Radiograhy on small pipe

By - Date 02-07-2004 04:29

The contact method can also be used successfully in many cases on thinner small bore piping - keep in mind your Ug limitations. You may have to make your own cassettes and cut film accordingly for this.

For ellipticals, you'll find a relationship of 7:2 works well (SFD of 7 times the pipe OD and 2 times the diameter offset from the plane of the weld). Remember also the superimposed technique if you have limitations in offsetting the source or if you're on small bore XXS stuff.

I've never done these with an x-ray tube. If you're using a gamma ray source, the only limitation on what you can do is imposed by your own creativity. You should be able to develop a source positioning jig for most any application.

I recall way back when, for instance, making a jig that used the force of gravity on its own weight to lock it in place against the pipe that was being shot, and coupling this with an extra long source tube. This got the source to where I needed it to be.

Good luck.
Mankenberg

By thcqci

Date 02-09-2004 12:32

In my opinion, your assessment of the technique for the 4" pipe is correct.

Assuming you have access to the inside of the 2' pipe, I used to use a spring loaded tube (such as an old spring light pole or pogo stick) on the inside of a pipe or tank. Alternately, for only 2' diameter, you could wedge a 2x4 or pipe cut to inside diameter length in that short distance. Place slightly above or below the weld in interest, whichever is more convienient to placing the source. Duct tape (wonderful stuff) the source tube to the center of the tank diameter so it points up or down, to the center of the tank in line with the weld. I assume 12" SFD is sufficient for thickness of pipe. Film goes on outside of tank.

If you do not have access to inside, you will have to shoot from the outside, through 2 walls. Again, film on outside with source 180° around pipe. I assume SFD will be adequate for 2' diameter to wall thickness ratio.

Get technique right at ground level then shoot up in the air. I would assume whoever you hire to perform RT will know several tricks to RTing in awkwards positions.

Good luck!

By cawelder (**)

Date 02-10-2004 22:56

I would use contact. Its only 1 more shot, and a whole lot easier. Use a rubber strap to hold the film and the source tube to the pipe. Lay the pipe out at 0, 90, 180, and 270. Shoot 3 shots. You need a low curie source. I did some 3" sch 40 last week with a 25 curie source. The shot times were only about 8 to 10 seconds. With this you can use a slower speed film, it makes your work look alot better.

Hope this helps
Chuck

By BankerQC (*)

Date 02-12-2004 15:58

Hello all , In answering your ?'s there are a couple of points that appear to have been missed so I'll add my 2 cents wort....
1.) What code is being used ? that should provide some guidence.
2.) As I recall , the general rule of thumb is that pipe with an OD less than 3.5" must be examined using either a superimposed technique or an eliptical technique which is usally left to the descretion of the radiographer. The primary governing factor is the calculated geometric unsharpness factor or Ug the formula for which I wont go into here.
3.) As far as being up in the air etc. ???..... welcome to the world of field RT ! What worked best for me was to get a set of vise grip pliers ( I liked the kinds with the specialized jaws) and either clamp ( small hose clamps) or weld a piece of all-thread or rod to the handle. This allows you to clamp the "jig" to the pipe in a variety of positions, and the adjustable jaws make it easy to adapt to differing pipe sizes and configurations. Your colimator can be attached to the rod at the proper distance from the subject in several ways such as a set of mini vise grips or creative use of good 'ole duk Tape.

Hope this helps and I didnt mis-remember too much as I have not shot any pipe in a couple of years.

Banker QC

P.S. In some situations you can even shoot multiple welds simultanously If you give it some thought and get creative. Have Fun !

By Mark31

Date 02-16-2004 02:40

You all gave great answers and I'll be looking for some vise grips tomorrrow at the local hardware store thanks Bankerqc...

By Shane Feder (****)

Date 02-17-2004 00:43

Mark31,
As thcqci has mentioned, whoever you hire to do your RT will probably have a few tricks up their sleeve as they are continuously confronted with new and more difficult things to "shoot".
When using gamma on smallbore piping we used the elliptical vice-grip method described by BankerQC.The butt was set up using a JLG for access and the bomb/camera was either hooked on to the pipe adjacent to the weld or it was suspended by a crane to allow you to travel up and down in the JLG.
On butts in the 5G position our two shots were aimed at a point 45° either side of bottom centre which enabled us to "wind out" from directly underneath the pipe with the collimator aiming the radiation in the upwards direction.
Good luck with your shots,
Regards,
Shane Feder