nde formula

7/29/2019 nde formula

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Formulas for Ultrasonic Nondestructive Testing

Ultrasonic Key

V = velocity

Sin = sine of angle

Cos = cosine of angle

F = frequency

D = diameter of the transducer

BS = beam spread

= lambda or wavelentgh

p = density of the material

Z = acoustic impedance

dB = decible

NF = near field

Snell's Law:

Sin 1 / Sin 2 = V1 / V2 or Sin 2 = (Sin 1 * V2) / V1

Near Field:

NF = D2F / 4V or NF = D2 / 4

Beam's Spread:

BS = K * (V/DF) Note: K = 1.22 for 0 or null point K = 0.7 for 6 dB down

Wave Length:

= V/F

Acoustic Impedance:

Z = pV


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Coefficient of Reflection:

((Z1 - Z2)2 / (Z1 + Z2)2)1/2

Decibel Ratio:

dB difference = 20 log10 (amplitude1 / amplitude2)

Flaw Location Depth:

Depth = cos of the angle X the sound path

Flaw Location from the exit point (surface difference):

Surface = Sound path X Sin of the angle

Formulas for Radiography Nondestructive Testing

Radiography Key

I = intensity

D = distance

Ug = geometric unsharpness

F = focal spot size

D = distance from the source to the source side of the object ( Unsharpness )

T = the thickness of the object plus the distance from the object to the film

SSD = source to the detector (film) distance

Inverse Square Law:

I1 / I2 = D22 / D12 or I2 = I1 * D12 / D22

Unsharpness:

Ug = FT / D

Source to Detector Distance:

SDD = (FT / Ug) + T


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To figure the strength of a source after a certain amount of time:

If a Ir. 192 source is 120 days old that is 1.6 half lives. So if the source was 100 curies at

purchase the strength at 120 days is 39.6 curies.

100 * 0.51.6

= 39.6

If you have a 1/2" of lead and the half value layer is 0.2" you have 2.5 have value layers.

If you had 60 Roentgens and put the 1/2" of lead at the point of 60 R you would now

have 10.6 R on the opposite side of the lead.

60 * 0.52.5 = 10.6

Formulas for Magnetic Particle Nondestructive Testing

Magnetic Particle Key

N = number of turns in the coil

I = amperes

R = radius of the coil

L - is the usable length for the exam Ex. 9" each side of the center coil would allow for a max. length of18"

All formulas are for American units of measurement.

Testing with part next to the inside wall of the coil:

NI = 45000 / (L / D) or I = (45000 / (L / D)) / N

Testing with part centered in the coil and less than a 10% fill factor:

NI = (35000R) / ((6L / D) - 5)

Effective Diameter of hollow round parts:

(OD2 - ID2)1/2

Effective Diameter of hollow rectangular parts:

2(At - Ah / P)1/2

At = the area of the total cross section of the part and Ah = the area of the hollow cross section of the part


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1. Wavelengthwhere:

f= frequency

c = acoustic velocity

= wavelength

|wave length|

|frequency|

|velocity|

2. AcousticImpedance

where:

Z = acoustic impedance

c = acoustic velocity

= density of transmitting medium

acoustic

impedance

|acoustic

impedance|

3. Transmission

Coefficient

for Normal

Incidence

where:

Z1= acoustic impedance in medium 1

Z2= acoustic impedance in medium 2

D = transmission coefficient

|transmission

factor

(coefficient) |

4. Reflection

Coefficient

for Normal

Incidence

where:

Z1 = acoustic impedance in medium 1

Z2 = acoustic impedance in medium 2

R= reflection coeffcient

|reflection

coefficient

5. Snell's Lawwhere:

c1= acoustic velocity in medium 1

c2= acoustic velocity in medium 2

1= beam angle in medium 1

2= beam angle in medium 2

Example

|Snell's law|

6. Near Zonewhere:

D = the diameter of a flat circularoscillator

= wavelength of the ultrasound

N = length of near zone

|near field|
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7. Half Angle of

Divergence

(for flat

circular

oscillators)

where:

= half angle of divergence

kdB = constant based on stated dB

drop from center maximum

= wavelength

D = the diameter of a net circularoscillator

Values ofkdB vary for the dB drop that is to

be determined.-1.5dB k=0.37

-3dB k=0.51

-6dB k=0.7-10dB k=0.87

-12dB k=0.93

beamspread

|divergence|

8. Convergence

PointFor determining thefocal distance of a

focused beam in a 2

media geometry.

where:

fx = new focal distance

f1 = focal distance in coupling

medium

c1= acoustic velocity in couplingmedium

c2= acoustic velocity in second

medium

P1= pathlength in the coupling

medium

|convergence

point|

|focused

beam|

9. Sound Pressurewhere:

= density

c = velocity of sound

= angular frequency

= particle displacement

Z = c = acoustic impedance

normally in units of N/m2

|acoustic

power

density|

10. Intensity of

Acoustic

Power

where:

p = pressure

= angular frequency

= particle displacement

Z = c = acoustic impedancenormally in units of W/m2
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11. Intensity Level

B = 10 log

(J/Jo)

where:

Jo is the arbitrary (10-12 W/m2)

reference level corresponding to the

faintest sound detectable by the ear.

Since J is proportional to the soundpressure squared, the differencebetween two intensity levels can be

determined by;

normally units are in deciBells(abbr.dB)

12. Attenuationwhere:

po and p are sound pressures at the

start and end of a length d.

alpha is the coeffcient of attenuationfor a given material

alternatively;

normally units of attenuation are in dB and

the attenuation coeffcient is in dB per unit

length

|attenuation

coefficient|

|decibel (dB)|
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