Non-destructive testing methods are special processes?

armani

Involved In Discussions
#1
I read on BINDT (British Institute of Non-Destructive Testing) site that NADCAP consider non-destructive testing methods (ultrasonic, coating thickness measurement etc.) as special processes.

NADCAP

Here is the quote:
"A special process is a QA term which refers to any process where the results of the process cannot be easily verified after completion of the process. Examples of special processes are: Non-Destructive Testing; Materials Testing; Heat Treatment; Coatings. The results of a special process are highly dependent on the control of the process and/or the skill of the operator."

I cannot fit these methods into special process definition - anyone can help?
 
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dsanabria

Quite Involved in Discussions
#2
re: Non-distructive testing methods are special processes?

Not sure what is it that you don't get so let's try this example.

Two pieces are welded but you need to know if the joints are good - so you include a "Special Process" - in this case - Non Destructive Testing - i.e. X-RAY to verify that the welds meet requirements.

Thus - welding is the action and X-Ray is the Special Process.
 

armani

Involved In Discussions
#3
Re: Non-distructive testing methods are special processes?

Not sure what is it that you don't get so let's try this example.

Two pieces are welded but you need to know if the joints are good - so you include a "Special Process" - in this case - Non Destructive Testing - i.e. X-RAY to verify that the welds meet requirements.

Thus - welding is the action and X-Ray is the Special Process.
Welding is a special process by definition....why X-Ray??
 

ScottK

Not out of the crisis
Staff member
Super Moderator
#4
Re: Non-distructive testing methods are special processes?

Welding is a special process by definition....why X-Ray??
The way I see it is that Welding is a special process, as you say, by definition because the only way to test a weld is destructively.
So you might use X-ray as verification method.
But you need to validate that verification method works - thus making that a special process in and of itself.
 

Ninja

Looking for Reality
Staff member
Moderator
#6
Re: Non-distructive testing methods are special processes?

A curiosity, stemming mostly from my ignorance on this topic...

So measuring (testing) the length of a machined part is a "special process"?
- Measuring color?
- Measuring brightness?
- Measuring weight on a balance? Diameter? Height?
- Measuring surface finish of a polished surface?
- Index of refraction?
- All Visual inspection?
- Measuring the distance between electrodes?
- Measuring electrical conductivity/resistance?

All of these are non destructive tests, as are many, many others...:read:
 

Sidney Vianna

Post Responsibly
Staff member
Admin
#7
If you do a Cove search for the words "special process" in the title of the thread, you will find numerous threads where this has been discussed.
 

dsanabria

Quite Involved in Discussions
#9
Re: Non-distructive testing methods are special processes?

Welding is a special process by definition....why X-Ray??
X-Ray falls into the NDT (non Destructive Test).

X ray is able to detect is there are any imperfections in the weld or around the weld without destruction or taking the pieces apart.

Due to the fact that X-Ray is very intrigue - specialist are needed to read the results of the X-Ray - thus "Special Process.

Note: X-Ray is not the only method that can be used to detect imperfection it is only one of the many ways.

To bring simplicity - it's like going to a hospital to determine where the discomfort is at - X-Ray is one of the methods used for that process.

Hope this answer your question as to why...
 

ScottK

Not out of the crisis
Staff member
Super Moderator
#10
Re: Non-distructive testing methods are special processes?

A curiosity, stemming mostly from my ignorance on this topic...

So measuring (testing) the length of a machined part is a "special process"?
- Measuring color?
- Measuring brightness?
- Measuring weight on a balance? Diameter? Height?
- Measuring surface finish of a polished surface?
- Index of refraction?
- All Visual inspection?
- Measuring the distance between electrodes?
- Measuring electrical conductivity/resistance?

All of these are non destructive tests, as are many, many others...:read:
"Non-Destructive Testing" as we're talking about here is very specific to "Special Processes"... A "Special Process" is something that can't really be checked conventionally so NDT is used to look at characteristics that can show if the part will fail... like using X-rays for welding... the x-rays isn't testing the weld strength - it's looking for cracks that can correlate to a weak weld...

So in your examples pretty much all of them can be measured directly without destroying the part, so they are not the results of a "special process"

dig?

The closest I can see in your list is surface finish - in my new job we have some parts where conventional surface finish testing would scratch the part to make it unusable so that's a destructive test for us... we're looking into non-contact profilometers....
 
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