers to digital radiography using linear detectors instead of phosphorus plates. We used this on a project recently with very good results, i.e. atained required sensitivites with scan rates of about 4 minutes for an 18" clad pipe.

The system we used had 2 linear detectors at 180 degrees from each other, which rotated around the pipe, with the X-ray source position internally (panoramic technique).

Both Shaw Pipelines and Applus RTD have systems, and I am sure that you will be able to find details on their websites.

    
 
 
John O'Brien
Consultant, -
Chevron ETC , USA, Joined Jan 2000, 278

John O'Brien

Consultant, -
Chevron ETC ,
USA,
Joined Jan 2000
278
17:15 Mar-20-2010
Re: Digital RT
In Reply to Ken at 20:40 Mar-10-2010 (Opening).

You are correct API 1104 is weak on defining the requirements for non film imaging methods. There are some generic clauses but the lack detail. However the overiding feature of API 1104 is that they need to establish a procedure and then demonstarte it produces images acceptable to Code and COMPANY. The actual imaging media will play a big role as pointed out by Ishbel. Linear CCD or other type detectors are appearing to be more suitable tha the Phosphor Imaging plate approach but since you don't idnetify which technology is being applied its hard to be specific.
If you feel the images lack the required clarity you should use the 'masking of areas of interest' sentence and request they prove resolution. Look in ASME Section V there are procedures there for monitor resolution, scanning pairs etc. Europe also has some draft standards out under working code TC138 I believe.

    
 
 

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