2% radiographic quality level & pennies

Date 11-27-2008 11:57

Mike,

I think I see where you are headed.....but put me on track if I'm not looking at this right. You are correct in that the thickness of the pene selected for a 2% quality level has a thickness of 2% of the part under examination. And I think that most of us will agree that if you can detect that change on a radiograph, (say for example along the edges of the pene or in the area of the hole) you have met that portion of the required quality level.

But now, the second term used in the expressed quality level comes into play. If the expression is 2-2T, one must display the outline of the 2T hole in a pene which is 2% of the thickness of the part under examination. Showing only an edge without the specified hole would not satisfy a 2-2T requirement.

Happy Thanksgiving

~thirdeye~

By michael kniolek (***)

Date 11-28-2008 14:19

well.... i guess i see it like this
if you use the 2-2t hole and can see it you have just met the 2% (regardless of what penny was specified)

By thirdeye (***)

Date 11-28-2008 20:56

Michael,

Maybe I'm reading too much into both of you guy's posts.....Let's say the specified pene is a 12. We know that the thickness of the pene is 0.0125 (inches) and that if used when radiographing 0.625 (inch) thick material the pene represents 2% of the material thickness. (And granted, a particular Code chart may give you a little leeway here, like a material thickness range of 0.500 to 0.625) Anyway, using this example, if you can distinguish the 2T hole on the radiograph, you have now achieved a 2-2T quality level. It's pretty much a given that if you can see the 2T hole, seeing the edges of the pene should be no problem.

I'm not sure what you meant about "regardless of what pene was specified", but keeping the same 0.625 material from the example above.....if a 7 pene was selected instead of the 12 and the 2T hole was visible, you would have greater than 2% sensitivity, something like 1.2-2T quality level. Likewise if a 20 pene was selected the best you could prove would be 4% sensitivity, although you should have no problems having a 4-1T quality level.

~thirdeye~

By Mikeqc1 (****)

Date 12-01-2008 16:52

So, if shooting a .625 thk plate , the pene thickness would be .0125 that is 2% of the plate thickness if the edge of the pene is visible then the shot can pick up the 2% change in subject thickness, correct?
And if the plate is 1" thick a .020 pene is used. If the edge of the pene is visible then the shot can pick up the 2% change in subject thickness on this plate.

ASME SE 94 it is given as
6.2:The quality level usually required for radiography is 2%

The above scenarios both meet the 2% quality level correct?

Now the holes in the pene....... visibility of the required hole in the pene on the film is permanent evidence that the technique was sufficient to produce adequate definition.

Is that correct?

Now the reason im asking this is because someone had asked why se 94 called out 2% and ASME Section V states T 276.2: The designated hole IQI or essential wire
shall be as specified in Table T-276.
In that table are a number of Peneies for each thickness of plate ....
He was unclear as to the relation between them and felt there was a contradiction.
My question is if I use the proper pene for the thickness im shooting and I see the edge of the pene that proves my 2% RQL.
THERE IS NO CONTRADICTION RIGHT?
MDK

By hogan

Date 12-01-2008 19:41

Sound like your getting it. The pen is 2% of thickness (and I believe you are required to see 3 sides, But it has been a while). The 1T is 2% of thickness. The 2T is 4% of thickness. I'm not positive about the 4T, but I think it is 8%

By Mikeqc1 (****)

Date 12-01-2008 20:07

so in short if i have a .625 plate and i use a .0125 shim (12) and i can see the 2T hole i have 2% RQL.
But if i can see 1t hole does that change the 2% or.......would i need a .0075 / .005 shim to get a 1% RQL.
MDK

By thirdeye (***)

Date 12-01-2008 20:14

Hogan,

The "T" refers to the diameter of the hole. 2T is a hole whose diameter is twice the thickness of the pene. 4T hole would have a diameter of 4 times the thickness of the pene.

