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EMAT Application on Incoloy furnace Tubing
By
Ramamohan Reddy M(ASNT Level III –UT, PCN Level III –UT,PAUT&TOFD)
NDT CCS
1. Introduction – EMAT2. EMAT- Ultrasound waves3. EMAT-Surface waves4. EMAT-Guided Wave (MRUT)5. MRUT Axial Scan6. MRUT- Circumferential scan7. EMAT MRUT Vs Conventional LRUT8. Most probable Furnace tube failures9. Furnace Tube inspection challenges10. NDT Techniques for Furnace tube inspection11. EMAT guided wave application on Incoloy tubing12. Data interpretation13. Advantages of EMAT- MRUT 14. Limitation of EMAT-MRUT15. Conclusion
Outlines
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Introduction
• EMAT or Electro Magnetic Acoustic Transducer is an Ultrasonic Testing (UT)
technique that generates the sound in the part inspected instead of the
piezoelectric transducer.
• This Abstract briefs about EMAT-Guided waves will be Utilized to inspect furnace
tube for any In-service defects such as corrosion , pitting , Erosion etc
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Introduction- EMAT
• In Conventional UT ultrasound will be generated by piezoelectric transducer and then it will send to part to be inspected with help of couplant .
• In EMAT, ultrasound will be generated in the part itself using magnetic field and Lorentz force.
• EMAT is Non contact technique and doesn’t requires coupling medium.
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EMAT- Ultrasound Waves
• EMAT Shear Vertical waves will be used for
weld inspection as like piezoelectric
generated ultrasound
• EMAT Guided waves will be used for detecting
corrosion, Pitting's , Erosion etc as like LRUT .
EMAT Guided wave testing also called as MRUT
• In Typical EMAT inspection, ultrasonic shear
vertical, Guided Wave in medium Range,
Longitudinal and shear Horizontal wave
utilized
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EMAT- Ultrasound Waves
• EMAT Longitudinal waves will be
used for Thickness measurements
as like piezoelectric generated
ultrasound, especially for boiler
tubes and high temperature spot
thickness measurement up to 800
deg C
• EMAT Shear Horizontal waves will
be used for austenitic steel welds
inspection . It is not easy to
generate Shear horizontal waves
with piezoelectric transducers
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EMAT – Surface Waves
• EMAT Surface waves are much stronger than piezoelectric generated
surface waves. Also Wide band surface wave generation is possible with
EMAT which will allow more coverage and detection
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Characteristics:
• Detects cracks, pits and corrosion on pipes and tanks
• Axial scan provides full volumetric inspection of pipelines (including under supports) at fast inspection speeds (150mm/s)
• Circumferential scan permits inspection of supports and soil interfaces up to 1.8 m deep
• In tank configuration, the system scans up to 1m per pass
• Custom scanner adapts to all configurations and can inspect in any orientation (horizontal, up, down or sideways)
EMAT-Guided Waves (MRUT)
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Axial Scan
• The Sensor travels axially
straddling the OD of the pipe
• Transmitter sends Lamb waves
around the pipe in both
directions
• The receiver detects the sound,
measuring the amplitude loss
and/or change in time of flight
• 360º Scan of pipe with speed of
approximately 150mm per
second
• Ideal for diameters between 6”
(150mm) and 24” (600mm)
MRUT – Axial Scan
provides two different inspection types :
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Corroded Wall
T R
No Corrosion
T R
Time
Time
Am
pli
tud
eA
mp
litu
de
MRUT Axial Scan
• Corroded walls cause Time-Of-Flight shifts and decreases in amplitude
• Time-Of-Flight shifts are caused by velocity changes when traveling
through the thinner portion of the pipe
• Decreases in amplitude are caused by energy loss reflected from corroded
areas
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Circumferential Scan
• Used mainly for soil-to-air
interface and under pipe
supports
• Scanning performed normally
using S1 Lamb Wave mode
• Transmit/ Receive sensors
travel circumferentially around
the pipe
• Sensors configured in pulse-
echo will detect reflections
from defects along the line
• Specially designed sensor can
send sound only in one
direction using two channel
systems
• Signal can be normalized for
auto-calibration in P/C mode
MRUT – Circumferential scan
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MRUT Circumferential Scan
• Pitch-catch or pulse-echo method
• Reflection form an indication will come later in the time domain
Corroded Wall
T R
No Corrosion
T R
Time
Time
Am
pli
tud
eA
mp
litu
