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1930 views
09:41 Oct-15-2009

anjafo

NDT Inspector
Norway,
Joined Aug 2009
204
5" xxs centre shot gamma

Hi,
Trying to work out if I can do centre shot according to ASME V.

My schedule list says its 141,3mm OD x 19,05mmWT.

Source size is 2.00x1.12mm

Its the Ug that seems to be just over when using source size as the max stated on decay chart of 2mm.


    
 
21:21 Oct-18-2009

Phil

NDT Inspector, Radiation Safety
BINDT, MIAQP,
United Kingdom,
Joined Mar 2009
151
Re: 5" xxs centre shot gamma In Reply to anjafo at 09:41 Oct-15-2009 (Opening).

Hi Anjafo,

I would not like to see the film as I figure your Ug would be way out. Plus I would expect you to be using the slowest film you had. I have in the past had to shoot 3" WQT's as per Client instructions Panoramic not a nice film but was to Client instruction. If it is a Client instruction you point out the problem then shoot the film.
Good luck


    
 
12:40 Oct-19-2009

anjafo

NDT Inspector
Norway,
Joined Aug 2009
204
Re: 5" xxs centre shot gamma In Reply to Phil at 21:21 Oct-18-2009 .

Thanks Phil,

The Ug is not way out (according to spec) using max source size, I believe it is just over. Using the min source size it is in spec. I got 0,53 Ug for max source size.

1 question is does it state anywhere what is actual source dimension to be used when supplier states 2mm x 1.2mm (if we average size it gives us 1.6 which is still with in limits)?

Films are good and sensitivity is achieved although we have had problem centre shooting 4" heavier wall (within spec) before.

Shooting DWSI there is almost 40mm of steel to get through so longer shooting time, more shots (more film) although we did not take a test to see which one "looked better".

I think its more about what may be missed than "looks", especially on the root as I think thats where ther worst case of Ug will be?


    
 
14:03 Oct-19-2009

Roger Duwe

NDT Inspector, API-510, 570, 653
MISTRAS,
USA,
Joined Jan 2009
148
Re: 5" xxs centre shot gamma In Reply to anjafo at 12:40 Oct-19-2009 .

A 2 x 1.2 source has a diagonal of 2.3. The source size is the largest inscribed dimension, which on a cylinderical RT gamma source is the diagonal. That is why Phil stated that "Ug would be way out".

Since the IQI would be film-side, you will have good "looking" film, with very poor sensitivity of the root area, and with the root indications considerably distorted and magnifyed.


    
 
14:09 Oct-19-2009

Phil

NDT Inspector, Radiation Safety
BINDT, MIAQP,
United Kingdom,
Joined Mar 2009
151
Re: 5" xxs centre shot gamma In Reply to anjafo at 12:40 Oct-19-2009 .

Hi Anjafo,

I expect you would be using a source, as per your Radiographic Procedure, which is Client Approved to give you acceptable films in normal Radiography, and as you say DWSI, will bring in longer exposures, you could well have taken the best possible option, by doing it SWSI, and as you say it will be what is missed, but you have to account for the Inspector, and how he views the film.

Regards,


    
 
15:11 Oct-19-2009

anjafo

NDT Inspector
Norway,
Joined Aug 2009
204
Re: 5" xxs centre shot gamma In Reply to Phil at 14:09 Oct-19-2009 .

Thanks guys. I think best to go with DWSI.

Roger: Thanks for the source size explanation.

It would be good to have a calibration block like in UT where you have different depths/sizes of defects for sensitivity control but with the variety in RT its not so easy to obtain. A lot of shots may look good but you dont know whats being missed!


    
 
15:56 Oct-19-2009

Phil

NDT Inspector, Radiation Safety
BINDT, MIAQP,
United Kingdom,
Joined Mar 2009
151
Re: 5" xxs centre shot gamma In Reply to anjafo at 15:11 Oct-19-2009 .

Hi Anjafo,

Go with what ever you think is best taking in safety and exposure.

Regards,


    
 
23:03 Oct-19-2009

Roger Duwe

NDT Inspector, API-510, 570, 653
MISTRAS,
USA,
Joined Jan 2009
148
Re: 5" xxs centre shot gamma In Reply to Phil at 15:56 Oct-19-2009 .

anjafo;
You might try a mock-up shot. Try to find a weld that is within reaching distance of the end of the pipe, like a short stub onto a flange or elbow. [If nothing else, RT a blank piece of pipe]

Place the proper IQI packet on the inside of the pipe - source side- tight against the pipe wall and see if you can get proper sensitivity. Ug can be ignored [for cause] if proper sensitivity can be proven.

RT of the actual material is always better than a calibration block, and is usually faster and easier. "When in doubt, ask the parts"


    
 
23:23 Oct-19-2009

anjafo

NDT Inspector
Norway,
Joined Aug 2009
204
Re: 5" xxs centre shot gamma In Reply to Roger Duwe at 23:03 Oct-19-2009 .

Eaxtly what do you mean "ignored (for cause)"?

Thats allowed to asme v?

I doubt we will get wire required but will let you know.


    
 
00:21 Oct-20-2009

Juan Amado

Engineering, Inspection
Arco Industrial, S.A.,
Panama,
Joined Nov 2001
44
Re: 5" xxs centre shot gamma In Reply to anjafo at 23:23 Oct-19-2009 .

This is an interesting discussion, and one in which I feel we can also gain valuable insight into how RT is practiced around the world.
1. I agree with the statement that the Ug is “far off” to begin with, because the focal spot dimension to be used is the largest inscribed dimension of the source. In this case, a source which is essentially a cylinder made up of wafers or discs that measures 2.0mm in one dimension and 1.12mm in the other, will have a maximum inscribed dimension (the diagonal inside the cylinder) of 2.3mm. Unless you have certainty of how this cylinder is going to be oriented when facing the object and projecting onto the film, which we seldom do, it is important to use the worst case scenario which would be 2.3mm. Using this number would yield a Ug = 0.849mm
2. I would like to add that according to ASME Section V, Article 2, paragraph T-221.1 states that RT must be performed in accordance with a written procedure and lists the essential parameters which must be included in that procedure. Paragraph T221.2 then goes on to say that demonstration of the density and IQI image requirements shall be considered satisfactory evidence of compliance with the procedure.
3. Although Section V, Article 2, paragraph T-274.2 sets Ug limitations (namely 0.51 if working in mm), other sections of the code take exception to this, for example, Section I (Power Piping), paragraph PW-51, which states that the requirements of T-274 are to be used as a guide but not for the rejection of radiographs unless the geometrical unsharpness exceeds 1.8 mm. So clearly the intent of the code is that you comply with density and IQI image, with prevalence to Ug. Based on this I would contradict myself and tell you that the Ug was not “way off” after all, IF you can achieve both, good density, and the required IQI level.
4. The best advice was already given in this thread in succinct terms, “when in doubt, ask the part”. If you do a couple of test shots and qualify your procedure you’ll know where you stand.

I hope this helps, and thank all contributors for the healthy discussion.
Best regards,
Juan Amado


    
 


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