ULTRASONIC TESTING

PROCEDURE : ASME BPVC SEC V ARTICLE-4 & 5 [4 – weld, 5 – Raw material]

ACCEPTANCE: ASME BPVC SEC VIII DIV-1 APPENDIX-12

INTRODUCTION:

 It is one of the NDT method.

 To find surface, sub surface & Internal level defect by using ultrasonic sound.
 There is no material & thickness limitation.
 We can find thickness of the material.
 We can find length, depth & size of the defect, but cannot find shape of the defect.
 Hint: 0.1 to 5 MHz probes are used in UT.

PRINCIPLE :

 Acoustic Impedance (or) Change in velocity.

 It describes how much resistance an ultrasonic sound encounters as it passes through a
material.
Z = 𝝆v

Acoustic Impedance = Density x Velocity

= Mass x distance
Volume time
= gram x m
m3 s
Z = g/m2s

Sound Frequency:

Below 20 Hz Infrasonic (or) Sub sonic [Not audiable] (ex: Earth quake)

20 Hz to 20000 Hz Sonic [Audiable]

Above 20000 Hz Ultrasonic sound [Not audiable] (ex: Dolphin, bats sounds)

ADVANTAGE :

 Immediately Result.
 No material and thickness limitation.
 High sensitive.
 No Health Hazard.
 Portable Equipment.
 We can find length, depth, size of the defect.
DISADVANTAGE :

 Initial cost is High.

 Highly skilled labour required.
 Technical oriented.
 Doesn’t find shape of the defect.

Sound:

 Sound is like a wave in a medium vibration particles travel by a one medium to another medium.
 Sound travel by any medium except vacuum.

Characteristics of waves:

 Frequency [F] Hz (Hertz)

 Wave length [⋋] mm (Milli meter)
 Amplitude [A] dB (Decibel)
 Velocity [V] m/s (Meter per second)

Frequency:

Number of waves (or) Number of cycle (or)

Number of vibration produced per second.

Wave length:

 The distance for one complete cycle.

 The distance between crust to crust (or)
thrust to thrust.
 Frequency is inversely proportional to wave length.

⋋=V/F

Velocity:

The maximum distance travelled by a wave per sec.

Amplitude:

 The maximum distance moved by a particle

in vertical direction.
 Either positive (or) negative.
 Amplitude (or) sound loudness measured in dB.
Velocity Table

Material Longitudinal velocity (m/s) Shear wave (m/s)

Air 330 m/s -

Water 1480 m/s -

Oil 1440 m/s -

Perpex 2730 m/s 1430 m/s

Steel 5920 m/s 3250 m/s

Aluminum 6300 m/s 3130 m/s

Stainless steel 5740 m/s 3120 m/s

Types of waves:

Longitudinal wave
Primary wave
Shear wave
Surface wave
Secondary wave
Plate wave

Longitudinal wave:
 It is otherwise called as “Compressional wave”.
 The particle vibration parallel to the sound wave.
 Velocity is high, so wave length & penetration is also is high.
 Attenivation is low.
 It can travel in solid, liquid & gas.

Longitudinal wave = Elasticity

Density

Shear wave:

 It is otherwise called as “Transverse wave”.

 The particle vibration perpendicular to the sound wave.
 Velocity is low, so wave length & penetration is also is low.
 Attenivation is high.
 It travel only in solids because gas, liquid & Air has no rigidity.
 Shear wave = Rigidity
Density
Surface wave:

 It is otherwise called as “Rayleigh wave”.

 Particle vibration Elliptical to the sound wave.
 Penetration = 1⋋.
 Very high sensitivity.
 Reflect from sharp edges, finger print.
 Travel in solid & high density medium.
 Velocity of surface wave is 40% of longitudinal wave & 60% shear wave.

Plate wave:

 It is otherwise called as “Lamp wave”.

 Particle vibration Elliptical to the sound wave.

Couplant:

 Couplant is a liquid substance used between the probe face and the test surface materials.
 It is used to increase the Transmission co-efficient & helps to remove air gap.
Eg: water, starch, glycerin, oil, etc…

Properties of good couplant:

 It should not affect the test material.

 It should increase the transmission co-efficient.
 It has ability to function under temperature range of 5° C - 55° C.
 It should be easily removable from the surface.
 It should spread easily on the surface.
 Easily available & Non toxic.