By hogan

Date 12-01-2008 20:58

I believe that is in relation to the thickness of the pen, but I could be wrong. I seem to remember (I don't have the code handy) that the 1T is equal to the thickness of the pen. The 2T is equal to 2x the thickness of the penn (or 4%).

By thirdeye (***)

Date 12-01-2008 20:10

Mike,

I hope the examples we are using are not getting in the way of the intentions of the Code. In the examples, we are talking about an actual 2% of a given material thickness, and a pene that represents the 2%. Looking at Table T-276 for the .625 thickness we used in the example, it is calling out a 20S or 17F pene, and listing the essential hole as the 2T on each one. If a Code allows for the use of a specific pene in the given material thickness range, that is the proper one when using that Code.

The ability to see the required hole is mandatory. I can't tell you the number of times I have seen an edge, but can't see the hole. This happens often on small diameter pipe when the shim and pene are not contoured to the pipe. It can also happen if the alignment of the radiation beam is off a few degrees, which actually causes the hole to close.

As far as the pene choices in T-276 for each thickness range, one would be for film side placement, the other for source side placement.

~thirdeye~

By Mikeqc1 (****)

Date 12-01-2008 20:30

I think what im hung up on is the 1t hole 2t hole and 4t hole.....
for example
i have a pene i see the "3 sides"...........dose it matter what hole is visible in achieving 2% RQL(I KNOW I NEED TO SEE THE HOLE CALLED OUT IN THE SPEC OR CODE)

My first shot....3 sides of the pene and hole 1T is visible, and my second shot 3 sides of the same pene and hole 2T is visible.
Do the above shots have different RQL? or does the shot with the 1T hole just have better definition.
Ill get this.........................................
MDK

By thirdeye (***)

Date 12-02-2008 03:00 Edited 12-02-2008 03:11

I think what im hung up on is the 1t hole 2t hole and 4t hole.....
for example i have a pene i see the "3 sides"...........dose it matter what hole is visible in achieving 2% RQL(I KNOW I NEED TO SEE THE HOLE CALLED OUT IN THE SPEC OR CODE)

It does not matter which hole, or even if you can't see any hole.....if you can see the edge(s) you have achieved 2% sensitivity.

My first shot....3 sides of the pene and hole 1T is visible, and my second shot 3 sides of the same pene and hole 2T is visible.
Do the above shots have different RQL? or does the shot with the 1T hole just have better definition.

You still have 2% sensitivity on all shots, one has 1T resolution (2-1T quality level) and the other has 2T resolution (2-2T quality level)

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Mike,

Hung up is a good term to use here because in effect, we are hung up on terms.....so, staying with our example(s) where we have been talking about 2% sensitivity....... Now chew on this, and hopefully this will make sense, if not I always enjoy these type of discussions, so we'll keep at it.

Various degrees of image quality can be measured by using a hole type pene. Sensitivity is determined when the pene selected is a percentage of the material thickness being examined. If you can distinguish the difference in density, such as along one edge or more you have proved sensitivity. Likewise if you can also disguinish that same density difference around the edge of a hole, a square, a notch or a triangle shape cut out of the pene you have also proved sensitivity. In our example, this would prove 2% sensitivity.

Resolution is determined by the smallest hole size visible on the pene under examination. (now the hole comes into play) Resolution is measured in terms of 1T, 2T or 4T. 1T represents a hole diameter equal to the thickness of the pene. 2T is a hole 2 times the thickness of the pene, and so on.

Image quality level or quality level are terms where both sensitivity and resolution are taken into consideration. Image quality levels are expressed as 1-1T, 1-2T, 2-1T, 2-2T and so on.

A Code of specification will state the image quality level that is required. This means both sensitivity and resolution must be achieved. Here are a couple of charts that show equivalent sensitivity levels when some of the variables change.

~thirdeye~

By michael kniolek (***)

Date 12-03-2008 21:04

thank you, your input has helped.
MDK