de
Signal directly from
transmitter used for
normalization
Reflection from the
indication
EMAT MRUT Vs Conventional LRUT
LRUT MRUT
Wave form Guided Waves Guided waves and Shear horizontal waves through volume
Sensitivity 10% of cross-sectional area wall loss
10 times sensitive than LRUT
Frequency Low and fixed User define depends on application
Detection Limited to corrosion and metal loss
can detect cracks as well
Sound orientation Sound direction will be axial
Can be axial and circumferential
Distance It can travel tens of meters It can travel maximum 2.5meter
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Most probable Furnace tube failures
Tube failures associated with combination of multiple mechanisms as below
• Creep: It is a generally slow developing form of degradation occurring in metals under stress and higher pressures
• Carburization: It typically occurs when furnace firing is increased to compensate for a heavy coke deposit on the ID of the tube
• Oxidation: happen when temperatures exceed design maximums
• Erosion• Low toughness
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Furnace tube inspection - Challenges
• It is very difficult to send /penetrate the ultrasound especially in incoloy furnace tubes due its high nicle content
• Complete tube is not accessible , only partial tube is accessible for inspection
• All deterioration mechanisms cause in Inner dia of tube
• Very tough work environment due to closed area hence it is very difficult for continuous stay inside the furnace
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NDT Techniques for Furnace tube inspection
1. Corrosion Mapping ( UT): It is possible to take manual
reading from suspected locations, but it is not
possible to inspect whole tubes due to restricted
access and time .
2. LRUT: It is not possible to place the LRUT probe set
around the tube due to restricted access. Though it
fits there will be high attenuation and noise causes
from material(Incoloy 800) since guided waves travels
in axial direction.
3. EMAT-Guided Wave: It is very much possible and
works very fine since guided wave will generates in
part itself. It will be discussed in detail .NDT CCS
EMAT guided waves application on IncoloyFurnace tubes
• Conventionally to inspect furnace tubes made of incoloy 800 series are
inspected by Eddy Current Technique externally wherever tube area
accessible using crawler technique.
• However with this technique the area unable to reach by Eddy current
probe are not inspected.
• In other hand using ECT internally could be an option, although higher
diameter ECT is challenge task and limited to straight portions.
• By using EMAT of guided wave Medium Range Ultrasonic Testing (MRUT)
the area tubes inspected reliably comparably fast to ECT as well as the area
not reachable by ECT externally.
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Data Interpretation
• There will reflections from discontinues
which has to be marked as suspected
location
• Also there will be loss of signal
amplitude if no reflections from
discontinuity.
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Advantages of EMAT- Guided Wave
• It doesn’t required couplant
• Very fast screening technique
• Surface finishing is not required like piezoelectric UT
• Works till 1mm coating and coating thickness need not to count as like
piezoelectric UT.
• EMAT-Guided waves are sensitive than Long range guided waves
• Frequency of the guided waves will be user defined at required sensitivity
level
• Excellent tool for multi directional discontinuities.
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Limitations of EMAT- Guided Wave
1. It is only screening tool hence backup UT requires to quantify .
2. Heavy coating and metal coating leads to a lot confusion to
interpret results.
3. Materials must be conductive to generate ultrasound with EMAT.
4. It requires high power source
5. Sensors are bigger than Piezoelectric transducers, so it will be
difficult to inspect tubes <1” in diameter
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Conclusion
Conventional ECT is considered as an option for furnace tube inspection either by
scanning externally through a crawler or possibly by internal bobbin technique.
However ECT has limitation for few inaccessible areas while scanning externally
and challenges in bend area while scanning internally. EMAT with MRUT is
considered fast better effective method comparably with ECT performed
externally in addition to reach full circumference of tubes. Also cleaning is not a
vital requirement as comparable to ECT and resolution is better than LRUT
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Any Questions?
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