TOFD Training in Thane and Nagpur (Time of Flight Diffraction Level II) by Spark NDT

Time of Flight Diffraction (TOFD) Level II Training: 10 day batch in Thane and Nagpur

Time of Flight Diffraction (TOFD) is an ultrasonic technique that uses the diffracted waves from the tips of a defect, rather than the reflected echo, to locate and size it. Invented by Maurice Silk in 1974, it remains the ultrasonic method with the strongest capability for detecting planar defects and measuring their vertical extent through the wall, which is why it is a core component of automated ultrasonic testing on girth welds.

A TOFD examination uses a transmitter and a receiver placed on opposite faces of the weld and scanned along it with an encoder. The instrument records a B-scan in which the lateral wave, the diffracted signals from the upper and lower defect tips and the backwall reflection appear as separate features. Because sizing is taken from signal arrival time and probe position rather than from amplitude, the measurement is repeatable.

Spark NDT runs a 10 day TOFD course at Level II covering diffraction principles, probe and frequency selection, scan plan design, setup and calibration, acquisition on welds, signal identification, through-wall sizing, reporting, and software analysis and audit of TOFD data. Where a project needs full volumetric coverage, TOFD is combined with pulse echo phased array, and the course covers that combination as it is used in practice.

TOFD Training Course Details

Course	Time of Flight Diffraction (TOFD), Level II
Course duration	10 days
Training mode	Online live and offline classroom, plus hands on acquisition and data analysis
Equipment covered	Ultrasonic instruments in transmit receive TOFD mode, encoded linear scanning, wedges and probes for through-wall coverage, and offline TOFD analysis software
Trainer	ASNT Level III qualified NDT trainers
Training provider	Spark Institute of Nondestructive Testing
Locations	Thane and Nagpur, Maharashtra
Prerequisite	Working knowledge of conventional ultrasonic testing; Ultrasonic Testing Level II is recommended
Enquiries	info@sparkndt.com, +91 82080 65586

What You Will Learn in TOFD Training

• How diffraction at a crack tip is used for detection and sizing, and how it differs from reflection based pulse echo detection.
• The features of a TOFD B-scan: lateral wave, mode converted signals, upper and lower tip diffractions, and the backwall reflection.
• Probe frequency, element size, wedge angle and probe separation selection for the wall thickness and bevel being examined.
• Scan plan design: encoder calibration, probe offset, scan length, coverage of the weld and heat affected zone, and the through-wall leg depths the setup reaches.
• Setup and verification on reference blocks, sensitivity setting, and the checks that must be recorded before and after scanning.
• Data acquisition on welds at a scanning speed that keeps data quality, including the effect of PRF and encoder accuracy.
• Distinguishing defect signals from geometry signals such as root, mismatch, bevel and weld crown reflections.
• Through-wall sizing of a defect from upper and lower tip times of flight, and reporting the results against a written procedure.
• Combining TOFD with pulse echo phased array for zonal discrimination, and audit of TOFD data files.

TOFD Course Syllabus

1. Principles of TOFD: history and background, diffraction versus reflection, mode conversion, lateral and creeping waves, tip diffraction directivity.
2. Equipment, probes and wedges: transmit receive instrument configuration, probe frequency and element size, wedge angle and beam separation, encoded scanners and couplant requirements.
3. Technique and scan plan design: wall thickness and bevel geometry, probe placement and separation, leg depth coverage, scan length, encoder calibration and coverage of the HAZ.
4. Calibration and verification: reference blocks, sensitivity and signal to noise setting, checks before, during and after scanning, and the records a procedure requires.
5. Data acquisition on welds: scanning parameters, PRF and scan speed, data quality, surface condition and couplant, single and dual probe arrangements.
6. Data analysis: identifying the lateral wave, tip diffracted signals, mode converted signals and geometry indications, and separating relevant from non relevant signals.
7. Sizing and evaluation: through-wall sizing from tip time of flight, correction for probe separation and sound speed, limitations near the inner and outer surfaces, and acceptance against the applicable code.
8. TOFD with phased array: combining TOFD channels with pulse echo sectorial channels, zonal discrimination in automated systems, and merged C-scan interpretation.
9. Reporting, procedure and audit: writing the examination report, procedure content, records and the review of acquired TOFD data.