Boundary of physics:

(Without perpex )
θi θr Air gap

Steel θi = Angle of incident

θr = Angle of reflection

Oblique wave:

Θi θr Θi = Angle of incident

θRL θr = Angle of reflection

θRS θRL = Angle of Refraction (Longitudinal)

θRS = Angle of Refraction (Shear)

when sound at an angle interface below action,

Reflection

Refraction

Mode conversion ( A change in wave form from one to another )

First Critical Angle:

At which angle refracted longitudinal wave reach surface level or 90° is called first critical angle.

Second Critical Angle:

At which angle refracted Shear wave reach surface level or 90° is called Second critical angle.

Snell’s Law:

It states that relation between incident & refraction angle.

Sin θi = Vi
Sin θR VR

Where,

Θi = Angle of incident

θr = Angle of refraction

Vi = Velocity of incident medium

VR = Velocity of refracted medium

 High Frequency Amplitude Attenivation Sensitivity

Low Wave length Velocity Penetration

Low Frequency Amplitude Attenivation Sensitivity

High Wave length Velocity Penetration

Conclusion:

 Probe which having 45°, 60°, 70° are mostly used.

 35°, 80° probes are rarely used because their incident angle closed to critical angle (so the probe only
used for pipe)

Generation of Ultrasonic wave:

1) Piezo electric method

2) Magneto strictive method
3) Electro dynamic method
4) Thermal extitation method

Piezo electric method is used in NDT field. Because very compact method.

Types of piezo electric method:

 Piezo electric method

 Inverse piezo electric method

Piezo electric method:

Electric energy converted into Mechanical energy (Due to crystal vibration)

Inverse Piezo electric method:

Mechanical energy converted into Electrical energy.

Transmitter:

 The electric energy converted into mechanical energy.

 Electric energy given to crystal vibration at high frequency.
 Wave transmitted into the material.

Receiver:

 Mechanical energy converted into electrical energy.

 Reflected sound wave is received (or) catch up by the crystal to produce current.
 Ultrasonic wave converted into electric energy and it produced a echo at a CRT screen in flaw detector.

Piezo electric crystal:

 The piezo electric crystal placed inside the probe and it produce ultrasonic sound.
 Crystal made up of Synthetic material.
 Piezo electric crystal having high curie point.
 Crystal thickness is inversely proportional to the frequency ( T ↑ F↓ ) ( T ↓F ↑ )
 Crystal diameter is directly proportional to the frequency ( D ↑ F↑ ) ( D↓ F↓ )

Types of crystal:

 Natural crystal
 Artificial crystal

Natural crystal:

Natural crystal generally found on earth. Eg: Quartz, Rockwell salt.

Advantage:

It high curie point (600°C)

Disadvantage:

Poor transmission and receiver

Artificial crystal:

1) Barium titanate [ Ba ti O3 ]
2) Lithium sulphate [Li So4 ]
3) Lead Zinconate titanate [Pb Zr Tio3 ]
4) Lead metal niomate [ Pb Nb2 O6 ]
Crystal Transmitter Receiver Transmitter & Receiver Curie point
Quartz Poor Poor Poor 600°C
Barium titanate Good Poor Fair 120°C
Lithium sulphate Poor Good Fair 75°C
Lead zinconate titanate Fair Fair Good 320°C
Lead metal niomate Good Good Good 570°C

Beam profile:

Dead Zone:

 Crystal ringing time.

 The initial echo masking defect echo.
 The crystal unable to receive the sound vibration because if transmitting the sound wave.
 We cannot identify the defect in this zone.
 Frequency inversely proportional to dead zone.

( F ↑ dz ↓ ) ( F ↓ dz ↑ )

Near zone: (or) Fresnel zone

 The distance (or) Region (or) Zone immediately front

of the transducer.
 The Beam (or) the wave doesn’t spread in this region.
 We cannot find defect in this zone.
 In this zone sound intensity (or) fluction variation high
due to the Constructive (or) Destructive interference.

