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Reduction of backwall echo by more than 12 dB. Indications from discontinuities frequently invisible.

Reason: spongy shrinkage, gas holes, inclusions or large inclined discontinuity.

△/ > D_f

where

D_f is the sound-beam diameter;

Д/ is the dimension of the discontinuity.

Key

Д77 Reduction of backwall echo

^a Echo height

^b Probe movement

^c Echo dynamics

^d A-scan

— Reduction of backwall echo by more than 12 dB, measurable dimension of indication range

Typical indication:

Individual indication, half-value dimension Д/ smaller than or equal to the sound-beam diameter D_F.

Key

/ Lateral extension of indication

H Maximum echo height of individual indication

^a Echo height

^b Probe movement

^c Echo dynamics

^d A-scan

— Individual indication without measurable dimension

s

Typical indication:

Individual indication, half-value dimension A<7 equal to or less than sound-beam diameter D_T at reflection point.

Key

d Dimension of indication in through-wall direction

H Maximum echo height of individual indication

^a Echo height

^b Probe movement

^c Echo dynamics

^e A-scan

— Individual indication without measurable dimensions; individual indication with one measurable dimension parallel to the test surface and without measurable dimension in through-wall direction

b

Typical indication:

Individual indication(s), mainly in the same position in through-wall direction.

Dimension of indication range larger than the sound-beam diameter D_f.

Key

I Lateral extension of indication

А/ Half-value dimension of indication

Яі, H₂ Last maximum echo heights on opposite sides of indication

^a Echo height

^b Probe movement

^c Echo dynamics

^d A-scan

— Individual indication with measurable dimensions: measurable length, non-measurable width; measurable length, measurable width

Typical indication:

Clustering of indications, mainly resolvable with non-measurable dimensions.

Dimension of indication range equal to or larger than the sound-beam diameter D_f.

Key

/ Lateral extension of indication

Л/ Half-value dimension of indication

H-і, H₂ Last maximum echo heights on opposite sides of indication

^a Echo height

^b Probe movement

^c Echo dynamics

^d A-scan

d

As

1 2

Typical indication:

Individual echo with pronounced echo dynamics only in through-wall direction (travelling indication), or both in through-wall direction and parallel to the test surface:

t = A.s x cos a

where

t is the dimension in through-wall direction;

M is the difference of sound paths from position 2 to position 1;

a is the angle of incidence.

Key

1. Probe position 1

2. Probe position 2

ЛН Reduction of maximum echo height of indication

^a Echo height

^b Probe movement

^c Echo dynamics

^d A-scan

T

b

a

ypical indication:

Numerous individual indications.

During probe movement the sound paths change, but all indications remain without measurable dimensions.

E

Key a b c d

cho height Probe movement Echo dynamics A-scan

Figure B.8 — Numerous individual indications without measurable dimensions but with measurable dimensions of the indication range

Typical indication:

Individual indications with measurable dimensions mainly in the through-wall direction:

/ - A.S X COS ft

where

t is the dimension of the indication range in through-wall direction;

As is the difference of sound paths from position 2 and position 1;

ct is the angle of incidence.

Key

1. Probe position 1

2 Probe position 2

AH Reduction of maximum echo height of indication

^a Echo height

^b Probe movement

^c Echo dynamics

^d A-scan

Typical indication:

Group of indications, mainly non-resolvable individual indication. Dimension of indication range equal to or larger than sound-beam diameter D_f.

This type of indication should only be evaluated if, due to geometrical reasons, a back-wall echo cannot be ob­tained.

A simultaneous reduction of backwall echo should be evaluated in accordance with Figure B.2.

Key

I Lateral extension of indication

Л/ Half-value dimension of indication

D_r sound-beam diameter

/7i, H₂ Last maximum echo heights on opposite sides of indication

Echo height Probe movement Echo dynamics A-scan

Typical indication:

Group of mainly non-resolvable indications:

t - s x cos cr

where

t is the dimension of the indication range in through-wall direction;

Av is the difference of sound paths from position 2 and position 1;

a is the angle of incidence.

Key

1. Probe position 1

2. Probe position 2

4/7 Reduction of maximum echo height of indication

^a Echo height

^b Probe movement

^c Echo dynamics

^d A-scan

Figure B.11 — Group of non-resolvable indications with measurable dimensions of indication range
(angle probe)

Bibliography

[1 ] EN 473, Mon destructive testing-— Qualification and certification of NOT personnel -— General principles.

2. EN 1330-4, Non-destructive testing ■— Terminology — Part 4: Terms used in ultrasonic testing.

3. EN 1370, Founding . Surface roughness inspection by visualtactile comparators.

4. EN 1559-2, Founding -— Technical conditions of delivery ■— Part 2: Additional requirements for steel cast­

ings.