Reading a TOFD Image

A correctly acquired TOFD scan shows the lateral wave near the surface, the backwall reflection at the far surface and, between them, the diffracted signals from the tips of any planar defect. Defect depth is calculated from the arrival time of each tip signal and the known sound path, so the vertical extent is measured rather than estimated from amplitude. That is why TOFD is preferred where crack height is the critical measurement.

The same principle drives the scan plan. The probe pair is set on opposite faces of the weld so that the overlapping legs insonify the full wall thickness with the weld centred between them, and the bevel geometry, root face and any mismatch are taken from the weld drawing when the technique is written.

TOFD and PAUT: How the Two Compare

• TOFD gives the best probability of detection for planar defects and the most repeatable through-wall sizing, because it measures tip arrival times instead of relying on echo amplitude.
• PAUT uses the pulse echo technique familiar from conventional ultrasonics, produces sectorial views that operators and client inspectors read easily, and images the defect in multiple views from redundant information.
• TOFD is a through transmission method, so it needs access to both faces of the weld and accurate probe separation; PAUT can work from one side.
• TOFD signals near the inner and outer surfaces are limited by the lateral wave and the probe dead zone, the extent depending on transducer frequency, so complementary pulse echo or phased array channels cover those regions.
• For this reason automated systems for girth welds commonly run both: TOFD channels for sizing and phased array channels for detection and zonal discrimination.

On cross-country pipelines the combination is routine. Automated inspection systems running PAUT together with TOFD reach scanning speeds around 100 mm per second, which inspects a 36 inch diameter girth weld in about a minute.

Applications of TOFD

• Pipeline girth welds, automated and encoded, alone or with phased array.
• Pressure vessel and penstock shell and head welds.
• Refinery and petrochemical piping, headers and heavy wall joints.
• Power plant components and heavy fabrications where through-wall crack height governs acceptance.
• Long seam welds and plate butt joints in structural and shipbuilding work.
• In-service crack monitoring, where repeated measurement of the same defect is needed.

Who Can Attend TOFD Training

• Ultrasonic technicians adding a through transmission technique to their skill set.
• QA/QC engineers and welding or piping engineers who specify or accept TOFD results.
• Third party and client inspectors who review TOFD scans and sizing reports.
• Candidates preparing for automated ultrasonic work on pipelines and pressure equipment.
• Level II candidates under an employer written practice aligned to ASNT SNT-TC-1A.

Frequently Asked Questions

How long is the TOFD course at Spark NDT?

The Time of Flight Diffraction course runs 10 days at Level II. Durations for other methods are listed on our course durations page.

Is there a prerequisite for TOFD training?

You should already be able to carry out conventional ultrasonic testing. Ultrasonic Testing Level II, or equivalent experience, is recommended, because the course moves directly into probe selection, scan planning, sizing and procedure work.

Does TOFD need access to both sides of the weld?

Yes. TOFD is a through transmission technique with a transmitter on one face and a receiver on the other, so the two access points and the probe separation must be established before scanning. Where only one face is accessible, pulse echo methods such as PAUT are used instead or in addition.

Can TOFD detect surface breaking defects?

TOFD sizes defects well in the mid-wall region, but the zones near the inner and outer surfaces are affected by the lateral wave and the probe dead zone, and the extent depends on frequency and setup. Complementary pulse echo or phased array channels, and surface methods, cover those regions.

Is the training performed at the institute or on-site?

Both. Regular batches are conducted at the Spark NDT institutes in Thane and Nagpur, and corporate batches are arranged at a client premises where the client has the equipment and representative weld specimens.

Does Spark NDT issue the certificate?

Spark NDT is a training and examination centre working as an Outside Agency under ASNT SNT-TC-1A guidelines. It trains and examines candidates; certification is issued by the employer under its written practice, or by the applicable certification body.

Enquire About TOFD Training

For the syllabus, fees, hostel guidance and the next TOFD batch in Thane or Nagpur, write to info@sparkndt.com or call +91 82080 65586. Company and on-site batches are arranged for teams.