The Basics of Non-Destructive Material Testing - Part 1 5

[haileyk]

FYI, we just published an article on ENGINEERING.com based on a question at Eng-Tips Forums. I hope you enjoy it.

The Basics of Non-Destructive Material Testing - Part 1

Non-destructive testing methods test mechanical and other properties without permanently altering the subject, which saves time and money in product evaluation.

There are many companies that sell non-destructive machines to test material properties but they rarely explain how their methods work. Eng-Tips Forums member “afronova” posted the question, “Are there any good sites that inform about destructive and non-destructive material testing techniques?”

Well, afronova, there is now.

And so begins a three-part series on nine methods of non-destructive material testing. In part one, we discuss radiographic testing, ultrasonic testing and magnetic particle inspection....

 

[tbuelna]

Read the first part and it does a fairly good job providing a brief description of very complex subject matter.

After the basics of the nine NDI processes are covered, you might want to add more articles covering how to select the appropriate NDI process for different situations, the various process specs used in different industries, compliance and certification requirements for inspectors and equipment, economic/cost issues of selecting an NDI process, the relationship between NDI processes and engineering analysis used for certification, etc.

 

[haileyk]

Thank you for the great feedback. Those are great ideas.

 

[haileyk]

Part 2 in the series has just been posted on ENGINEERING.com.

The Basics of Non-Destructive Testing - Part 2

Continuing the three-part series on non-destructive testing we discuss dye penetrant inspection, eddy current testing and thermographic inspection.

 

[ehbadger]

Just to expand on the first of part 2 (if anyone wants more detail), there are different types of dye-pen testing (red dye, as pictured in the article) and a much more sensitive version, fluorescent-dye. The fluorescent dye-pen testing takes a bit more expertise to conduct and uses black-light to view indications. It is much more sensitive and useful for detecting very small indications (often invisible to naked eye even when you know it is there).

Example photo of indication attached.

 

[tbuelna]

haileyk- Good job with part 2.

One thing I would suggest adding to the dye pen process step 1, is the importance of etching rough machined surfaces. This will remove any smeared material that may be covering a surface defect. A very thin layer of surface material will be removed during the etching process, so it will need to be compensated for on very close tolerance features.

 

[haileyk]

tbuelna, thanks for the feedback. We will be amalgamating these three articles for a feature on

http://www.ENGINEERING.com

and will include etching in the process.

 

[haileyk]

The third and final part of the non-destructive testing series has just been posted on

http://www.ENGINEERING.com

The Basics of Non-Destructive Testing - Part 3

To conclude the three-part series on non-destructive testing we discuss leak testing, guided wave testing and visual inspection.

 

[IRstuff]

Hi Hailey,

I have minor disagreement with the Pro/Con table for leak testing. I think the only test that is completely operator dependent is the bubble test, since that's purely an eyeballed test. The other three involve measurable quantities, and assuming that there is a correct calculation equation and parameters, the calculated leak rate should not be operator dependent.

TTFN
I can do absolutely anything. I'm an expert!
faq731-376 forum1529

 

[haileyk]

IRstuff, I appreciate your criticism, it is a fair comment. I wonder though, at what point does something become "operator dependent"? For example, guided wave testing requires a transducer ring to be attached to the test pipe. It also requires someone to interpret the data obtained. Do we consider that to be an operator dependent test? I'd be interested to hear your thoughts.

 

[IRstuff]

Sure, I would agree that requiring more skill beyond reading numbers off a readout is and should be considered to be operator dependent. The test for this is whether the same operator or different operators would get the same or different results. If, for example, the helium leak test had a certain level of mechanical and test variability, an operator dependency would show up as a significant increase in that variability, while something that displays the numbers or records them to a computer would be expected to be operator independent, as far as the measurement is concerned. Nevertheless, the operator can certainly mess up a measurement in other ways, like lackadaisical or poor preparation, but those are generally considered to he procedural training issues. The bubble test requires a lot of interpretation regarding the size and frequency of the bubbles.

TTFN
I can do absolutely anything. I'm an expert!
faq731-376 forum1529

 

[tbuelna]

One other visual NDI process that is commonly used to detect problems with material properties is surface temper etch inspection (AMS 2649 or similar).