To determine the limitations of TOFD and assuming the outcome was to the client’s satisfaction: I would lead a team to carry out subsequent inspections in the field. The following is a brief overview of another success story.

1. DEVELOPMENT OF TOFD INSPECTION OF WELDMENTS ON 5.5MM THICK ALUMINIUM TANKERS.
Irvine Gilbert 2015
1 OBJECTIVES
Some time back, I was privileged to be involved in an exciting development to determine the limitations of TOFD on
Aluminium welds with a nominal wall thickness of 5.5mm. The following is a brief overview of another success story.
Success Criteria:
To determine the limitations of TOFD and assuming the outcome was to the client’s satisfaction: I would lead a team to
carry out subsequent inspections in the field.
The development was carried out in the Benelux and field inspections abroad. Our development leader is a highly
respected Level 3 professional (who is also a very good friend), together with PCN L2 TOFD Technician, supported by
myself providing Project Management & Scanner Technician duties.
In order to determine the limitations of the TOFD technique, the following tests were carried out:
1. Measure the sound velocity on the extrusion and plate, in order to find the values and amount of difference
o Rationale being: The more difference there is, then the more the measuring error would be.
2. Measure with TOFD in order to determine the maximum depth that a defect can be detected as a function of the
plate thickness – taking into consideration the groove length. For example: If the groove length is present, then
we cannot measure below.
3. Measurement on artificial defects in order to determine the minimum defect height that can be detected at
maximum measuring depth
4. Various measurements in order to find & determine optimum settings
Procedure Equipment Personnel
This inspection approach is based on
ISO 10863:2011
TD Pocketscan Acquisition System,
Rhosonics 15MHz Probes,
WREN Scanning Frame & Encoder
Level 3 TOFD (amongst others)
Technical Authority
PCN L2 TOFD, PA, UT, MT, DP
PCN L2 PA, UT & MT
2 MEASUREMENTS & CALCULATIONS
Time for a bit of hands-on: I proceeded into the workshop (naturally wearing the relevant PPE), and proceeded to
gingerly cut the test piece into 3 samples.
This was taking too long for the workshop manager who took over, and expertly machined the sample in double quick
time

2. DEVELOPMENT OF TOFD INSPECTION OF WELDMENTS ON 5.5MM THICK ALUMINIUM TANKERS.
Irvine Gilbert 2015
Using 0 degree probe we achieved the following measurements
SAMPLE # PLATE THICKNESS TIME 1ST BACKWALL TIME 4TH
BACKWALL
1 4.6mm 1.82 micro sec 6.16 micro sec
2 4.65mm 1.84 micro sec 6.20 micro sec
3A 9.32 mm 3.28 micro sec 11.99 micro sec
3B 9.35mm 3.28 micro sec 12.01 micro sec
Using the following logic:
 Plate thickness x No. skips from 1st
measurement to 4th
measurement = Total distance covered (mm)
 We know that the number of skips from 1st
measurement to 4th measurement = 6
 We can measure the total distance covered from 1st
to 4th
measurements (mm)
 Also the time taken to do those skips = Time from 4th
- 1st
(micro seconds (10-6
)
Calculations
SAMPLE TOTAL DIST TIME TAKEN VELOCITY
No. mm Micro sec m/s
1 4.6x6= 27.6 6.16-1.82= 4.34 27.6 (x 10−3
) / 4.34 (x10-6
) = 6360.0
This procedure was repeated for all four samples to give an average velocity (Plate 3 having 2 measuring points):
6360.0+6339.0+6420+6426.1 / 4 = 6386.25 m/s +/- 47 m/s.
2.1 REFERENCE PLATE
Sample 3, was designated the reference plate, which would be used to calibrate for subsequent inspections
1mm dia middle hole drilled (A)
T
0.5 +/- 0.3 mm deep x 1mm wide notch underneath
Scan in direction of the weld
1mm dia 1.15mm (+/- 0.5 mm) from bottom (B) @ ¾ Thickness (T)
We discovered that due to discrepancies in sound velocity caused by the orientation of the grain structure: Scanning in
the direction of the weld gave the lowest sound velocity – thereby providing the best results.
Detection of the side drilled holes on this piece was unsatisfactory, due to the thinness of the plate.
The height of the notch, however could be detected and measured at 0.7mm.
2.2 TEST PIECE WELDS
Side drilled holes were inserted into a designated Test Piece, which would then be used for sensitivity checks.
1mm dia. Bottom Hole @ ¾ T +/- 0.5 mm 1mm dia. Middle Hole @ 1/2T+/- 0.5 mm

