Ut Important

UT IMPORTANT THEORY / NUMERICALS / LOGICS

HIGH LIGHTS

1. Ultrasonic Wave Energy

Energy α Z A2

Energy α

ZA2

– (1)

Energy α

P2

– (2) A = Amplitude

Z P = Pressure of piezoelectric Crystal

Z = Acoustic ImpedanceA = AmplitudeP = Pressure of piezoelectric Crystal

P α ZA – (3)

(Note : Two questions may come from these formulas)

• Elastic force = The force keeps the atoms of a body in a defined pattern• Sound = Vibration transmitted point to point• Sound waves are also called elastic wave or mechanical wave. Related Terms with sound A, E, P, V• Velosity depends on elastic cons. & density (Note : Question may come from this concept)• Frequency of a given sound is always constant

2. Wave Mode

a. Longitudinal / Compressional / Pressure (VL)

In this mode propagation of wave is parallel to the dispersion of automs.

b. Transverse / Shear (VT)

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Only exist in solid, wave propagation perpendicular to this dispersion of atoms.

Polimarisation is possible only in shear wave.

VT ≈ 0.5VL

__________ (4)

3. Surface wave / Reyleigh Wave (VR)• Partical Motion of surface wave is elliptical• As the depth increased the degree of energy decreased drastically.• Penetrates upto one wave length

VR = 0.9 VT ________ (5)

4. Plate Wave / Lamb Wave• This kind of wave is being generated by special method. Better to consult ASM Vol. 17 for details.• This is of two type

• Velosity of plate wave depends on Type of lamb wave Frequency Thickness Elastic constant & Density

Z = VxD _____________ (6)

RE = (Z2-z1)2 _____________ (7)(Z2+z1)2

Medium RE TEWater / Persfex 0.1 0.9

Water / Al 0.7 0.3Water / Steel 0.9 0.1

dB = 20 log10(A2/A1) – (8) ZC

= ZP x Zm

Zc = geometrical means of Zp & ZmZp = Impedance of Probe

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Symmetrical Plate WaveUpsymmetrical Plate Wave


Zm = Impedance of MetalZc = Impedance of Couple

Acoustic Mismatch (Z2-Z1) RE increases

Unit of Z = kg/m2s

[Elastic Arisotropy & Acoustic Arisotropy]

Concept: When layer of couplant is less than λ, the energy loss depends on the layer of couplant.

At couplant thickness λ/4, the maximum transmission is taken placeAt couplant thickness λ/2, the minimum transmission is taken place

SNELL’S LAW

Sinθ1=

Sinθ2

9

V1 V2

1. Concept of Critical Angle

Condition - (1) Longitudinal wave generates in the probe which in the second media (material to be tented) produces two different wave mode (VL & Vs)

Condition - (2)

θc1 is called 1st Critical Angle

ie.

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Sinθc1=

Sin900

VL1 VL2


Condition - (3)

θc2 is called 2nd Critical Angle

Ie.

i

When V2 > V1 beam will be DIVERGED in second media

i

When V2 < V1 beam will be DIVERGED in second media

Concept of lensed probe (Mainly used in Immersion Testing)

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Sinθci =V1

10V2

Sinθc2=

Sin900

VL1 VL2

Sinθc2 =V1

11V2

F =•• R X VL (LENSE)

12

VL – VW

(Water)


OFF-SET DISTANCE FINDING METHOD

AB = DOA = D/2 = RAC = MN = OFFSET DISTANCE = X

Pto 13 Photo 13

Sinθ AC=

XOA R

ie.

