where expertise comes together - since 1996 -

The Largest Open Access Portal of Nondestructive Testing (NDT)

Conference Proceedings, Articles, News, Exhibition, Forum, Network and more

where expertise comes together
- since 1996 -

551 views
Technical Discussions
Hermann Wuestenberg
R & D
BAM Berlin, Germany, Joined Nov 1998, 26

Hermann Wuestenberg

R & D
BAM Berlin,
Germany,
Joined Nov 1998
26
04:14 Jul-02-1998
Questions on TOFD

Basically I agree with the commentaries of Udo Schlengermann, but would like to add some other points:
1. The dead zone does not only depend on the pulse length. We have to take into account the intensity relationship between the subsurface L-wave (also called lateral- , creeping- or longitunal headwave) and the diffracted crack tip indication. The subsurface L-wave has an other distance law than the the crack tip indication, that means it decreases much faster with an increasing distance between the probes than the diffracted tip signal. On the other side there must be regarded a dependency of the diffracted signal amplitude from the relationship between the depth of a surface breaking crack and the wavelength. For smaller depth of the crack the energy diffracted at the tip decreases. In consequence the "dead zone" for the detection and sizing of cracks close to the coupling surface is difficult to predict. For the practical application it seems to be reasonable to assume the values of 2 mm for 5 MHz and 6 mm for 2 MHZ as indicated by Udo Schlengermann as limitations of the method. Similar considerations are valid as well for the "dead zone" close to opposite surface. But there we have to do with much greater amplitudes from the backwall and hence stronger limitations for the detectability of near surface cracks have to be taken into account. A minimal detectable crack depth of 3 mm (for a surface breaking crack) must be assumed.
2. The coverage of a wall thickness to be inspected can be achieved by playing with basically 2 parameters:
- the distance between the probes and
- the soundfield divergency.
With on set of probes it should be possible the cover at least the 70 mm wall thickness as indicated in the European Prestandard 586-6, but only with two or three different probe distances. According to our experiences (see also the contribution of A. Erhard at the 7. ECNDT in Copenhagen, May 1998) the recommendations of that Prestandard are not very helpful. Since an increased beam divergency increases also the structural noise, a larger wallthickness requires more than one probe distance for the inspection. This leads immediately to a comparison with other traditional ultrasonic pulse echo inspections requiring multiple pathes and angles. For equal flaw detectability there is a wall thickness where the reliable detection of cracks requires an inspection with the conventional pulse echo technique using the well known corner effect as a much stronger physical interaction between an ultrasonic wave and a crack than the tip diffraction is.


    
 
 

Product Spotlight

NozzleScan: Radial nozzle scanner with probe skew

NozzleScan is a versatile manual scanning solution developed for the inspection of nozzle welds in
...
both set-through and set-on configurations. Available in both two-axis and three-axis instrument configurations and adaptable to cover a wide range of 90-degree nozzle sizes, from 3" upwards, on ferritic and austenitic materials.The transducer skew axis can also be adjusted, encoded and locked.
>

Lyft™: Pulsed Eddy Current Reinvented

PEC Reinvented—CUI Programs Redefined Corrosion under insulation (CUI) is possibly the greatest u
...
nresolved asset integrity problem in the industry. Current methods for measuring wall thickness with liftoff, without removing insulation, all have severe limitations. Eddyfi introduces Lyft — a reinvented, high-performance pulsed eddy current (PEC) solution. The patent- pending system features a state-of-the-art portable instrument, real- time C-scan imaging, fast data acquisition with grid-mapping and dynamic scanning modes, and flexibility with long cables. It can also scan through thick metal and insulation, as well as aluminum, stainless steel, and galvanized steel weather jackets. Who else but Eddyfi to reinvent an eddy current technique and redefine CUI programs. Got Lyft?
>

Ultrasonic Flaw Detector & Thickness Gauge: Smartor

SIUI’s newly launched Smartor is a combination of ultrasonic testing and ultrasonic thickness me
...
asurement. ●IP 66 ●Compact size: 198 (W)* 128 (H) *520 (D) mm ●0.9kg only with battery ●5.7" LCD with high resolution 640×480 pixels ●One-hand operation ●Multiple conventional UT functions ●Smart Test Wizard ●Weld Simulation
>

35 years of VOGT Ultrasonics!

This year we are celebrating a company anniversary! 35 years have passed since we first took our t
...
est device and swung the probe on behalf of safety. But our ultrasonic know-how goes back many years..
>

Share...
We use technical and analytics cookies to ensure that we will give you the best experience of our website - More Info
Accept
top
this is debug window
s