advance inspection ultrasonic inspection

ADVANCE ULTRASONIC INSPECTION

DACON INSPECTION SERVICES

TUBE INSPECTION PSEC vs. MFL & NFT

Who we are

Conventional and Advanced NDT and Inspection Services

Oil and Gas, Refinery, Petrochemical, Heavy Industry, Mining

Over 400 personnel including more than 300 inspectors

Thailand headquarters with International expertise since 1979

DACON INSPECTION SERVICES F O R A L L Y O U R I N S P E C T I O N N E E D S

PSEC vs. MFL and NFT

Focus during this work shop will be on PSEC and how it compares to the other available techniques. • Partial Saturation Eddy Current

• Dacon’s preferred technique for fin/fan tubes and in some cases normal CS tubes

• Magnetic Flux Leakage

• His

• Near Field Testing

• Only been on the market in recent years.


Partial Saturation Eddy Current

Theory

• Probe contains normal eddy current coils

• In addition the probe contains 2 coils that are used as electro magnet

• The electro magnet in the PSEC probe is used to partly cancel out the magnetic properties of the material

• The electro magnets field is mainly active

at the inner surface of the tube material Compensates the skin effect Some eddy currents can penetrate

the material

• Defects will cause a change in permeability and in amount of eddy currents in that location

• The impedance of the test coil will be affected by a combination of changes in permeability and eddy current strength

• Signals that represent the impedance of the test coil and thus the condition of the tube are presented on a computer screen


Advantages

• Possible to examine carbon steel (finned) tubes

• Both pits and overall wall-loss can be detected (diam. pits > 2 mm)

• Sizing of internal defects possible

(phase information)

• Possible to distinguish between internal and external defects

• Non volumetric defects like cracks

can be detected depending on size, shape and orientation

• Defects under support plates can be

detected and to some extent quantified

Disadvantages • Sizing of external defects limited

(based on signal volume)

• Cleaning of tubes very critical because use of big fill factor probe required

Partial Saturation Eddy Current Advantages & Disadvantages


Magnetic Flux Leakage (MFL)

Theory

• Probe contains permanent magnets which are used to form a magnetic field in the tube wall

• Defects will influence the path of the magnetic field and will cause some of flux to leak out of tube which will be picked up by the coils in the probe

• Wall thinning will increase the density of the magnetic flux lines in the remaining tube wall which is picked up by the hall sensor

• Size of leakage fields depends on pull speed and size, shape, orientation of the defect

• Signals that represent the size of the leakage field and thus the condition of the tube are presented on a computer screen


Advantages

• Fast when used as screening technique


• Both pits and overall wall-loss can be

detected (diam. Pits > 2 mm)

• Possible to distinguish between in-and external defects

• Non volumetric defects like cracks can be

detected depending on size, shape and orientation

• Defects under supports can be detected

and to some extend quantified

Disadvantages • Less suitable as stand alone technique

• Sizing of in- and external defects limited


• Probe speed dependent

• Cleaning of tubes very critical because of high fill factor probe requirement

Magnetic Flux Leakage (MFL) Advantages & Disadvantages


Near Field Testing (NFT)

Theory

In Near Field Testing the pickup coils are located within 0-1.5 tube diameters away from the exciter coils. Within the near field zone the eddy currents generated in the tube wall by the alternating current driven exciter coil create a shielding effect of the exciters flux. As eddy currents propagate through the material’s inner wall, an opposing secondary magnetic flux is developed in the material that attenuates the primary field strength and limits its extension. Logically, the near zone would be the area where there is greatest sensitivity to discontinuities because of the high concentration of magnetic flux.


Advantages

• Fast when used as screening technique


• Both pits and overall wall-loss can be detected (diam. Pits > 3 mm)

• Detection of internal thinning and pitting based on sensitivity of eddy current lift off

• Cleaning of tubes less critical

Near Field Testing (NFT) Advantages & Disadvantages

Disadvantages • Cannot detect external defects

• Sizing defects limited


• Less suitable as stand alone technique


Signals explained

Conventional ET signal Calibration tube 20,40,60,80 %Ext 10 % ID groove


MFL signal calibration tube

Calibration tube 5 mm diam. defects


PSEC signal calibration tube



PSEC signal calibration tube, phase spread



PSEC signal calibration tube, absolute channel

Calibration tube Absolute external 25% 50E (including some external damage) hole 5 mm


PSEC signal finned tube

Finned tube Drilled holes 1.5 mm 2.0 mm 3.0 mm


NFT signal calibration tube

Calibration tube 6.35 mm Diam. Defects


Signal comparison PSEC, MFL, NFT

PSEC 5 mm hole

MFL 5 mm hole

NFT 6.35 mm hole


How Can We Help?

Contact Email : [email protected]

Phone : +66 (0) 33 012 484-7

www.dacon-inspection.com

advance inspection ultrasonic inspection

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