Advanced DDF for inspection of thick Aluminium and Titanium

materials

Xavier Harrich, Alex Fidahoussen

1 Socomate International, France;

E-mail: Xavier.harrich@socomate.fr

Abstract

FAAST is a UT Phased Array system especially designed

to meet with high productivity inspection needs, thanks to

its outstanding capability at replacing multiple

conventional Phased Array systems working in parallel.

The FAAST technology has the capability to

transmit multiple sound beams, multi-oriented and/or

multi-focused in one single shot using standard phased

array probes. More features are integrated into the

instrument, such the possibility to shot at different

frequencies within the same shot. Furthermore, it allows to

work in full parallel or by using several active apertures

on the same probe. Hereafter is a list of applications where

the FAAST technology brings added value within the

Aircraft industry:

Using FAAST for special alloy and titanium

turbine disc inspection complying with Multi-zone testing

procedures aiming at the detection of down to

Ø0.4mm FBH at 2.5mm up to 140mm depth from the

surface. Multi-zone testing procedure requests Multi-

focused and/or Multi-oriented beams generation within a

single spray throughout a 2D matrix probe, reducing thus

considerably the inspection time per turbine disc.

Using FAAST in Aircraft Industry for aluminium

plate has been performed using the multiple focused

aiming at the detection of Ø0.8mm FBH from 2mm up to

160mm depth from the surface using a single 1D linear

128 elements phased array probe with a width of 120mm.

As the FAAST allows to generate all focusing delay laws

in one single shot, the scanning speed can reach up to

700mm/s while the performances answer the Aircraft

standards in terms of SNR.

Using FAAST in Bars application has been

performed using the multiple angles to detect Ø0.8mm

FBH and longitudinal notch. By using a curved phased

array probe, the FAAST generates the 0° and ±45° angles

in one single shot allowing thus an increase of speed by 3.

Other applications available on website or upon request.

1. Introduction

FAAST technology comes with a worldwide patent which

makes it a unique product within the NDT environment.

Due to its capabilities, we can provide outstanding

solution within Phased Array application. After presenting

its features, this paper will present some of our current

researches where it can be applied. As most of topics will

be related to Aerospace industry, FAAST can also be used

within the Oil & Gas industry for pipes inspection, high-

speed on-track rail inspection and any further applications

with high demanding requirements.

2. Capabilities of FAAST

In this section, presentation will describe capabilities of FAAST in comparison to traditional Phased Array instruments:

FAAST-PA is an industrial UT Phased Array

(PAUT) system which is much more powerful than

conventional Phased Array system. Thanks to its

technology, the FAAST system has the capability

to transmit multiple sound beams, multi-oriented and/or

multi-focused, through multi-element probes with only one

single shot, and then to process signals received from all

beams in real time.

This patented technology (WO03029808)

revolutionizes the NDT environment when speaking about

UT inspection due to its high-speed testing capabilities, as

it is able to replace several conventional Phased Array

systems running in parallel. At higher inspection speeds, it

offers even more savings due to the reduction of Phased

Array probes, mechanical parts, maintenance and

calibration time. Furthermore, the FAAST-PA incorporate

a real 80Vpp pulser for the PA channels. Using sinusoidal

signals, all the energy is concentrated within the

bandwidth of the sensor which allow better power and

results when inspecting thick or difficult to penetrate

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materials in comparison to square wave pulsers. Thanks to

this sinusoidal pulser, the resolution of the delay laws is at

1ns.

2.1 Multiple angles

The multi-angle is one of the prominent capabilities of our

Phased Array FAAST (PAUT) for generating multiple

beams using a multi-element probe and up to 16 beam

orientations or even more, are generated simultaneously

in one single shot. Signals are processed in real time, up to

16 directions simultaneously, but this does not restrict the

number of beams. This advanced acquisition mode can be

used with either 1D linear or 2D Matrix multi-element

probe.

2.1.1 Multiple angles using 1D Linear probe

With Phased Array FAAST, one single shot is required to

transmit several beams in the probe’s incidence plan, which can go up to 16 different direction in real time (but

does not restrict the number of beams) compared to

conventional Phased Array, where several sequential shots

are required to perform the inspection. Please find

hereafter the comparison with illustrations.

Figure 1: US Beam field simulation in water. Steering at different angles.

Figure 2: Example of FAAST generating multi-oriented beam - 3 different angles simultaneously. 1) Pulsing signal with delay laws. 2) FAAST US Beam field simulation in water.

2.1.2 Multiple angles using 2D Matrix probe

As it is possible to transmit several beams within a plan, it

is also true while using a 2D Matrix probe, allowing thus

to transmit all beams within space. In the same principle as

seen previously, all delay laws corresponding to different

angles are combined in pulsing signal. Below is an

illustration of a 2D matrix probe, where we activated

multiple elements, steering beams within space.

Figure 3: Example of FAAST generating multi-oriented beam - 8 different angles simultaneously. 1) Schematic view of US Beam. 2) FAAST US Beam field simulation in water (parallel plan to the probe).

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The FAAST-PA works the same way as conventional Phased Array instrument, however the patent allows us to generate all beams in one single shot, thanks to its sinusoidal pulser. 2.2 Multizone testing

The multi-focal is one of the other prominent capabilities

of the FAAST-PA, allowing the generation of multifocal

beams through a PA probe in one single shot. Using the

delay laws to focus at a given depth, the FAAST-PA can

combine, as for the angles, several delay laws to generate

multiple focusing beams at different level. This gives a

huge advantage regarding inspection speed, flexibility, but

also an increase in acoustical results. Not only in reception

with DDF (Dynamic Depth Focusing), the FAAST-PA is

multi-focusing in emission. This FAAST feature is what

we call “Advanced DDF”. Please find hereafter an

example where 3 focal delay laws are required.

