EMAT Application on Incoloy furnace Tubing By Ramamohan Reddy M (ASNT Level III UT, PCN Level III UT,PAUT&TOFD)
Outlines 1. Introduction EMAT 2. EMAT- Ultrasound waves 3. EMAT-Surface waves 4. EMAT-Guided Wave (MRUT) 5. MRUT Axial Scan 6. MRUT- Circumferential scan 7. EMAT MRUT Vs Conventional LRUT 8. Most probable Furnace tube failures 9. Furnace Tube inspection challenges 10. NDT Techniques for Furnace tube inspection 11. EMAT guided wave application on Incoloy tubing 12. Data interpretation 13. Advantages of EMAT- MRUT 14. Limitation of EMAT-MRUT 15. Conclusion
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
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.
EMAT- Ultrasound Waves In Typical EMAT inspection, ultrasonic shear vertical, Guided Wave in medium Range, Longitudinal and shear Horizontal wave utilized 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
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 EMAT- Ultrasound Waves
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
EMAT-Guided Waves (MRUT) 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)
MRUT Axial Scan provides two different inspection types : 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)
Amplitude Amplitude 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 T R No Corrosion Time T R Corroded Wall Time
MRUT Circumferential scan 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 pulseecho 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
Amplitude Amplitude MRUT Circumferential Scan Pitch-catch or pulse-echo method Reflection form an indication will come later in the time domain T R Signal directly from transmitter used for normalization No Corrosion Time T R Reflection from the indication Corroded Wall Time
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 Sound orientation Limited to corrosion and metal loss Sound direction will be axial can detect cracks as well Can be axial and circumferential Distance It can travel tens of meters It can travel maximum 2.5meter
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
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
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.
EMAT guided waves application on Incoloy Furnace 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.
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.
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.
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
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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