Transcript
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Advanced NDT
Long Range Ultrasonic Testing (LRUT)
Acoustic Emission Testing (AET)
Time of Flight Diffraction (TOFD)
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LONG RANGE ULTRASONIC TESTING
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Long Range Ultrasonic Technique (LRUT)
HOW IT WORKS Torsional or longitudinal guided waves are induced into
the pipe body and propagated along the pipe segment
being inspected. When these guided waves identify ananomaly or Pipe feature, the waves convert into laminar
waves and reflect back to the LRUT Toolsoriginal location.
We use a laptop computer to digitally capture the results.
The time-of-flight for each signature is calculated to
determine it's distance from the tool.
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Conventional UT measures the wall thickness at a spot,
while Guided Wave Ultrasonics can identify locations of
metal loss along a length of the pipe
WeldMetal loss Metal loss
FlangeConventional
Ultrasonic Test
Weld Metal loss Metal loss
Guided Wave
100%
Inspection
LocalizedInspection
Convent ional ult rasonic inspect ion prov ides a local th ickness measurement
GWUT Inspect ion p rovides d etect ion of b oth in ternal and
external corrosion typically for 100 or more down the pipe.
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Guided waves, typically between 3075 KHz, are
introduced into the pipe
An array of piezoelectric crystals arepositioned in modules that typically
hold two transducers each. The
modules are spaced around the pipe
under an air bladder which whenpressurized forces the units against
the surface. The individual crystals
oscillate at the frequency at which
they are excited and transmit the
wave into the pipe.
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The power and durability of todays electronics
has made it possible to field the GWUT system
in a compact package
Pressurized bladder
containing the array of
piezoelectric crystals
Laptop
computer
Field
electronics
Umbilical cableconnecting
electronics to
transducers
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LRUT - APPLICATIONS
Road and river crossings
Risers
Offshore topsides pipe work Jetty lines
Refinery pipe work
Chemical plant pipe work Tank farm link lines
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LRUT - Features
o Diameters if 1.5 to 48.o 100% Coverage
o Test Range Typical 30m
180m in Ideal conditions
o Production rate approx. 600m per day under ideal conditions
o Service temperature up to 120 C
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LRUT - Performance
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Advantages of LRUT
Can test long distances of pipe from a single access point
Has developed into an effective screening tool useful in locating and rankingareas of corrosion; thereby minimizing the amount of follow-up inspectionneeded to determine the integrity of piping.
Can be used on in-service pipelines
Both internal and external corrosion can be identified
Current commercial systems are packaged in a small number of durablecomponents. The systems are easily transported and quickly setup in the fieldwith preliminary results available at the time of the test
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Limitations of LRUT
Complicated evaluation of data by highly trained operators is required becauseof the complex signals involved
Dimensions of corrosion (wall loss, longitudinal length, profile) cannot bedirectly determined
Significant corrosion can be missed, especially localized damage
The scattered signal cannot be directly equated to a specific area or volume ofloss due to a lack of an absolute calibration standard
Many field conditions exist that limit the distances that can be effectivelyinspected and that cause artifacts which can complicate analysis.
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Example of corrosion that would not have been noted with
Guided Wave on a buried piping segment
This is a photograph of the
corroded area which caused
the leak in a buried 6 line.
Along the line drawn, the
cross-sectional area of the
walled pipe is approximately
9.62 square inches, while the
area lost to corrosion through
the hole is 0.5 square inches.
This is a loss of approximately
5.2% of the cross-section. It
would not been seen in a scan
since the section was buried.
However, if this line was
above-grade and exposed the
corrosion probably would have
been noted as a minor
anomaly
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AET
Acoustic Emission examines the behaviour of
material under stress.
Acoustic Emission is the spontaneous release
of energy when material undergoes
deformation for ex: erosion, corrosion,
leakage, plastic deformation etc.
AE detects defects only when crack grows.
A static defect will not be detected by AE
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AET
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AE Testing of Pressure Vessels
Example of Transducers Distribution on Vessel's Surface Typical Results Representation of Acoustic Emission Testing
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Advantages of AET
Inspect 100% of the part/vessel (global
inspection)
Detect discontinuities significant to the part's
structural integrity
Can be applied in-service
Little/no disturbance to insulation
Wide temperature range (Cryogenic to High
temperature )
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Limitations of AET
Cannot size discontinuities (depth, length)
Cannot detect flaws if improper stressing
method is applied
Cannot detect dormant discontinuities, notassociated with an active damage mechanism
AE testing is sensitive to process noise exceedingthe detection threshold
Evaluation criteria do not exist in form ofcommonly accessible data ; service providerdependent.
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TIME OF FLIGHT DIFFRACTION
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TOFD
The TOFD technique is a fully computerized system able toscan, store, and evaluate indications in terms of height,length, and position with a grade of coverage, accuracy andspeed not achieved by other ultrasonic techniques.
The TOFD technique is based on diffraction of ultrasonicenergy from tips of discontinuities, instead of geometricalreflection on the interface of the discontinuities.
This phenomena makes TOFD effective for identifyingcracks and lack of fusion located along the vertical axis ofthe weld (in particular for narrow gap preparation) or withany other orientations, because defect detection is notaffected by unfavourable orientation to the primary soundenergy angle
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TOFD Principles
Four different types of waves are involved in theconstruction of a TOFD image:
longitudinal wave generated by the transmitterand partially transformed in spherical wave whenthe beam crosses the tip of a defect
the lateral wave that propagates near the surfacebetween the two transducers
the longitudinal wave reflected by the backwall
the shear waves generated by the modeconversion L/T on the interface of discontinuities
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Two probes of opposite beam directions are used in a transmitter-receiver arrangement
Emitter Receiver
Case of an embedded crack
1
2
3
2
scanning
Time of flight
amplitude1
2 2 3
2 : bottom diffraction
scanning
time
1 : lateral wave
3 : backwall echo
2 : top diffraction
TOFD
60 L-Waves inspection
2.25 MHz frequency
TOFD (Time of Flight Diffraction Technique) use in NDT to detect and characterize flaws.
Echoes are used to size the defect
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Transmitter Receiver
Surface breaking crack
1
2
3
Transmitter Receiver
Backwall breaking crack
1
3
2
surface breaking flaw will prevent lateral wave
to be transmitted: interruption of the lateral
wave
Depending on size and position of the flaw shadowing effects can be observed
Shadowing effect may arise to backwall echo as
the beam will be partially reflected by the flaw
TOFD inspection principle
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Application Pre Service inspection partly and fully welded welds, 6-... mm (experience
up to 350mm)
Diameters from DN 100 (4 inch)
In Service Inspections (up to 450C)
Piping (weld) inspections
Root corrosion and erosion inspection Detection and monitoring of hydrogen damage
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Advantages
Detection is independent of the orientation of the indication,resulting in a higher probability of detection (POD )
The reliability of the technique notably reduces the chance that animportant error is missed. The missing of an important error canlead to an unplanned shut down
Reproducibility and measuring errors proved < 0.5 mm deviation Consistent results before and after PWHT
Electronic and/or hard copy available
Immediate result
NO radiation, so weld and construction activities can continue,
because there is no need to evacuate large zones for performingthe inspection
Defect monitoring is possible (during production)
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Limitation
Only applicable on fine-grained steel (low or
non alloyed steel)
Starting thickness of 6 mm
Starting diameters of 4
Death zone at the surface, this dead zone is
dependant on the inspected wall thickness
Some geometries are impossible (has to be
reviewed case by case)
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THANK YOU
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