Time of Flight Diffraction (ToFD) Level-2

What is Ultrasonic TOFD?

Time of Flight Diffraction is an Ultrasonic technique developed originally to improve the sizing accuracy of flaws previously detected by other means. Early applications of the technique advanced from solely sizing flaws to applications relying on TOFD for principle detection means, this pioneering technology resulted in major flaws being missed due to poor application and a general lack of understanding by persons operating the equipment.

What are the responsibilities of an individual who is certified to UT TOFD Level 2?

An individual certified to UT TOFD Level 2 has demonstrated competence to perform NDT according to UT TOFD procedures. Within the scope of the competence defined on the certificate, Level 2 personnel may be authorised by the employer to:

  • Select the UT TOFD technique for the test method to be used;
  • Define the limitations of application of the testing method;
  • Translate NDT codes, standards, specifications and procedures into NDT instructions adapted to the actual working conditions;
  • Set up and verify equipment settings;
  • Perform and supervise tests;
  • Interpret and evaluate results according to applicable standards, codes, specifications or procedures;
  • Prepare UT TOFD written instructions
  • Carry out and supervise all tasks at or below level 2;
  • Provide guidance for personnel at or below level 2, and
  • Report the results of UT TOFD test

Syllabus specific to Ultrasonic Testing of Welds using Time of Flight Diffraction

1. Level 1 Specific Theory

1.1 Background to the importance of the TOFD Technique 1.2 History of TOFD development 1.3 Principles of TOFD 1.4 Diffraction process 1.5 Basic TOFD set-up 1.6 Types of TOFD scan 1.7 Summary of advantages and disadvantages of TOFD, including limitations 1.8 Basic hardware 1.9 Advantage of digital recording 1.10 Digitisation of the analogue ultrasonic signals 1.11 Amplitude 1.12 Sampling rate 1.13 Selection of frequencies for filtering 1.14 Amount of data collected during an inspection 1.15 Grey scale imaging and B-scans 1.16 Signal averaging 1.17 Pulse width control 1.18 Software 1.19 On-line 1.20 Analysis and off-line facilities 1.21 Precision and resolution 1.22 Beam spread considerations 1.23 Basics for calculation of beam spread 1.24 Example of selection of number of scans for an inspection 1.25 Choice of probe angle 1.26 Transducer size and frequency 1.27 Choice of probe centre separation 1.28 Calibration of setting of gain 1.29 Digitisation rate 1.30 Signal averaging and pulse width 1.31 No signals – common faults 1.32 Manual versus mechanical scanning 1.33 General 1.34 Manual scanning 1.35 Mechanical scanning 1.36 Sampling interval 1.37 Summary of choice of parameters for TOFD Scan 1.38 Introduction 1.39 Timing errors 1.40 Near surface problems 1.41 Off-axis error and back wall blind zone 1.42 Off-axis depth error 1.43 Back wall blind zone 1.44 Errors in couplant thickness, surface height variations and velocity 1.45 Large grained materials 1.46 Overall errors and monitoring growth 1.47 Overall errors 1.48 Monitoring defect growth 1.49 Data assessment – flaw characterisation 1.50 Shear waves 1.51 Pores and slags in TOFD records 1.52 Internal cracks 1.53 Upper surface breaking cracks 1.54 Lower surface breaking cracks 1.55 Effect of changing defect profile 1.56 Weld root flaws 1.57 Check transparency 1.58 Transverse flaws 1.59 Analysis software 1.60 Linearisation 1.61 Lateral/back wall straighten and removal 1.62 Parabolic cursor 1.63 Synthetic aperture focusing technique (SAFT) 1.64 Split spectrum processing 1.65 Curved surface 1.66 Complex geometry 

2. Level 2 Specific Theory As Level 1 but in addition:

2.1 Flaw sizing with the pulse echo technique 2.2 Comparison of flaw sizing accuracy for different techniques 2.3 Angular variation of diffraction signals 2.4 Effect of change in probe separation and importance of calibration with lateral and back wall signals 2.5 Change in probe separation 2.6 Importance of calibration 2.7 Error due to variations in couplant depth 2.8 Error due to variations in surface profile 2.9 Velocity error 2.10 Index point migration errors 2.11 Other errors 2.12 Multiple arcs 2.13 Procedure writing 2.14 Equipment and probe checks 2.15 Equipment checks 2.16 Screen height linearity 2.17 Amplitude linearity 2.18 Time base linearity 2.19 Probe index emission point 2.20 Beam angle 2.21 Beam spread 2.22 TOFD combined probe delay 2.23 Sensitivity 2.24 Resolution 2.25 Probe checks 2.26 Material velocity measurement 2.27 Probe frequency 2.28 Probe pulse length

We provide examinations for Time of Flight Diffraction (TOFD) testing, including examination for employers based schemes such as SNT-TC-1A, NAS410, EN4179, to Levels 2 and 3.

The requirements for Level 2 TOFD are: 40 hours training direct to Level 2 and 12 months supervised work experience (which can be obtained before or after the examination and must be attained within 24 months of the exam date).

The options for TOFD Level 2 examinations are:

Initial Candidate
Resit (Theory)
Resit (Practical)
Recertification

To be eligible for the  Level 2 examination, an eye test must be passed (near vision and colour) and candidates must hold Level 2 Certification in Ultrasonic Weld Testing The TOFD Level 2 examination includes a specific paper and practical exam.

The requirements for Level 2 TOFD are: 40 hours training direct to Level 2 and 12 months supervised work experience (which can be obtained before or after the examination and must be attained within 24 months of the exam date).

Overalls/Lab Coat
Safety Boots

Scientific Calculator

Bring some other form of identification showing a photograph, i.e. Passport or Photo Driving Licence.

All other equipment and training materials are provided by Cutech.

Protective gloves, protective eye glasses and plastic aprons are also available for the use of students.

Note: If you wish to bring your own UT PA set this must be approved by the tutor prior to commencement of the course.

Upcoming Course Schedule

Cutech Training, Examination & Consultancy Services
Cutech Training, Examination & Consultancy Services
Cutech Training, Examination & Consultancy Services
Cutech Training, Examination & Consultancy Services
Cutech Training, Examination & Consultancy Services
Cutech Training, Examination & Consultancy Services
Cutech Training, Examination & Consultancy Services
Cutech Training, Examination & Consultancy Services