Figure 4: US Beam field simulation in water. Focusing at different depths.

Figure 5: Example of FAAST generating multi-focused beam - 3 different focus simultaneously. 1) Pulsing signal with delay laws. 2) FAAST US Beam field simulation in water. 2.3 Multiple frequencies

Overall the above features, the last but not least capability

is the possibility to combine multiple frequencies within

the same emission, within the bandwidth of the sensor.

This allow the optimization of acoustical performances

while keeping high speed inspection. It will be introduced

in the next pages presenting trials and references.

3. Advanced DDF

In the following, we give two example cases where Advanced DDF is used. For reminding, we give a schematic principle of the acquisition.

Figure 6: Acquisition principle of Advanced DDF.

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As a comparison, we made 3 different types of acquisition:

1) 1 focal in Transmission-Reception 2) 1 focal in Transmission - DDF in reception 3) Advanced DDF / Multi-Focal in

Transmission, DDF in reception.

For each case, we made an electronic scanning with linear PA in contact on reference bloc which contains Side Drilled Holes (SDH) at different depth (see picture below).

Figure 7: PA configuration in contact on reference steel bloc.

Hereafter, you find B-scans of these 3 acquisitions.

Figure 8: Flaw detection comparison with: Left: 1 Focal in Transmission/Reception

Middle: 1 Focal in Transmission / DDF in Reception Right: Advanced DDF

As shown in figure 8, results are similar in defined focal area (30mm in steel- 5th SDH depth). Nevertheless, Advanced DDF allows to obtain smaller detection spot by comparison with two others acquisition, especially for deepest flaws.

3.1 Inspection of Titanium jet-engine turbine discs

To perform inspection, we use a 2D matrix PA probe at 10MHz central frequency.

Flaw sensitivity requested in this application is Ø0.4mm FBH, from 2.5 to 140mm depth. To cover all this depth, a maximum of 3 shots is needed, which lead to highly reduce time inspection compared to conventional methods. In practice, we have performed one shot for the very near surface zone, and 1 (or 2) other for the rest of requested inspection area. As the depth coverage could be important, we use Advanced DDF (as it is schematized Fig.6) to improve flaw detection, especially in term of SNR. Depth inspection is divided in 7 zones, to follow “Multi-zone” inspection performed with conventional UT. We have used Two Advanced DDF shots for :

1) 12.7 to 63.5 mm depth (Zones 2 to 5) 2) 63.5 to 139.7mm depth (Zones 6 and 7)

We give some C-scans obtained with titanium

reference blocs on some Ø0.4mm FBH depth and corresponding zone inspection by using Advanced DDF.

Figure 9: Ø0.4mm FBH detection with Advanced DDF Shots.

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3.2 Inspection of thick Titanium plate

To perform inspection, we use a 1D linear PA probe at 10MHz central frequency.

Flaw sensitivity requested in this application is Ø0.8mm FBH. In our study, we had flaws from 15 to 185mm. We have used virtual probe where only one Advanced DDF shot is applied for this depth range. An electronic scanning is done in addition to cover all probe and so increase the effective detection length.

We give in Figure 8, A-scans obtained with this Advanced DDF shot on some reference flaws.

Figure 11: Ø0.8mm FBH detection with Advanced DDF Shots.

4. Paintbrush parallel processing

4.1 Acquisition principle

We use the FAAST-PA capability to perform multiple post-processing in reception and in real time. This is a perfect feature which fits with an high speed inspection (700mm/s). Indeed, at this speed, it is difficult to carry out one (or more) electronic scanning in one shot.

To satisfy the criterion of speed control, the adopted solution is:

1) To use all the aperture of the linear PA in transmission. This “Paintbrush” mode allows to cover a wide area under the probe.

2) To perform, in reception, post-processing of several virtual probes by taking advantage of the available time between two US shots, as it is schematized Figure 9.

In practice, we shot simultaneously with all the

elements of the linear PA probe. Concerning the reception, to satisfy both near surface resolution and SNR criteria, we have used 2 different virtual apertures. The smaller one is used for near surface detection and the second one for deeper area. We represent the acquisition schematic in Figure 10.

Figure 12: Schema of inspection

The different post-processing emulate scanning, for which step and scan number are defined to fit inspection acoustic requirements, as for example a given repeatability (link to the effective beam width). Figure 10: Schematic timeline of acquisition

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4.2 Results on thick Aluminium plate

Flaw sensitivity requested in the application is Ø1.2mm FBH, from 3 to 165mm depth.

With this specific acquisition, we obtain good results in term of resolution. We managed to detect flaws at 1.5, 2 and 3 mm under the surface as we represent Figure 11.

Figure 13. Near surface Ø1.2mm FBH: 1.5mm (1) ,2.0mm (2) and 3.0mm (3) depth. Healthy area (4).

We have performed acquisition on different test block at the speed of 700mm/s. In figures below, we represent TFP detection at 3 (Figure 12) , 100 and 152 mm depth (Figure 13).

Figure 14. Near surface Ø1.2mm FBH at 3.0mm depth.

Figure 15. Deep Ø1.2mm FBH at 100 (1) and 152mm (2) depth.

5. Conclusions

As shown above, FAAST technology can provide high speed inspection and keep high acoustical results due to its capabilities. Dedicated for in-line inspection systems, and by combining several features, it can achieve outstanding performances to reduce inspection time and minimize number of Phased Array probes. As a conclusion, it shows that highest are the requirements, higher advantages FAAST would bring.

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