Again,

OR

OR

OR

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n = • VL (LENSE)13

VL – VW

(Water)

f =•

Rn

14n – 1

X= Sinθ 15 R

Sinθ=

Sinr

VW VM

Sinθ =VW

X Sinr

16VM

X=

Sinr

R VM

x = RVW

Sinr

17VM


xm = focal spot in metal

(Convergent beam with greater refraction angle)

18 Fw = Focal Length in water xw

= Water path

19 Nm = Near filed in metal Nw = Near Field in water

COME BACK TO LIMITED ANGLE (θ)

20

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xm = Fw-XwVW

VM

Nm = (Nw–Xm)X

VW

VM

Sinθ =IDOD

Sinθ =IDOD

=OD-2T

OD

= 1 - 2TOD

or,= 1 -

2TOD

T = Thickness of pipei.e., ID = OD-2T

Focal spot in water

(Incase metal piece is not placed inside water; focal point distance was FW)


Again

VLM = longitudinal Velocity in WaterVTM = Transverse Velocity in Hollowbar inside the water.

or

IMMERSION METHOD

Minimum water path = 1/4t + ½” of water when the immersed material is steel.

Acoustic Lense:

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or, T = (Sinθ –

1) X

OD21

2

Sinθ =x XID OD/2

Sinθ =2x •

22OD

Sinθ=

SinrLW VTM

Sinθ =

SinrVLW

23VTM

Min. water path =

Material Thickne

ss X

Vw 24

VM


Come Back to Snell’s Law:

ie.

An example based on eqn. 25

• Incase sound travels 10mm in water, what will be the equivalent traveling distance in steel.

So, Dist. Steel =

PHASE REVERSAL

If Z2 < Z1 RP is –ve & this is called phase reversal.

When Z2 < Z1 Wall is called Soft wall When Z1 < Z2 this is called Hard wall

Phase Reversal takes place in soft wall condition

Radiofrequency (RF)

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Sinθ1=

Sinθ2 = Velosity = Dist. (Thk) X TimeV1 V2

Or time = Velosity Thickness

VLW=

VL Steel25

Dist (W) Dist. Steel

VL Water

=VL Steel

10 Dist. Steel

10 XVL Steel

mmVL Water

10X6.0 mm

•

= 40 mm1.5

RP =Z2 –

Z1Z2 +

Z1

Z1 •

• wallZ2


Hard Wall

Soft Wall (Phase Reversal)

Passage through material

Pure Absorption Due to 1. Elastic Hystarasis 2. Thermal Condition 3. Internal Friction

Loss of Energy

Loss of Energy due to scatter at grain boundary Energy α e-(αa x) (1)

Loss of energy at scatter Energy α e-(αe - αs)x (2)

Adding (1) & (2)

Energy & e-(αa + αs)x (αa + αs) = attenuation coefficient x = distance

(with distance increase, sensitivity decrease)

26

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Sinθ/2 1.22 λD


27

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N =D2

4λ


0

1 2

Note: f2 – f1 = Band Width

28

Amplitude α D2 (D=Probe Dia)

Important ConceptAmplitude α

1Dist2

GIVE ATTENTION TO FOLLOWING IMPORTANT CONCEPTS

E λ P R S DZ

N BS

SPEED

FREQUENCY DIA OF PROBE

Note:E λ P R S D

ZN B

SENERGY

Wave length

Penetratio

n

Scatter at Grain Boundary

Sensitivity

Dead Zone

Near Zone

Beam Spread

• Scatter (λ) ↑ Grain Size ↑• Damping ↑ Pulse Lengh Pulse Energy • Due to damping pulse energy decreases and band width increases• Pulse width to half of the wave length is called the maximum damping• Highly damped probes called broad band probe

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Quality factor (QF)

=f0

f2 – f1


• Very high damped probes called sock wave probe.

• Damping ↑ QF • Roof angle of TR probe ↑ dead zone effective range • TR probe has better signal to Noice Ratio• QF ↑ Penetration ↑• For coarse Grain Higher Dampened probe Required• Broad Band Beam Required Broad Beam amplifier• Tighter or narrow beam probe is giving better lateral resolution• Higher the damping better depth resolution. Therefore broad band will have small pulse

length and provide better depth resolution• In shock wave probe, Dead zone is very less (about 2mm only), shock wave probe is very

high damping probe & best for surface resolution• Delay block is having better near surface resolution• Higher damping shorter the pulse duration, shorter the dead zone. Higher the damping,

Higher the band width and lower the QF, lower the dead zone, lower the pulse duration.

