RT Source Size?
RT Source Size?
(OP)
Does anyone know what aproximate dimensions would be for a 60 curie Cobalt 60 source? I was doing some unsharpness calcs using our Iridium size for our heavier wall, and we're teetering on the ASME limits with .068. I was under the impression that the source size for Co-60 was a bit larger, but can't get any actual values as the site hasn't picked a sub for their RT yet.





RE: RT Source Size?
http://www.testima.eu/prilohy/143/infonormy.pdf
RE: RT Source Size?
The size numbers I remember using for anything 100 or under Curies was 0.060" x 0.060".
http:
RE: RT Source Size?
RE: RT Source Size?
Your best bet is to check with your isotope supplier. We use QSA Global, nee. Amersham, nee. Tech-ops. The size of our Co-60 (purchased as 100 Ci) is:
.150 dia
.175 length
.200 maximum (diagonal)
JR97
RE: RT Source Size?
Assuming a 60 Curie 2220 GBq Cobalt60 source is cylindrically-shaped (either a monolithic pellet or several wafers pushed together) then one possible way of minimising geometric unsharpness of these higher-activity, larger size isotopes is to ensure that the pig-tail guide tube is facing the weld end-on (rather than transverse) so that the maximum effective source dimension will be the pill diameter.
I am not sure how this will affect radiation output, but at a guess, as each pill is supposedly omni-radiating I would hazard a guess at 'not signifciantly'.
I would like to hear other peoples' knowledge or views.
Nigel Armstrong
Lloyds Register
Independent Verification Body Surveyor
RE: RT Source Size?
I too am curious as to just how much the source orientation would affect GUS. Unfortunately, we're very borderline right now, and the size of our main steam (4.094" wall, 22.5" dia) will be what dictates whether or not we need to perform UT/AUT on site. Which then means getting a P91 dropoff from the fab shop, machining a test block, etc...
That 3mm/.118" value has come up for me in a few different searches now, but who knows at this point. As little difference as .004 in the spec will bump us out.
RE: RT Source Size?
I believe that is the actual size of the pill/case and not the size of the pellet. The pill varies from camera to camera. A pellet of Co60 that size would be a whopper.
The only time pellet size didn't matter was when we used fish pole radiography.
Here is a very good site on whys and wherefore's of Gamma Radiography.
http://w
RE: RT Source Size?
According to its literature the Nordion G3 capsule (sealed source) can take Co60 up to 80 Curie (2.96 TBq) and its OD is 5.1mm (0,204 in), length 16.2mm.(0,64"). The Co60 discs have a diameter between 1mm (0,040) and 3mm (0,120) and a height of 1mm. Various diameters will have various activities, but unfortunately that info is not to hand. Stacking the discs will give greater activity. The sketch shows the capsule loaded with 6 discs and stoppered. If that is the maximum number of discs it can take (I dont know that) then fthat could imply each wafer has an output of about 16 curie and even for 60 Curie yourlength would still be 5mm. Now that is far too big for any reasonable unsharpness level if used transverse, giving an effective focal spot size of almost 6 mm (0,240").
After consideration I think that AUT with TOFD would be the way to go if you really wish to detect any defects!!! Good luck!
Nigel Armstrong
Lloyds Register
Independent Verification Body Surveyor
RE: RT Source Size?
RE: RT Source Size?
The dimensions I quoted (.150 x .200) are the pellet size. The dimensions are listed as a specific data entry on the source decay table provided with the source.
Mr168,
What ASME Code are you using? ASME Pressure Vessel Code Sections I and VIII allow larger than specified Ug provided required wire or hole is still visible.
I am running the Ug formula from Section V, greater than 4" thickness the allowable Ug is .07". You will meet that even using the .200 diagonal measurement and having the source at center of pipe.
RE: RT Source Size?
RE: RT Source Size?
ASME Ug values are by definition Lowest Common Denominator - the very minimum acceptable radiographic quality, suitable for detection of workmanship slag and porosity defects perhaps, but under these conditions not lack of fusion or -hush! - cracks. Expected flaw type depends heavily on the welding process. If planar defects are a possibility then a Co60 exposure with an Ug of 0,068 will render any captured image of a planar flaw practically undetectable to the ordinary human eye due to the low contrast across the image.
My view is that for a reaonable POD of planar defects then properly controlled phased array/TOFD/AUT is the way to go.
Nigel Armstrong
Lloyds Register
Independent Verification Body Surveyor
RE: RT Source Size?
RE: RT Source Size?
ASME B31.1 paragraph 136.4.5 specifically allows Ug of up to 0.07 inches. Even assuming 0.200 diagonal measurement for the Co60 source, you meet your specification with a panaramic exposure. IMHO, RT of the joint would meet all specification requirements (assuming source size of 0.200" or less).
I have to respecifully disagree with NDEGUY, the imposed specification is written to allow radiographs with Ug of up to .07. Therefore, by definition, adequate radiographs can be made with that unsharpness and there is no reason to consider alternative methods. If the specification imposed contained a more stringent requirement, then alternatives would be necessary. Bottom line, just because there may be a potentially better inspection out there is not justification to use it unless contractually imposed and compensated by the customer.
RE: RT Source Size?
My Ug calc for a panoramic exposure was based on 22"OD, 4,094"wt, 14,312"ID and 0,2" effective source size giving Ug = 0,11"
Exchanging 22"OD for 22"ID (30"OD)gives panoramic Ug = 0,074".
If correct then both are outwith Code requirements and both giving poor defect image definition and detection.
I agreee with JR97 that the legal obligation is to meet the contract and specified Code requirements and nothing else. I believe that the customer is entitled to receive what they require and similarly they should pay for that. I also believe that in high pressure safety situations each professional should be enabled to make his/her engineering judgement input to the overall quality of the product. Of course I am aware that this is an ideal and the engineering industry does not run on ideals, but if a better inspection is available then the customer should at least be given the option to use it.
Rant over, good luck with the work Mr168, might even be completed before this thread ends!!!
Nigel Armstrong
Lloyds Register
Independent Verification Body Surveyor
RE: RT Source Size?
Given the difference in opinion of what the source size is going to be, looks like we we're just going to have to wait until they pick their sub and find out the actual size before making the call.