advanced ultrasonic inspection in slovenia · advanced ultrasonic inspection in slovenia dr. uros...
TRANSCRIPT
ADVANCED ULTRASONIC INSPECTION IN SLOVENIA
dr. Uros Zupanc,1 dr. Darjo Zuljan, dr.-Ing Miro Uran
INSTITUT ZA VARILSTVO d.o.o., Ljubljana, SLOVENIJA 1Phone: 00386 41 312 038; E-Mail:[email protected]
ABSTRACT
Phased Array (PA) ultrasonic testing is an advanced method of ultrasonic non-destructive testing
(NDT) with growing applications in industrial and medical fields. Phased Array probe consists of
many small ultrasonic elements, each of which can be pulsed individually by advanced electronics.
Electronic focusing permits optimizing the beam shape and size at the expected defect location and
thus significantly increases probability of defect detection. The data from multiple beams are put
together to make a visual image showing various projections through the inspected object.
The conference paper presents practical experience of PA inspection in five typical industrial
applications in Slovenia: (a) airplane wing corrosion inspection, (b) steam pipeline tubes inspection
in thermal power plant with thermal cracks, (c) weld inspection of water pipeline in hydro power
plant, (d) inspection of bolts on old ski-lifts and (f) railway inspection of train axes.
Key words: Ultrasonic testing, NDT, Phased array, TOFD, Olympus Omniscan
1. INTRODUCTION
Phased Array (PA) ultrasonic testing is an advanced method of ultrasonic non-destructive testing
(NDT) with growing industrial applications. Ultrasonic phased array systems can potentially be
employed in almost any inspection where conventional ultrasonic flaw detectors have traditionally
been used. Weld, casting and forging inspection, crack detection and corrosion evaluation are the
most important applications in a wide range of industries including aerospace, power generation,
petrochemical, pipeline construction, maintenance, structural metals and general manufacturing.
The phased array testing offers significant advantages for conventional ultrasonic testing of
components due to its extended informational content.
A PA probe consists of many small ultrasonic elements, each of which can be pulsed individually
by advanced electronics controlled by a PA machine. The benefits of phased array technology over
conventional UT come from its ability to use multiple elements to steer, focus and scan beams with
a single transducer assembly. Beam steering, commonly referred to sectorial or linear scanning, can
be used for mapping components at chosen angles and chosen focal laws. Electronic focusing
permits optimizing the beam shape and size at the expected defect location to increase probability
of defect detection in volumetric inspection. Focusing can significantly improve signal-to-noise
ratio. The data from multiple beams are put together to make a visual image showing various
projections through the inspected object. This can greatly simplify the inspection of components
with complex geometry. More about the PA ultrasonic technique can be read in [1-2]. Additional
evaluation of diffraction signals by TOFD (Time-of-flight diffraction) technique in weld
applications allows fast inspection, accurate sizing of material flaws by means of corresponding
projection images. The TOFD technique relies on the interaction of ultrasonic waves with the tips of
discontinuities. This interaction results in the emission of diffracted waves over a large angular
range. Detection of the diffracted waves makes it possible to establish the presence and sizing of the
imperfection. Detail of TOFD technique can be found in [3-5].
The conference paper presents some practical experience of PA and TOFD inspection Slovenia. The
advanced ultrasonic inspection was performed to evaluate potential corrosion damage in complex
wing structures made of aluminium high-strength alloy. The NDT inspection in duration of just few
hours made it possible to highly reduce cost of alternative visual inspection with prior wing
Mor
e in
fo a
bout
this
art
icle
: ht
tp://
ww
w.n
dt.n
et/?
id=
1604
7
dismantling in time of few hounded hours. Corrosion damage was found and was properly repaired.
PA inspection of a part of steam pipeline in thermal power plant is presented. In second application,
the water injection system in steam control unit was evaluated using PA system where thermal
cracks perpendicular to back wall of pipeline were found. Indications of potential thermal cracks
were evaluated using linear and sectorial scans. In part three the results of combined automated PA
and TOFD inspection of welds are presented. Complex weld geometry made conventional UT
inspection very difficult, so automated PA-TOFD inspection was proposed and performed. Typical
indications of found imperfections are presented. On ski-lifts mechanism corrosion and worn level
detection of surface of bolts using phased array was performed. Evaluation with use of PA
technique makes it possible to inspect all bolts in the mechanism fast, without dismantling and with
very high level of material corrosion and/or wear detection. Conventional inspection of wagon axes
in present for quite a long time. But due to complex inspection geometries and thus need for
custom-made ultrasonic probes, PA inspection shows great future potential. Visualization of crack
indications helps inspector for faster and much more reliable inspection. All records of axe
inspections can be easily recorded and stored for any later re-evaluation and comparison.