1) Near zone is directly proportional to frequency [ F ∝ N ]

(F↑N ↑) ( F↓N↓)

2) Diameter is directly proportional to Near zone [ D ∝ N ]

(D↑N ↑) ( D↓N↓)

3) Wave length is inversely proportional to Near zone [⋋ ∝ 1/N ]

(⋋↑ N ↓ ) ( ⋋↓N↑)

𝐃𝟐 𝐃𝟐𝐅
Near zone N = N=
𝟒⋋ 𝟒𝐕
Fare Zone: (or) Fraunhofer zone

 This Region in beyond the near zone.

 Ultrasonic sound wave spread in this zone.
 Crystal diameter is inversely proportional to fare zone [D ∝ 1/F ]

(D↑F ↓) ( D↓F↑)

𝐒𝐢𝐧 𝛉 𝟏.𝟐𝟐⋋
Beam spread =
𝟐 𝐃

4 MHz 2 MHz
F↑ F↓ Frequency
D↓ D↑ Dead zone
NZ ↑ NZ ↓ Near zone
FZ ↓ FZ ↑ Fare zone
Types of probes:

1) Normal probe
2) TR probe
3) Angle probe
4) Delay line probe
5) Immersion probe
6) TOFD (Time of flight diffraction probe)
7) PAUT (Phase array ultrasonic testing)
8) CCP (Counter correction probe)
1 ) Normal probe:

 0° probe, single crystal probe, straight beam probe, Longitudinal wave probe, linear probe.
 It produces longitudinal wave (or) compressional wave.
 It has a 0° crystal working with piezo electric method.
 The initial echo should be on CRT screen. [CRT = Cathode Ray Tube]

Advantage:

High penetration

Disadvantage:

Dead zone & Near zone will be high

2 ) Angle probe:

 It produce longitudinal wave due to mode conversion it converted into shear wave.
 It has single crystal at an angle.
 The initial echo should be shown on CRT screen.
 Dead zone, Near zone is medium.
 This probe is available 35°, 45°, 60°, 70°, 80°.

Uses:

Mostly used for weld scanning

Size 8x9 mm, 14x14 mm

3 ) TR probe:

 It produce longitudinal wave.

 It has dual crystal at an angle (5° - 12°).
 Initial echo will not shown in CRT screen.
 Dead zone, Near zone is below.
 This probe is possible for 3 to 25 mm job thickness.

3 ) Delay line probe:

 It produce longitudinal wave.

 No Dead zone and Near zone.
 Initial echo will be out of CRT screen.
 Low penetration, so used for finding low job thickness.(6 mm thickness)

Types of scanning:

1) A-scan
2) B-scan
3) C-scan
4) D-scan
5) P-scan

1 ) A-Scan

 We can find length and depth of the defect.

 In this type of scan, mostly used in NDT field.
2 ) B-scan:

 It has shows Cross sectional view (or) Side view.

 We can find depth of the defect.
 We cannot find length of the defect.

3 ) C-scan:

 It has shows Top view.

 We can find length of the defect.
 We cannot find depth of the defect widely used in medical field.

4 ) D-scan:

 Cross sectional view and Top view shown in this scan.

 Used in advanced types of UT (TOFD used in this type of scan).
 We can find length & depth of the defect.

5 ) P-scan:

 Combination of all scanning this type mostly used in advanced ultrasonic testing.

Types of scanning Techniques:

1) Pulse echo technique

2) Pitch catch technique
3) Through transmission technique
4) Angle probe technique
5) Tandom technique
6) Immersion technique
7) Resonance technique
8) PAUT
9) TOFD

1 ) Pulse echo technique:

 Crystal vibrates in pulse echo technique.

 Crystal electrically powered transmit ultrasonic sound into the specimen.
 When the electrical energy stop the crystal, receivers the reflected sound energy either defect (or)
back surface of the specimen.

2 ) Pitch catch technique: (Dual angle probe)

 In this technique two angle probe are used same frequency same crystal size.
 One is transmitter another one is receiver, we cannot find depth of the defect.
Uses:

 Used to identify Root level defect.

 Used to find the transfer correction.

3 ) Through transmission technique:

 It is a old technique.
 Two 0° probe keep opposite each other, two side access needed.
 One Transmitter and another is Receiver.
 We cannot find the depth of the defect.
 Defect is smaller than crystal diameter back wall echo will be loss.
 Defect is larger than crystal back wall echo will shown.

Uses:

 Test bonding between two materials.

