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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