3" panoramic?

Date 03-27-2008 12:34 Edited 03-27-2008 12:42

I can see your thinking outside the box, which is a good thing, but I see some concerns in your post. I'll state the first and most obvious one first.

The source cross section/focal size you've quoted implies iridium 192. So I'll go with that assumption for the time being.
D4 film will require somewhere in the neighborhood of 4.5 to 5R to properly darken the film, so for academic purposes, I'll go with the 5R figure.

IR192 outputs 5.9R per hour at 1 foot; you have a 3" tube; you wish to shoot this panaramic; if it's standard size, it should be in the neighborhood of 3.25" but I'll stick to 3" to make it even.

@ 1 foot and 1 curie you'll output 5.9R per hour. @6" it will be 23.6R @3" it will be 94.6R, and @1.5" (where your source would be set for a panaramic) it will output 377.6R per hour or 6.29R per minute. Half value layer of steel is about .5" depending on the steel for Ir192, so you'll have a .5 hvl round about. This will put your shot time somewhere in the range of 1 minute with 1 curie.

At that low a level, you'll have to calc out the "exact" activity of that source, as 1.2ci vs 1, or .8ci vs 1 will have a dramatic effect on shot time, vs say a 10ci source at 12" the difference in .2ci will not be very noticable if noticable at all.
Factoring in the half life of IR192 at approx 74 days, you'll have a very limited window in which your source will be viable for this kind of shot.

From the quality standpoint, you have to remember that source size is over half of your wall thickness and will be shot from a centerline of 1.625" away from the surface of the film assuming intimate contact of part and film. At that distance the difference in diameter of that source will have an effect on your shot, and your UG will vary for the same reason. If I am not mistaken, the standard UG formula does not take into account what you are proposing. It would also have to be remembered that you will have to calc that ug to the surface centerline of the pill it'self at the distances your proposing.

Simply put I don't see this being possible from a quality standpoint or an economic standpoint, at least not with IR192.

Having said all that there is an option of you go with a selenium75 source.
http://www.asnt.org/publications/materialseval/basics/feb99basics/feb99basics.htm

In 2002 I took part in an effort to qualify a mothballed reactor head for service. Some of the original test records could not be found, so the friction welds on the stalks had to be retested. Given the distances between stalks, shooting them with standoff was not a real option. Given that I've sleep many nights since then, I can't recall the exact parameters used on that one, I do recall the answer was selenium75 with shots taken from the ID of the stalk out.
Given that an 80ci Se75 source can be obtained with a .118 cross section/focal size and that our source was special ordered and had a (distance memory so verify for yourself first) .05 cross section at 10ci it worked out for us and the NRC.

.146" will not work, but .05 should. A half life of 74 days will not be economically feasable to maintain, but a hl of 120.4 days would be. 5.9hr/per ci is not feasable either as they are typically sent back long before due to the hl, I doubt You'll find an Ir192 source less than 10ci for that reason (10ci of ir192 would be near impossible to shoot with at those distances due to flashing the film and the super short shot time). Then there is the <=2.8 or so R/h value for Se75. All in all, I believe this is a possible answer for what your intention is. You could special order the source, and with the added half life, keep that source cooking for a year vs 3 months for the ir192. Se75 also works great for CR radiography. That is another option for you if time is your concern.

In summary, what you propose I believe may be possible, but not in the manner initially proposed.
Suggest further research into the matter.

Regards,
Gerald

By kipman

Date 03-31-2008 07:07

Also, the normal small variation in source to film distance that is essentially unavoidable in all cases will really be magnified with a source to film distance that is that small. This will cause great variation in Ug and in density.

I personally don't see any benefit in trying to shoot 3" pipe panoramically. The set up time you would need to try to offset the SFD variation that I mentioned above would likely more than offset any savings in time you gain by only having to take one shot. A 3" weld can be shot very quickly using the contact method. This is the way I would go.
Mankenberg

By CWI555

Date 03-31-2008 14:21

There can in fact be a very modest times saving with proper jigging etc. Having done it myself, with the se75 set up mentioned, it's not a bad way to go. A good portion of that unavoidable magnification is in fact avoidable with Se75 source as mentioned. Ir192 is as you say, not possible, but I believe that was made clear.

By raptor34 (**)

Date 03-31-2008 14:44

I tried this out the other day just to see what it would do and we shot 5 welds in about 3 minutes, so the speed factor of it was there like i thought. but the film quality wasnt what i wanted it to be, i had a good density in the weld but outside of the weld wasnt very good, I used a B iqi and i could see all the wires really good but it stretched out the id pretty bad. se75 is what they are using for the digital rt isnt it? My company doesnt do that yet and i would be interested in finding out more about it. thanks for the help guys.

By CWI555

Date 03-31-2008 23:23

Cr/Digital can use any source. However; Se75 is used due to reduced source cross section which aids in lower UG, as well as due to the difference in energy. You must remember that seeing the wire is not a guarantee of quality in regards to the UG, especially if your wire is film side. I believe you will be pleasantly surprised if you switch over to Se75 and try it again.

By thirdeye (***)

Date 04-01-2008 01:58 Edited 04-01-2008 02:00

Would you mind telling us what type of cassette you used in your experiments? Was it a canvas type or did you use some kind of ready-pack? Wrapping 1/3 of the joint is hard enough, so I was wondering what type of contact you had for a pano wrap.

Just shooting from the hip here, I'm guessing the welds are all the same configuration, like maybe all flange to pipe connections. A jig to center the source tube tip would be easy to rig-up.......what did you use?

My "slide-rule" calculator does not go down enough to enter the variables for this shot, but even taking a wild guess with 6 to 10 curies and using D-3 would put you in the range of 10 seconds. Even a 1 second difference in exposure time would result in a 10% swing in exposure time. Did you notice a density difference during your trials?

~thirdeye~

By raptor34 (**)

Date 04-05-2008 03:28

I used a 14" x 70mm canvas cassette with .005 leads front and .010 leads on back. I had 23 ci of IR-192 with an agfa D4 film and shot it for 4 seconds. as for figuring the shot time i figures for .216 wall and 3.5 inches source to film and divided by 4 to get my shot time since i would be half the distance. The jig i rigged up was from a night cap for a 3 inch pipe with a hole drilled in the middle, the desity all around the weld was really consistant but as you go away from the weld the density got lighter. next to the weld it ranged from a 2.4 to a 2.9 and at the edge of the film it was between a 0.8 to 1.3. I did find one weld that had a defect using contact and shot it to see what it would show and i could see the defect it did blow the image to appear bigger than it really was and also the grinder marks showed (the beads are all gound flush on the inside to illiminate turbulance of the gas passing thru) as for keeping the shot times consistant i use a timex (anybody new to the industry reading this go to walmart and buy you one with the timer you can set, it runs about $30 and is well worth your time and money to do so.) and know that it takes one second to hit the start button and so i set it for 3 seconds and crank in when the timer goes off.

By Bill M

Date 04-07-2008 13:55

Since you asked about the Code, AWS D1.1 lets you do a panoramic shot on 3-1/2" or less OD -

See D1.1, Section 6.18.1.3 for more info