GENERATION OF PULSE

1. Magnetostriction (40/50 kpsi)

2. EAMT probe

No need to touch the job

3. Phase Array

Photo

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4. Piezo electric effectPiezo electric effect Defecting ultrasound

Photo

QUARTS CLASICFICATION

1) Lithium Sulphate2) Barium Titanate & Lead Zirconate Titanate > Ceramic Crystal

USING OF CERAMIC CRYSTAL

Ceramic crystals are made by powder metallurgy process. After the shaping of barium Titanate and leas zinconate Titanate, the are gone through a high pressure and high temperature & under a high electric field. This is called polling. Therfore by poling the crystals are oriented in manner as per the figure. In an effect during the application of pressure they can contract & expand in longitudinal direction.

In case they are not going through poling, the crystals are not kept in such manner and as a result during the application of pressure (current), the expansion of different crystal particles will be in different direction and ultimately there shall not be any generation of pulse.

Photo

This vibration is called the fundamental frequency if Ø > 10t at fundamental frequency

then t = λ / 2 29

l =4λ = 30

2

n = 1, 2, 3, 4, 5….

When n = 1, this is fundamental frequency & when n is other than l, it is called harmonic

tC =λ

=Vc

312 2fc

Vc = Velosity of sound in crystal material.

1. Through Transmission

Max. intensity at fundamental frequency. Now a days it is trying to make all the probes at its natural frequency.

t= n

λ2

f1 = V

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n • 322t

f2 =

(n+1)

v

• 332t

Photo

2. Resonance

Resonance method used for the measurement even for low thickness other application of this method is to check the bounding condition.

3. Pulse Echo (**)

Pulse Repetitions Rate – It PRR is very high, ghost echo may appear (PRR, PRF)

Photo

PRR CALCULATION (IMMERSION TEST)

The reflected beam should be arrest by the probe.

Vel =DistanceTime

Formula (36) is for one pulse but generally minimum 3 pulse on interrogation are required. Therefore the modified formula is:

Note : n = No of Pulses

Again go back to clause 3 (**) above;

In order to avoid ghost echo next pulse should come after dying of the first echo.

Time between pulses velocity

=

DistanceTime

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Vscan =Ø + d

34

time

Time =1 35

PRR

Vscan = (Ø + d)

* PRR

36

Time =(Ø + d) PRR 37

n


Vm = 2 x thk job38

Time

T = 2 x n x tjob 39

Vm

Next Signal should appear after ‘n’ echo taken place

T = 2 x n x tjob 40

Vm

PRR = Vm41

2 x n x tjob

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Internal Mode Conversion

Internal Mode conversion

PHOTO

PHOTO

PHOTO

So for root crack 600 probe should not be used but for lack of side wall fusion 600 probe is ideal.

Beam profile of normal beam probe

PHOTO

Sound goes all the where due to interference

Constructive Interference at the nature axis

Beam profile is result of sound interference

Probe should have highest sensitivity at the centre

Transmission zone roughly two times the near zone

Beam profile

Sin r/2 = K. λ42

D

OR

Sin r/2 = K. V job43

D DC fc

At Near Field zone sensitivity is less as the location & size identification is critical.

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PHOTO

DGS (Dis. Gain, size) is a multiple DAG Curve.

In DGS, only FBH are used whereas in DAC SDH, notches, FBH are used.

In FBH 1mm = 20% then 2mm = 80%

but in SDH, no formula exists. Only we can say instead of 1 mm in 2 mm amplitude will be increased.

dB = 20log A1 43A2

PHOTO

dB Ration2 1.25 : 16 2 : 120 6 : 126 19.9 : 144 158:160 1000:1

Why TR probe is not having any initial Echo

PHOTO In Normal Beam initial pulse is going directly to amplifier and also going from normal beam. Due to its one part directly transfer to amplifier, initial pulse is appearing

PHOTO But as per the second figure in TR probe, no pulse can go directly to the amplifier. It has to go through Transmitter to job to Receiver to Amplifier. That is the reason there is no initial echo.