4 ) Angle probe technique:

 In this technique normally used weld scanning.

 Using 45°, 60°, 70° probe, Frequency 2 MHz, 4 MHz

Skip distance:

½ skip distance = waves through Root

Full skip distance = waves through Roof

Uses:

 Weld scanning

5 ) Tandom technique:
  In this technique two angle probe used same angle, same frequency, same side.
 One Transmitter and another Receiver.
Pitch catch Tandom
Echo shown No repair Repair
No echo Repair No repair
6 ) Immersion technique: Probe Opposite side Same side
 25 MHz frequency probe used.
 The probe fixes manipulator and immersed into the water. [Manipulator = Automatic system
operated]
 Mostly low thickness materials are used.

7 ) Resonance technique: (Use Pipe)

 We used continuous echo, condition of wave length should be multiplies of it’s material.
 The fundamental of resonance F = V/2t
 In this technique mainly use full to measure of plate thickness, sheet bonding material.

CALIBRATION:

To check equipment is working properly with know standard.

Standard calibration block:

IIW = International Institute of welding

IOW = Institute of welding

ASTM = American Society of testing material

ALCA = Aluminum Company of America

Checking of V1 Block (or) A2 Block (or) Dutch Block (or) Armature Block (or) IIW Block:

1) Horizontal Linearity Checking

2) Vertical Linearity Checking
3) Sensitivity Checking
4) Resolution Checking
5) Near Zone & Fare Zone Checking
6) Penetration Checking (or) Perpex Checking
 Index Point Checking
 Probe Angle Checking

1 ) Horizontal Linearity Checking:

𝐑𝐚𝐧𝐠𝐞
Major Scale =
𝟏𝟎

𝐌𝐚𝐣𝐨𝐫 𝐬𝐜𝐚𝐥𝐞
Minor Scale =
𝟓

 To check Time (or) Distance base

2 ) Vertical Linearity Checking:

6 dB drop 50%
12 dB drop 100%

𝐇𝟐
dB = 20 log
𝐇𝟏

 To check Amplitude of an equipment

3 ) Sensitivity Checking:
 Ability to find small size of defect.
4 ) Resolution Checking:
 The ability of equipment to distinguish two (or) more than echo from the defects at same point
(or) Close together.
5 ) Near Zone & Fare Zone Checking:
6 ) Perpex Checking:
Perpex longitudinal velocity = 2730 m/s
Thickness = 23.5 mm
Diameter = Ø 50 mm
Index point checking:
To check center point of sound beam where it leaks
the probe center in the material.
Probe angle checking:
Probe angle thickness = ± 2°
To check the probe angle standard distance.
Checking of V2 Block (or) A4 Block (or) kidney Block:

1) Horizontal Linearity Checking

2) Vertical Linearity Checking
3) Sensitivity Checking
4) Index Point Checking

5) Probe Angle Checking

V1 block (Add +125) V2 block (Add +75)

25 Radius 100 Radius 25 Radius 50 Radius
1st echo 25 1st echo 100 1st echo 25 1st echo 50
2nd echo 50 2nd echo 225 2nd echo 100 2nd echo 125
3rd echo 75 3rd echo 350 3rd echo 175 3rd echo 200
REFERENCE BLOCK:

1. Area Amplitude Block

2. Distance Amplitude Block
3. Step Block (or) Step wedge
4. Flat Bottom Hole Block
5. Notch Block

1 ) Area Amplitude Block:

It provides standard for discontinuities with same depth and different size.

2 ) Distance Amplitude Block:

It provides standard for discontinuities with same depth and different size.

3 ) Step Block:
4 ) Flat Bottom Hole Block:

5 ) Notch Block:

MAJOR STEPS [UT NORMAL PROBE]:

Visual testing

Probe selection (Frequency & Size)

Range selection

Calibration (V1, V2)

Scanning dB

Length, depth, size of the defect

Accept / Not accept

Visual Testing:

 Surface preparation [Grinding, dust, rust, impurities removed]

 Paint removed.
 Temperature [5°C – 55°C]
 Light intensity [1076 LUX]
 Information about the material.
Probe selection:

