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1956 views
09:53 Jan-22-2009
john latham
x-ray speed

Hello,

We are a steel construction company in Kenya
We have been using a gamma source for x-rays for a while
We have a job that requires exposing 450mm films through 40mm steel plate
given a machine such as below how long will this take?:

Philips MG161L 160kv 10mA Mobil Constant Potential x-ray

Many thanks
John

 
10:51 Jan-22-2009

Nigel Armstrong

Engineering, - Specialist services
United Kingdom,
Joined Oct 2000
1094
Re: x-ray speed In Reply to john latham at 09:53 Jan-22-2009 (Opening).

Hello John

The answer depends on several factors such as radiation output from the tube, proposed shot set-up (FFD), machine duty cycle, required minimum film density. Do you know any of these, John? And will your exposure be in a fully-shielded enclosure or out on site? Is it a weld in the plate you are examining, and what indications are you looking for? Any possibility of using ultrasonics?

In my opinion your proposed equipment is not quite up to the job. 40 mm thick Fe plate is right at the very limit of "penetrability" for a 160kV CP X-ray set. To get anywhere near a density of say 2.5 will require a long exposure time - if you get any penetration at all. If you could get your hands on an 200kV CP set then the exposure would be practical.

 
12:15 Jan-22-2009
TJ
Re: x-ray speed In Reply to john latham at 09:53 Jan-22-2009 (Opening).

It would be a mistake to obtain a 160 kV tube for use on 1.5" steel plate. The energy of the X-rays at that point are insufficient to penetrate that much material in any practical amount of time.

TJ

 
17:33 Jan-22-2009

Michel Couture

NDT Inspector,
consultant,
Canada,
Joined Sep 2006
806
Re: x-ray speed In Reply to TJ at 12:15 Jan-22-2009 .

Hi John,

I totally concur with Nigel an TJ, but would like to add this comment. When doing radiography with a tube (xray) the first thing one should do is an Exposure Chart using Logarithmic Graph Paper. This graph will be done for a Specifice Density, KV, mA and FFD.
On the graph's vertical, you will have your mA. S. (milliAmp x Seconds) and the horizontal will be your material thickness.

For example, you may choose a Density of 2.5, FFD of 36" and 10 mA and your film. Your first curve maybe at 100 kV. So using a Step Wedge of the material and thickness range required, you make an exposure of lest say 60 seconds, than another film with an exposure of 2 minutes and another of 4 minutes and than 8 minutes. Process your films and find on your different exposure where the density is 2.5. Plot the thickness against the mA. S. for your 4 exposures. Repeat this process adding 20kV for the next set of exposure throught the range that you want to use your tube.

This will tell you what your tube is capable of doing. FYI, when I was in the Air Force, we use to do lots of X-Ray and with our parameters (FFD 36", Density 2.0, 4 mA with Automatic Development of Kodak AA) a 3/8" of Steel was about 240 mAS at 120kV and 2.75" was 1920 mAS at 200kV.

I hope this will be of help to you.
Cheerio's

 
05:25 Jan-23-2009
Scott Cargill
Re: x-ray speed In Reply to john latham at 09:53 Jan-22-2009 (Opening).

I would strongly suggest obtaining a tube capable of at least 200 kv, perferably 300 kv.

A shot using the 160L at that thickness range is really pushing the outer limits, you would be running the system beyond its practical limits.

Typically the rule of thumb is to not exceed 80% of a systems duty cycle and potential. In your case 140 kv, 8 ma, and knowing that system, a 5 min shot at a time with at least 5 minutes to cool down.

 


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