2. RESULTS AND DISCUSSIONS
2.1 Corrosion inspection on aeroplane wings - PA inspection
Corrosion deterioration of aluminium structure in chloride atmosphere combined with material
fatigue indicated high potential danger. Critical areas at multiple bolting locations and reinforced
spars were inspected in total length around 30 meters per each wing. The scanning was performed
on individually marked areas of 500 mm in length and 40 mm in width and than detailed evaluated.
For inspection the Olympus Omniscan MX16-128 machine was used with specialized 5 MHz 64
elements probe with special wheel encoder presented on Figure 1. In the inspection corrosion was
indicated by a reduction of backwall echo of more than 4 dB with, i.e. corresponding thickness
reduction of more than 10%. Calibration was performed using reference block with three thickness
steps (5, 10 and 15 mm) with machined spotfaces representing 10 % and 20 % thickness reduction
on each reference thickness (Fig 1).
Fig. 1. Equipment used for airplane wings inspection (left). The calibration reference block with
machined spotfaces at different depths (right)
Figure 2 presents typical corrosion indication recorded in corrosion inspection by Omniscan MX
software. The Omniscan display was divided in three reference scans known as A-C-C view.
Amplitude A-Scan waveform presented backwall echo signal and two phased array plan-type C-
Scans presenting top view of inspected area. C-Scan in monochrome contrast was selected as
amplitude reference (A%). Bottom coloured C-Scan was selected as thickness change reference.
Yellow colour indicated 10% thickness reduction and green colour indicated approximately 20%
thickness reduction.
Fig 2: Typical corrosion indication presented in A-C-C view mode. Corrosion indication area of
approximately 40 x 100 mm was found around the bolts.
Fig. 3: Corroded area after dismantling of wing structure. Pen on the right photo served as a
reference dimension. The corroded areas are marked with an arrow.
2.2 Inspection in steam pipeline – PA inspection
The water injection pipeline system in steam control unit was evaluated using PA system where
cracks due to thermal shocks may occur. Inspection was performed with linear and sectional
scanning using standard 5 MHz 64 element Olympus IMS probe (5L64) with zero degrees wedge
and attached wheel encoder. In water injection control system cracks due to thermal shock were
found. Ultrasonic indications of potential thermal cracks were evaluated first using linear scan,
where quite scattering backwall echoes were noticed due to position of thermal cracks
perpendicular to inner wall surface (Fig 4).
Corroded area
Corroded area
Fig. 4: Cross-sectional side view B-Scan image (left) and top view C-Scan (right) of inspected
pipeline indicating rough surface and thus possible thermal cracks.
With the additional PA inspection using sectorial scan it was possible to confirm crack indications
and also to measure the depth of individual crack indications. In the water injection unit with mean
wall thickness between 42 – 44 mm thermal cracks measured up to 10 mm. Due to highly cracked
pipeline inner surface the complete steam control unit pipeline was replaced. Section of eliminated
pipeline material is presented on Figure 5.
Fig. 5: Highly cracked inner surface due to thermal shocks (left), detailed side view of eliminated
pipeline material (right)
2.3 Weld inspection – Combined TOFD and PA inspection
Weld inspection of underground water pipeline is quite complex as around 100 pcs of welds to be
evaluated with diameter of ca 3 meters. Furthermore weld geometry makes inspection even more
complex - welded on backing plate, inspection possible just from inner side of pipeline, on some
sections different thicknesses of joined pipes are used. Due to increased danger of cracks in weld
root (pipeline already ca. 30 years in service) combined PA-TOFD inspection was chosen to
maximize probability of defect detection. Special calibration blocks were prepared for crack
inspection sensitivity and precise positioning. Two common calibration blocks are presented in
Figure 6. Acceptance criteria indicated that no crack indications were allowed. The newest PA
machine was used Olympus IMS Omniscan MX2 32-128 with flex-scanner, wheel encoder, 5L16
PA probes and 5 MHz TOFD probes with 60º wedges.
Fig. 6. The calibration block design for two typical expected cracks in the pipeline welds
PA-TOFD inspection procedure is setup with help of using special software ES Beam Tool from
Eclipse Scientific [6]. The program enables us visualisation of beamset for proper index position of
both PA probes and TOFD tandem probes and setup of appropriate focusing depths. As presented
on Figure 7a beamset of PA probe on left side is focused on weld root and backing plate (blue),
opposite beamset of PA probe on right side is focused on weld toe (red). TOFD tandem probes are
setup to maximal sensitivity of volumetric inspection in the middle thickness of the weld (Fig 7b).
a.) Position of both PA probes according to weld geometry
b.) Position of TOFD probes according to weld geometry
Fig. 7. Inspection procedure for PA and TOFD inspection using ES Beam Tool [6].