As per ASME BPVC Sec V Article 4 & 5

Below 25 mm – TR probe
Above 25 mm – Normal probe
Frequency Crystal Size
As per ASME BPVC Sec V Article 4 & 5
Below 25 mm – 4 MHz Ø 10 Ø 10
Above 25 mm – 2MHz 4 MHz 2 MHz
AWS D1.1 Structural code for steel Ø 24 Ø 24
Any thickness – 2 to 2.5 MHz
Range selection:

Range = 2 x Job Thickness

𝐑𝐚𝐧𝐠𝐞
Major Scale =
𝟏𝟎

𝐌𝐚𝐣𝐨𝐫 𝐬𝐜𝐚𝐥𝐞
Minor Scale =
𝟓
Calibration:

No of Echo = Range . No of Echo = Range .

V1 block thickness V2 block thickness
Sensitivity checking
Ability of the equipments to defect the small size defect (Ø1.5 mm)
1 ) RAW MATERIAL DEFECT:
 Lamination
 Inclusion
Lamination:
 It is defined as flat and thin sub surface separation present inside the metal plate.
 Complete loss of thickness back wall echos multiple echo from defect.
Inclusion:
 Foreign material trapped inside the material is called inclusion.(Slag of oxide and other
substance)
2 ) SERVICE INDUCED DEFECT:
 Corrosion
 Erosion
 Pitting
Corrosion:

 It is chemical (or) Electro chemical reaction between a material.

 Job thickness is damaged up to half of it’s thickness.

Erosion:

 It is loss of material due to flow of fluid.

 Gradual corrosion of material.

Pitting:

 Group of corrosion is called pitting.

 Corrosion which forms holes.

MAJOR STEPS [UT ANGLE PROBE]:

Visual testing

Probe selection (Frequency & Size)

Range selection

Calibration (V1, V2)

DAC from reference block

Transfer correction dB

Scanning dB

Length, depth, size of the defect

Accept / Not accept

Visual Testing:

Same as normal probe.

Probe angle selection :

As per ASME BPVC Sec V Article 4 & 5

Method -1 Method-2 (plate) Method -3(pipe)

6-25mm 70° θ= 90°-t Sin θ=[1-2t/D]
25-35mm 60° θ=angle of probe T=job thickness
Above 35mm 45° t=thickness of job D=diameter of pipe

As per AWS D1.1

Up to 38mm 70°

Above 38mm 60°, 45°

Frequency Crystal Size

As per ASME
Up to 25 mm – 4 MHz 8x9 8x9
Above 25 mm – 2MHz 4 MHz 2 MHz
As per AWS 14 x 14 14 x 14
Any thickness – 2 to 2.5 MHz
Range selection:
Range = 2t / Cos θ

Skip distance:

½ skip distance = t x tan θ

Full skip distance = 2t x tan θ

Beam path (or) Skip path:

½ skip beam path = t / Cos θ

Full beam path = 2t / Cos θ

Surface distance:

Surface distance = Beam path x sin θ

Depth of defect:

Depth (½ skip) = BP x Cos θ

Depth (Full skip) = 2t – BP x Cos θ

Depth (1 ½ skip) = BP x Cos θ – [2t]

Depth (2 skip) = [4t] – BP x Cos θ

Depth (2 ½ skip) = BP x Cos θ – [4t]

Beam path (or) Skip path:

The travelled distance between beam entry point and point of reflection from the defect.

Surface distance:

The horizontal distance between the beam exit point to the defect location is called surface distance.

Skip distance:

The horizontal distance between the beam entry point and the center of the weld is called skip distance.

Calibration:

With V1 & V2 blocks and do all other calibration.

DAC – Distance amplitude correction curve:

Definition:

 To evaluate the unknown defect by known defect by using reference block.

 To evaluate the defect indication curve using holes at same size and different depth using reference
block (DAC Block)
 The reference block should be the same material as be material be examination.
 To evaluate the unknown defect by reference of known defect from reference block.’

Steps:

 The probe is placed on a reference block catch the high peak of SDH (side drilled hole) at 80% mark the
point and note down the dB (reference dB).
 Catch the another high peak of another SDH hole and mark the 2nd point without changes in reference
dB.
 Catch the another high peak from the next SDH hole mark the 3rd point without any changes in
reference dB.
Reference block thickness selection:

Weld job thickness (T in mm) Reference block thickness in mm Hole diameter (Ø) in mm
6 mm – 25 mm 19 mm Ø 2.5 mm
26 mm – 50 mm 38 mm Ø 3 mm
51 mm – 100 mm 75 mm Ø 5 mm
Above 100 mm Thickness + 25 mm ( + 1.5 mm)

Note:

To each increased of weld thickness (50 mm) over 100 mm job thickness the hole diameter should be
increase 1.5 mm.

