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 -

EXTENDE
EXTENDE, optimize your NDT inspections projects thanks to simulation.
633 views
Technical Discussions
Frits Dijkstra
Frits Dijkstra
02:58 Aug-25-1998
Restrictions of TOFD

The Time Of Flight Diffraction (TOFD) method, invented in the UK in the seventies, is now being used in several countries for routine NDT of welds. A method description exists, in the form of prEN 583 part 6. In The Netherlands, acceptance criteria for weld defects detected with TOFD were recently developed in a Joint Industry project, in which a.o. plant owners, manufacturers, NDT service companies and authorities were involved.

Although TOFD has been demonstrated to offer a very good probability of detection, experts agree that the technique is connected with restrictions in flaw detectability near the surface. The extent of the "dead zone" is, as previously explained by Schlengermann and Wuestenberg on this web-forum, influenced by a.o. signal length. In addition, it appears that misalignment (hi-lo) of welds in practice may increase the influence of the dead zone. On the other hand, high-resolution transducers and software algorithms such as straightening and lateral wave removal may help, but not in all cases.

It should be kept in mind that radiography and manual (pulse echo) UT have substantial restrictions as well, which we have comfortably lived with for many years. Therefore, it seems not unreasonable that TOFD is now accepted to replace RT or manual (pulse echo) UT for selected applications. Sometimes, combinations of TOFD with other techniques such as pulse-echo UT and / or magnetic particle inspection (just like other NDT methods sometimes need) will be required to meet defect detection requirements. Equipment allowing such combined inspection (TOFD plus pulse-echo) exists, e.g. RTD Rotoscan or Combiscan or others. Such combinations, if correctly applied, can lead to very reliable NDT, because "the best of two worlds" can be combined, using one technique as a "safety net" for the other.

TOFD is an NDT technique with high potential, and it is used on an increasingly large scale. But, it is not the ultimate solution to every NDT problem.




    
 
 Reply 
 
Jan Verkooijen
Jan Verkooijen
07:24 Sep-23-1998
Re: Restrictions of TOFD
I would like to endorse what Mr. Dijkstra has written
here. As allready stated during my comments at the ECNDT
at Kopenhagen, and also said here by Mr. Dijkstra,
it is clear that Time Of Flight Diffraction
is not the sole answer to all NDT problems in the world.
There are applications, such as the pre-service inspection
of welds, where it has been proven that TOFD is perfectly
capable of replacing an other technique in standard applications.
There are also cases where it is advisable to supplement TOFD
with other techniques should this be necessary to assure
the safety and reliability of the component, just as we
are used to do with the exisiting NDT techniques.
To be able to determine whether/when this is necessary, and which
techniques should be chosen, we still need more objective data
on POD, false call rate, sizing capabilities etc, not only
for TOFD, but also for other NDE techniques. It is
therefore that currently an international program of work is
being prepared to produce such data, to validate acceptance criteria and to
advise on training and certification standards for TOFD.
Only if we all work towards standards which are accepted
and adhered to, we can expect TOFD to become
available to NDT professionals as another valuable
tool to assure the integrity of components in industry.

: The Time Of Flight Diffraction (TOFD) method, invented in the UK in the seventies, is now being used in several countries for routine NDT of welds. A method description exists, in the form of prEN 583 part 6. In The Netherlands, acceptance criteria for weld defects detected with TOFD were recently developed in a Joint Industry project, in which a.o. plant owners, manufacturers, NDT service companies and authorities were involved.

: Although TOFD has been demonstrated to offer a very good probability of detection, experts agree that the technique is connected with restrictions in flaw detectability near the surface. The extent of the "dead zone" is, as previously explained by Schlengermann and Wuestenberg on this web-forum, influenced by a.o. signal length. In addition, it appears that misalignment (hi-lo) of welds in practice may increase the influence of the dead zone. On the other hand, high-resolution transducers and software algorithms such as straightening and lateral wave removal may help, but not in all cases.

: It should be kept in mind that radiography and manual (pulse echo) UT have substantial restrictions as well, which we have comfortably lived with for many years. Therefore, it seems not unreasonable that TOFD is now accepted to replace RT or manual (pulse echo) UT for selected applications. Sometimes, combinations of TOFD with other techniques such as pulse-echo UT and / or magnetic particle inspection (just like other NDT methods sometimes need) will be required to meet defect detection requirements. Equipment allowing such combined inspection (TOFD plus pulse-echo) exists, e.g. RTD Rotoscan or Combiscan or others. Such combinations, if correctly applied, can lead to very reliable NDT, because "the best of two worlds" can be combined, using one technique as a "safety net" for the other.

: TOFD is an NDT technique with high potential, and it is used on an increasingly large scale. But, it is not the ultimate solution to every NDT problem.




    
 
 Reply 
 
Jorden
Jorden
00:38 Feb-03-2007
Osbaldo
http://forum.finddesk.org/animal-health-pet.html


    
 
 Reply 
 

Product Spotlight

MUSE Mobile Ultrasonic Equipment

The MUSE, a portable ultrasonic imaging system, was developed for in-field inspections of light-weig
...
ht structures. The MUSE consists of a motor-driven manipulator, a water circulation system for the acoustic coupling and a portable ultrasonic flaw detector (USPC 3010). The MUSE provides images of internal defects (A-, B-,C- and D-scan).
>

Robotic laser shearography enables 100% inspection of complex, flight-critical composite structures

An article in “Composites World Magazine” showcases Non Destructive Testing of aero-structures
...
with Laser Shearography. Over the years Dantec Dynamics has supplied many solutions for the aerospace industry. Referring to specific customer projects several of these cases are examined to outline the advantages of using Laser Shearography for automated defect detection.
>

SITEX CPSERIES

Teledyne ICM’s CPSERIES has been designed with a view to revolutionizing the handling and perfor
...
mances of portable X-Ray sets. Despite having managed to halve the weight of similar portable X-Ray generators available on the market (while continuing to provide the same power output), the SITEX CPSERIES generators feature a shutter, a laser pointer, a beryllium window, an aluminum filter and two integrated diaphragms (customized sizes are available upon request). Without compromising the robustness and reliability for which ICM products are renowned, the small size and light weight of the SITEX CPSERIES will radically change the way that you perform your RT inspections. And you will see a positive impact in terms of both quality and return on investment (ROI).
>

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?
>

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