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Technical Discussions
Rolf Diederichs
NDT.net, Germany, Joined Nov 1998, 605

Rolf Diederichs

Joined Nov 1998
02:00 Feb-16-1998
More on the the Impact Echo Discussion

I am pleased to see such an in-depth forum discussion regarding the
Impact-Echo method.

As we follow the thread, we can see a very important aspect:

'A new method can be successfully established only if more than just
the equipment is developed and promoted'.

Operator qualification is an important issue.
Also ultrasonic testing can't be successful unless the complete package
is established at a very early stage.

When the equipment buyer becomes aware of this aspect when reading the
legal stuff in the operator's manual like
'successful usage is dependent on operator skill', it is too late.
Are they supposed to stop everything and recruit new personnel? Or enroll
their current employees in incredibly expensive training courses?

I read a lot of NDT literature but I haven't been able to find any
references that answer the following questions:

Are training courses for the Impact-Echo method offered?
Do associations like NDT societies define certain certification levels?

Any advice is appreciated.

Rolf Diederichs

William B. Streett
William B. Streett
00:57 Feb-18-1998
Re: More on the the Impact Echo Discussion
rses for the Impact-Echo method offered?
: Do associations like NDT societies define certain certification levels?

: Any advice is appreciated.

: Rolf Diederichs

Mr. Diederichs has asked questions about operator qualifications and
training for the use of NDT methods in general, and the Impact-Echo method
in particular.

I am not aware of any regular training courses offered on the Impact-Echo
method at this time. Two-day courses were offered at Cornell University
from 1992-1995, but the interest did not justify their continuation.

Impact-Echo is a powerful but complex method for nondestructive evaluation
of concrete and masonry structures. Some users have concluded that it does
not work as advertised, and the blame for failure has always been placed on
the method. In our view the blame sometimes rests with the user. Other
users who have invested the time and effort to learn the capabilities and
limitations of the method have found it highly useful. It is not a 'magic
box' that can always be used to tell what is inside a concrete structure.
It is best used in situations where the dimensions and make-up of the
structure are known, and when the engineer is searching for particular
kinds of internal flaws and defects that are known or suspected to be
present. Even in these cases it will fail if the user does not understand
the limitations as well as the capabilities of the method.

At this time all of the information necessary for learning to use
impact-echo effectively is available in the instruction manuals and books
that accompany our instruments. We are working to develop computer-based
demonstrations and tutorials that will speed up the learning process.

In the long run the acceptance of impact-echo will increase when the
fundamentals are taught in NDT courses at the university level. Special
discounts are offered on impact-echo test systems sold to universities (see

Some progress has been made. A standard method for measuring P-wave speed
and for measuring the thickness of concrete plates has recently been
approved by the American Society for Testing Materials (ASTM) and will be
published in the 1998 ASTM Book of Standards. At this time, the ASTM has
not assigned a number to this standard method. This means that in the U.S.
impact-echo is now an approved method for measuring the thickness of
concrete plates, such as new highway pavements, which until now were
measured only by coring. In the time required to drill, measure, and repair
a single core, as many as 30 thickness measurements can be made,
nondestructively and with equal accuracy, using impact-echo.

William B. Streett
Cornell University
Ithaca, NY 14850
e-mail: wbs3@cornell.edu


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