What The Deuce Is Nondestructive Evaluation?

I realized today that I've been throwing around terms like "nondestructive evaluation" or "NDE" without actually bothering with definitions. Time to correct that particular oversight.

Nondestructive evaluation (NDE), also known as nondestructive testing (NDT), nondestructive inspection (NDI), etc., is just a catch-all for any method of physically examining something without damaging it (taking samples, cutting into it, etc.). In materials sciences, we're mainly looking to gauge the physical condition of a structure. Things like whether it's corroded or rusted, whether it has cracks or holes, that sort of thing.

As you may have already guessed, destructive evaluation is a process of physically examining something that also causes damage to the object in question. In general, destructive analysis is usually much more accurate than NDE, but of course that's at the cost of damaging the object. Damage is a subjective thing though and not everyone agrees on what's destructive and what isn't-take hydrostatic testing for example. To test whether or not a SCUBA tank is safe, it's pressurized to say twice its maximum pressure. Conventional wisdom is that a hydrostat is not a destructive test. My take is that it is a destructive test because by over-pressurizing the bottle you can create damage, e.g. if a tiny hairline crack forms.

My favourite analogy for NDE has always been the doctor's office. If your doctor thinks you might have broken your leg and orders an X-ray, that's nondestructive evaluation. If your doctor opts for exploratory surgery, that's destructive evaluation (cutting into your leg).

You can get more info on NDE from Iowa State's NDT Resource Center. A good public forum for NDT-ers is NDT.net. I'm a little hesitant to add Wikipedia's entry on NDT, but there it is. The page itself isn't very useful at the moment as it seems to have been hijacked for lack of a better word, but the links are useful anyway.

So there you have it. Hopefully you won't see "NDE" and think "near death experience" any more. :)