SDH – Side drilled hole

Reference block
DAC block
SDM block

DAC Curve in CRT Screen:

1st Point – Below the job thickness

2nd Point – Above the job thickness

3rd Point – Double of the job thickness

Reference level 80% - Not acceptable

Reference level 40% (6 dB) - Recording level

Reference level 16% (14 dB) - Evaluation level

Problem: 1

Job thickness 20 mm, How to choose Probe angle, frequency and Reference block?

Job thickness T = 20 mm Angle θ = 70° Frequency F = 4MHz

2𝑡 2 𝑥 20
Range = =
𝑐𝑜𝑠𝜃 𝑐𝑜𝑠70°

Range = 116 mm

½ skip distance = t x tan θ Full skip distance = 2t x tan θ

= 20 x tan 70° = 2(20) x tan 70°

= 54 mm = 109 mm
 Reference Block:

Reference block = 19 mm Ø = 2.5 mm

19 mm block

¼ 0.25 x 19 = 4.75

½ 0.5 x 19 = 9.5

¾ 0.75 x 19 = 14.25 1st Point – Below the job thickness

1 ¼ 1.25 x 19 = 23.75 2nd Point – Above the job thickness

1½ 1.5 x 19 = 28.5

1¾ 1.75 x 19 = 33.25

2¼ 2.25 x 19 = 42.75 3rd Point – Double of the job thickness

2½ 2.5 x 19 = 47.5

2¾ 2.75 x 19 = 52.25

Thickness = 14.25

Beam path = t / Cos θ Surface distance = BP x Sin θ

45° 60° 70°
= 14.25 / Cos 70° = 41.66 x Sin 70° Sin θ 0.71 0.87 0.94
Cos θ 0.71 0.5 0.34
BP = 41.66 SD = 39.14 tan θ 1 1.73 2.75

Thickness = 23.75

Beam path = t / Cos θ Surface distance = BP x Sin θ

= 23.75 / Cos 70° = 69.44 x Sin 70°

BP = 69.44 SD = 65.25

Thickness = 42.75

Beam path = t / Cos θ Surface distance = BP x Sin θ

= 42.75 / Cos 70° = 124.99 x Sin 70°

BP = 124.99 SD = 117.4
Problem: 2

Job thickness 40 mm, How to choose Probe angle, frequency and Reference block?

Job thickness T = 40 mm Angle θ = 45° Frequency F = 2MHz

2𝑡 2 𝑥 40
Range = =
𝑐𝑜𝑠𝜃 𝑐𝑜𝑠45°

Range = 113 mm

½ skip distance = t x tan θ Full skip distance = 2t x tan θ

= 40 x tan 45° = 2(40) x tan 45°

= 40 mm = 80 mm

Reference block = 38 mm Ø = 3 mm

19 mm block

¼ 0.25 x 38 = 9.5

½ 0.5 x 38 = 19

¾ 0.75 x 38 = 28.5 1st Point – Below the job thickness

1 ¼ 1.25 x 38 = 47.5 2nd Point – Above the job thickness

1½ 1.5 x 38 = 57

1¾ 1.75 x 38 = 66.5

2¼ 2.25 x 38 = 85.5 3rd Point – Double of the job thickness

2½ 2.5 x 38 = 95

2¾ 2.75 x 38 = 104.5

Thickness = 28.5

Beam path = t / Cos θ Surface distance = BP x Sin θ

45° 60° 70°
= 28.5 / Cos 45° = 40.30x Sin 45° Sin θ 0.71 0.87 0.94
Cos θ 0.71 0.5 0.34
BP = 40.30 SD = 28.5 tan θ 1 1.73 2.75
Thickness = 47.5

Beam path = t / Cos θ Surface distance = BP x Sin θ

= 47.5 / Cos 45° = 67.17 x Sin 45°

BP = 67.17 SD = 47.5

Thickness = 85.5

Beam path = t / Cos θ Surface distance = BP x Sin θ

= 85.5 / Cos 45° = 120.91 x Sin 45°

BP = 120.91 SD = 85.50

Problem: 3

Job thickness 60 mm, How to choose Probe angle, frequency and Reference block?