PHOTO

PHOTO

PHOTO

PHOTOAt position (1) which is the second multiple echo from the delay block and in that position no defect

When a separate circuit produce current in phase & out phase, it changes the damping characteristic. When it is in phase with probe frequency, it shortend the probe length or it increases the pulse

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height and the probe is dampenedWhen it is in reverse phase, it shortened the pulse heightPHOTO Max. height at fundamental frequencyPHOTO When it is dampened, Broad band

results with low quality frequencyPHOTO Delay BackPHOTO Delay ThicknessPHOTO

At position (1) which is the second multiple echo from the delay block and in that position no defect from the job is detectable, that is the reason delay blocks are used for a specific thickness which is turn classified as equivalent thickness of material.

Reflector plate Echo Technique

For thin plate & composite section

PHOTO PHOTO

In immension test, contour surface deliver broad pulses, therefore for better result focused probes should be used during scanning of countour surfaces.

Paint Brush probe or Linear Mosaic probe

When multiple probes are in a line, this is called paint Brush probe / Mosaic probe.

THE CONFIGURATION OF A MOSAIC PROBE

PHOTO

“Mosaic” for a known area to be tested.

SCANNING SPEED CALCULATION (For Plate)

PHOTO W = Width of the plateL = Length

So area scanned / see = s x w Total area = L x W

Time = L x WS x W

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PHOTO Case 1PHOTO Case 2PHOTOPHOTO

Countour connection lesnse where the countour of the probe is equal to the curvature of the pipe.This is also a countour corrective probeThis is a focusing probeLine focusing probe


Effective scan area = Probe area – overlap So, W = Probe Ø – overlap

SCANNING SPEED CALCULATION (BAR / TUBE)

PHOTO Circumference Speed(Sc) =

∏ x D x RPM

Linear Scanning Speed (Sl) =

W x RPM

W = Scanning Index = (Probe Diameter Overlap)

Time Taken (T)

=

S47

L

A-SCAN

PHOTO

• Synchronizer Circuit also called Timer Circuit / Clock Circuit. It controls the PRR• Pulser – It gives a higher voltage pulse to the probe (-ve voltage). Voltage Range used before pulser to

delay next voltage.• Sweep circuit – Range control is on the sweep circuit.• Receiver

PHOTOPHOTOPHOTORejects cut off equal heights from all echos.

AMPLIFIER BAND WIDTH

The range of frequency a amplifier can control is called Amplifier Band with.

Amplifier Band width – Narrow Band (2-4 Mhz)Amplifier Band width – Broad Band (0.5-4 Mhz)

Note: Amplifier width control is on the amplifier site & not change the probe frequency.

Broad band amplifier should use with the broad band width probe.

DYNAMIC RANGE OF DISPLAY

Ratio of defects that can be presented on the CRT called Dynamic Range of Display.

dB control helps to increase the dynamic range of display.

MONITER CIRCUIT / GATE CIRCUIT

To selectively monitor the part of the CRT and this is called Gating. Therefore two controls are the Gate start control or Gate Central Control

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Gate width

Gate threshold – It is a gate of ampude. Any defect amplitude beyond threshold will not make audiosound.

Node Error

PHOTO On amplification the cut of is shifted, this is called nodal error. In order to avoid nodal error, M/s. Should be calibrated on the peak of the amplitude.

(Detail of other connections to pulser in A-Scan system)

In A-Scan Amplifier connected to vertical plate & sweep Generator is connected to Horizondal.

PRR circuit may be separate or the part of clock / synchronizer.

B-Scan

PHOTO Sweep circuit is connected to vertical axis. Therefore in B-Scan only sweep line will be shown

X PositionSensor shows the position of the probe on x axis

PHOTO

PHOTO So B-Scanning gives the depth & size along the scanning direction.

PHOTO PHOTO

PHOTO PHOTO

PHTO

Good depth information may be possible on latest m/s with multiple gating x and color coding.

C scan also called P-Scan

Scanning angle consideration during scan from a Taper Surface

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