Result of weld inspection can be directly evaluated on Olympus Omniscan, but can also be detailed
inspected on notebook or PC with Olympus Tomoview software. Figure 8 presents PA inspected
weld section of 700 mm in length with some comments written. Results are presented in rectified
A-scan waveform, cross-sectional B-scan profile and sectorial S-scan (A-B-S view) of one PA
probe. Interpretation of results by individual PA probe can be made and further one compared with
TOFD images (Figure 9).
Fig. 8. Inspection results in A-B-S view with comments of one PA probes evaluated in Tomoview
software. PA probe is focused on weld toe.
Fig. 9. TOFD inspection results focused on the middle part of the weld
2.4 Inspection of bolts on old ski-lifts ion
On ski-lifts mechanism corrosion and worn level detection of surface of bolts using phased array
was performed. The evaluation of bolt surface is possible just by disassembly of the mechanism and
100% visual inspection, but with long time inspection and high cost. Evaluation using PA technique
makes it possible to inspect all bolts in the mechanism fast and with very high level of corrosion
detection. Comparison of corroded/worn vs. smooth surface of bolts was compared. The diameter of
bolt was 45 mm. The tests were as follows: (a) longitudinal waves using a probe 5L16-A10 with
direct contact at the top surface of the bolt and (b) sectorial scanning using angle beam wedge N60S
for shear waves and 5L16-A10 PA probe.
Fig. 10: Ski-lift mechanism with location of a bolt (left). Worn and corroded surfaces of
disassembled bolts (right).
On Figure 11 are presented sectorial scans at angles between ± 60° using longitudinal waves of non-
corroded bolt on left picture, corroded and worn on right picture. The difference of inspected
surfaces can be easily evaluated.
Fig 11: Sectorial scan with longitudinal waves of non-corroded surface of bolt (left) compared to
bolt with corroded surface (right)
2.5 Railway inspection of train axes
Conventional ultrasonic inspection in combination with magnetic particle inspection of wagon axes
in present for quite a long time. But due to complex inspection geometries with potential cracks on
axes hidden in the wagon wheels assembly, few thousand inspected axes annually, need for
experienced NDT inspectors and custom-made conventional ultrasonic probes (3, 5 and 7 degrees
longitudinal probes and 37-39 degrees and 54-60 degrees angle probes), PA inspection with
automated clamping system shows great future potential. Daily inspection records can be easily
recorded and stored for potential later re-evaluation and comparison.
Corroded areas
Fig. 12: Sectorial scan with shear waves with angle PA probe of non-corroded surface of bolt (left)
compared to bolt with corroded surface (right)
Fig. 13: Sample with artificial crack for ultrasonic calibration (left) and real axe sample inspection
(right)
Fig. 14: Total 360 degrees sectorial phased array scan of an axe with diameter of 152 mm. At angle
of 55 degrees hidden crack under the wheel assembly was found with the length of around 55 mm.
Corroded area
Worn area
Crack
3. CONCLUSIONS
Portable PA machines are commercially available for expanding range of applications due to their
high speed testing, multiple beamsets and visualization of inspection results. With increasing
number of machines sold worldwide or especially in Europe more inspectors and experts in NDT
community are aware of advances of using advanced NDT methods. Also the cost of investment in
equipment is decreasing. The phased array solutions are not only designed for high-tech industries
such as nuclear, aerospace, petrochemical, military, composites etc. but also for manufacturing and
thus also for applications in weld, casting and forging sectors. Particularly for weld applications
Olympus software “Ray tracing” was developed to visualize the inspection to unskilled inspectors.
But on opposite side inspectors will need some more time to understand and master the advance UT
techniques. Standardization of PA procedures, techniques, inspection criteria, qualification and
certification of personnel is slowly being implemented in manufacturing industry. First prEN and
ASTM standard are already available, but higher progress is expected in coming years.
4. REFERENCES
1. Olympus IMS Phased array tutorial. Accesed at: http://www.olympus-ims.com/en/ndt-
tutorials/phased-array. Web: 2.8.2013
2. Dube N., Phased Array Technical Guidelines, Useful Formulas, Graphs and Examples,
Advanced Practical NDT Series, R/D Tech Corp., Canada, 2005, ISBN 0-9735933-1-8
3. EN 583-6, Non-destructive testing – Ultrasonic examination – Part 6: Time-of-flight diffraction
technique as a method for detection and sizing of discontinuities
4. EN ISO 10863, Non-destructive testing of welds - Ultrasonic testing - Use of time-of-flight
diffraction technique (TOFD)
5. EN 15617, Non-destructive testing of welds – Time-of-flight diffraction technique (TOFD) –
Acceptance levels
6. Software ES Beam Tool, Eclipse Scientific Accesed at:
http://www.eclipsescientific.com/Software/software.html. Web: 2.8.2013