3. DEVELOPMENT OF TOFD INSPECTION OF WELDMENTS ON 5.5MM THICK ALUMINIUM TANKERS.
Irvine Gilbert 2015
3 RESULTS.
3.1 SCAN ON TEST PIECE (PLATE 3)
The scans demonstrated that the maximum thickness that can be inspected is up to the depth of the adjacent groove.
The holes are clearly detected and the following values were measured for Plate 3 (reference piece)
Plate 3 results
File name/description hole Depth Top of
indication
Bottom of
indication
Throughwall
height
plate 3 1mm sdh plate bottom 240913 IW_TOFD1.scn ¾ T 3.95 3.95 5.38 1.4
plate 3 1mm sdh plate bottom 240913 IW_TOFD2.scn ¾ T 3.95 5.25 1.3
plate 3 1mm sdh plate middle 240913 IW_TOFD1.scn ½ T 3.22 3.42 4.72 1.3
plate 3 1mm sdh plate middle 240913 IW_TOFD2.scn ½ T 3.22 3.61 4.75 1.4
Height of indication was determined at 1.4mm with an accuracy +/- of 0.5mm
Detection threshold of +/- 0.5mm was determined.
3.2 SCAN VIEWS OF TEST PIECE WELDS WITH DEFECT
The following samples were subsequently tested (Labelled Plate1 & Plate 2). These samples have known defects and
also have a protective coating coated
The test scans were conducted using optimum settings which have been determined & included in the Procedure
4 SUMMARY OF LABORATORY RESULTS.
1. The sound velocity variation of the samples is less than 10% and will not significantly influence the depth
measuring accuracy.
2. Maximum thickness that can be inspected is up to the depth of the adjacent groove
3. The side drilled holes could be detected and sized. The estimated accuracy for depth measurement is
0.5mm. The notch could be detected and sized. The estimated detection threshold id 0.5mm
4. The best set up was established and described in the Procedure

4. DEVELOPMENT OF TOFD INSPECTION OF WELDMENTS ON 5.5MM THICK ALUMINIUM TANKERS.
Irvine Gilbert 2015
5 IN THE FIELD
Equipped with the tools and skills necessary to carry out inspections, we flew off to where the tankers were stationed,
and set about site establishment.
A scan plan was drawn up (below), and relevant H&S put in place: Risk Assessments, PPE, Working at heights, etc.
A trip to the nearest Garden Centre, we acquired
a pressurized water bottle and some thin bore
water hose: Makes the perfect couplant feeder.
Armed with a licence to operate a Cherry-Picker,
and Safety harnesses: We were good to go!
The Client approved our inspection plan, and
was eager to validate the results.
This would be achieved by cutting out plates that
were inspected and then cutting through where
the indications were marked.
6 RESULTS: WINS ALL ROUND - AGAIN
 We achieved our objectives:
o The Development was successful in delivering a Technique which was repeatable
 The client was happy that we were able to acquire accurate data which would enable them process this into
relevant engineering information, which would be beneficial to their business/engineering processes.
 I gained valuable experiences including:
o Project Management responsibility for delivering both Development and Field trials
o Insights into the inspection development & validation process
 Again, A satisfied customer and more new friends!
At position 424mm:
Top of indication=3.423mm from
top surface
Bottom of indication = 5.254mm
from top surface
Giving a through wall height of
5.254-3.423= 1.831mm
After cutting, Actual measurement
was deemed to be 2mm