Job thickness T = 60 mm Angle θ = 45° Frequency F = 2MHz

2𝑡 2 𝑥 60
Range = =
𝑐𝑜𝑠𝜃 𝑐𝑜𝑠45°

Range = 169.70 mm

½ skip distance = t x tan θ Full skip distance = 2t x tan θ

= 60 x tan 45° = 2(60) x tan 45°

= 60 mm = 120 mm

Reference block = 75 mm Ø = 5 mm
19 mm block
¼ 0.25 x 75 = 18.75
½ 0.5 x 75 = 37.5
¾ 0.75 x 75 = 56.25 1st Point – Below the job thickness
1 ¼ 1.25 x 75 = 93.75 2nd Point – Above the job thickness
1½ 1.5 x 75 = 112.5
1¾ 1.75 x 75 = 131.25 3rd Point – Double of the job thickness
2¼ 2.25 x 75 = 168.75
2½ 2.5 x 75 = 187.5
2¾ 2.75 x 75 = 206.25
Thickness = 56.25
Beam path = t / Cos θ Surface distance = BP x Sin θ
45° 60° 70°
= 56.25 / Cos 45° = 79.54x Sin 45° Sin θ 0.71 0.87 0.94
Cos θ 0.71 0.5 0.34
BP = 79.54 SD = 56.25 tan θ 1 1.73 2.75

Thickness = 93.75

Beam path = t / Cos θ Surface distance = BP x Sin θ

= 93.75 / Cos 45° = 132.58 x Sin 45°

BP = 132.58 SD = 93.74

Thickness = 131.25

Beam path = t / Cos θ Surface distance = BP x Sin θ

= 131.25 / Cos 45° = 185.61 x Sin 45°

BP = 185.61 SD = 131.25

Transfer correction dB:

 The reference block material having smooth surface and having low sound loss.
 The test material having different grain structure and sound loss will be varied.
 So, we need the transfer correction dB.

Steps:

 Two angle probe with same size, same frequency, same angle is taken one is transmitter and another
one is receiver.
 Probe placed over the reference block using pitch catch technique catch the high peak and set at 80%
FSH (First Screen Height) and note down the dB.
 Now repeat the same process on the test material, catch the high peak set it 80% of FSH and note
down the dB.
 The different between those dB are due to sound loss. This is transfer correction dB.

Scanning Level:

Scanning Level = Reference dB + Transfer correction dB + Scanning dB (6-14 dB) As per ASME.

 If any defect is found the scanning dB should be reduced before the defect should be evaluate.
Scanning Pattern:

1. Lateral Scan
2. Swivel Scan (or) Rotational Scan
3. Transverse Scan (or) Depth Scan
4. Orbital Scan

1 ) Lateral Scan:

 Move the probe up side and down side.

 It is used to identify length of the defect.

2 ) Swivel Scan (or) Rotational Scan:

 We can swivel probe from same place at 10° angle.

 To find the high peak of the finded echo.

3 ) Transverse Scan (or) Depth Scan:

 We can move the probe forward and backward.

 To find at the depth of the defect.

4 ) Orbital Scan:

 It is used of finding defect parallel to the defect.

 We cannot find the parallel defect using other types of scanning pattern.
 Using orbital scan we can find it from same place to radius of the weld.
 Orbital scan is best for the transverse defects.

UT – ACCEPTANCE CRETERIA:

Planner: (or) Linear Indication

Planner Not acceptable any regardless of length. (Crack, LOF, LOP, Cluster of porosity)

Non Planner: (or) Rounded Indication

(Inch – in, Thickness – t)

¼ in (6 mm) for‘t’ up ¾ in (19 mm)

1 2
[ t] For‘t’ ¾ in to 4 in (19 mm to 57 mm) Acceptance Limit
3

¾ in (19 mm) for‘t’ over 2 ¼ in above (57mm) Defect Job

Thickness Thickness
6 mm 19 mm
1 19 to 57 mm
t
3
19 mm Above 57 mm