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Time of Flight Diffraction (ToFD) for Beginners

Speakers: Mark Nel and Gary Mathias

Date: Wednesday, 12 April 2023 

Time: 3:00pm - 4:00pm EST

Join speakers Mark Nel and Gary Mathias as they discuss Time of Flight Diffraction (ToFD). ToFD is a highly accurate Ultrasonic inspection technology primarily developed to inspect heavy walled pressure vessels and reactors in the nuclear industry. The application ToFD has spread to many other industry sectors and is now considered a mainstream technique often used in parallel with phased array and pulse echo. This talk delivers the basics of the technique, its application, advantages, and disadvantages.

Get to know the speakers:


Mark Nel started NDT life in 1980 as a radiographer on the SASOL II refinery in South Africa. After attaining SNTC-1A, SAQCC & PCN certifications in various methods, in the early 1990’s an opportunity arose to learn the relatively new Time of Flight Diffraction technology. As there was at the time no formal training or certification for ToFD in South Africa, the only educational route was on the job knowledge transfer from skilled British operators. Mark went on to apply, supervise and manage many ToFD inspection projects in South Africa, the Middle East, Pakistan, Tunisia and the USA.   In 2003 Mark joined Technology Design , a manufacturer of a range of advanced computerized UT systems in the United Kingdom. He describes the role as ”the tradesman’s face to a group of scientists and engineers”.  He was eventually also tasked with sales and his customer facing role has led Mark to visit NDT service providers and specialists in more than fifty countries. 


Mr. Gary Mathias has been involved in the NDT industry for more than 40 years. He earned an Associate in Applied Science Degree in Metals Technology from the Community College of the Air Force and earned a Bachelor of Arts in Business Management from Judson University.  He received his initial NDT technical training as an enlisted Airman with the Nebraska Air National Guard and the United States Air Force (USAF) Nondestructive Inspection School at Chanute AFB, Illinois.

Throughout Gary’s USAF career, he completed numerous advanced NDT training courses in composites, ultrasound, and radiography.  Gary is a Veteran and received the Nebraska National Guard Commendation Medal, the Air Force Achievement Medal, and the Air Reserve Forces Meritorious Service Medal.

Since his retirement from the USAF in 1999, Gary has held various roles in commercial NDT from manufacturing to product development and sales. He has worked for North Star Imaging, Parker Aerospace, Bell Helicopter, GE Inspection Technologies, and Sciemetric Instruments. While at GE, he led several technology transfers and commercial product development projects that included advanced computed tomography, pulsed eddy-current and robotics incorporating advanced phased array inspection of composite components.  Gary’s roles have given him a broad depth of NDT knowledge in the aerospace, automotive, rail, power generation and oil & gas industries, as well knowledge and application of NDT in various processes used in those industries such as castings, forgings, additive and general machining operations. Gary is a former Section Chair for the North Texas Section and served two terms as a Regional Director for Region 11.

Currently, Gary is a Regional Sales Manager for NDT Systems, Inc.  


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