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For discontinuity detection, the gain shall be increased until the noise level becomes visible on the screen (search sensitivity).

The echo heights of the flat-bottomed holes given in Table 2 or of the equivalent side-drilled holes shall be at least 40 % of the screen height at the end of the thickness range to be tested.

If, during examination, suspicion arises that the reduction of backwall echo indication exceeds the recordable value (see Table 3), testing shall be repeated using locally reduced test sensitivity and the reduction of backwall echo indication shall be determined quantitatively in decibels.

The sensitivity setting of angle-beam probes shall be such that the typical dynamic echo pattern of these reflectors (see Figure 3) is clearly visible on the screen.

NOTE It is recommended that the sensitivity setting of angle-beam probes is verified on real (not artificial) planar disconti­nuities (cracks with dimensions in through-wall direction) or on walls perpendicular to the surface and infinite to the sound beam. In these circumstances, the probe shoe should be contured to fit the casting shape (see EN 583-2).

The following types of indications can occur separately or jointly during the examination of castings and shall be observed and evaluated:

• reductions of backwall echo which are not due to the casting shape or the coupling;

• echo indications of discontinuities.

The reduction of backwall echo is expressed in decibels as the drop of the backwall echo height. The height of the echo indication is given as flat-bottomed or side-drilled hole diameter.

Unless otherwise specified, all back wall echo reductions or echo heights reaching or exceeding the levels given in Table 3 shall be recorded.

When using transverse wave probes, irrespective of amplitude, all indications which display travelling charac­teristics or have an apparent dimension in through-wall direction shall be recorded for subsequent assessment ac­cording to 5.5.7.2.

Each location where indications to be recorded have been found shall be marked and indicated in the test report. The location of reflection points shall be documented, e.g. by sketch or by photograph.

The locations where indications to be recorded have been found (see 5.5.5) shall be investigated more closely with respect to their type, shape, size and position. This investigation can be achieved by altering the ultrasonic test technique (e.g. changing the angle of incidence) or by additionally carrying out radiographic examination.

For characterization and sizing of discontinuities see EN 583-5.

The ultrasonic determination of the dimensions of a discontinuity with an accuracy sufficient for engineering appli­cations is only possible under certain preconditions (e.g. knowledge of the type of discontinuity, simple geometry of the discontinuity and optimum impact of the sound beam on the discontinuity).

The characterization of the type of discontinuities can be improved by using additional sound directions and angles of incidence. For simplification of the procedure, the following categorizations of discontinuities are made:

• discontinuities without measurable dimensions (point discontinuities);

• discontinuities with measurable dimensions (complex discontinuities).

NOTE 1 Annex A gives information on sound-beam diameters in order to distinguish between discontinuities with or without measurable dimensions.

NOTE 2 Annex В gives information on types of indications and on the determination of their dimensions. It also gives infor­mation on range setting (see 5.5.2) and on sensitivity setting (see 5.5.3).

NOTE 3 For the determination of the dimensions of discontinuities, it is recommended that probes having a sound-beam diameter as small as possible at the location of the discontinuity are used.

The boundaries of any discontinuity shall be defined by the perimeter line at which the signal amplitude falls to 6 dB below the last maximum or at which, in the case of backwall echo reduction, the echo is reduced by 6 dB (2 MHz probe) below the height of the undisturbed backwall echo.

NOTE The dimension in through-wall direction of the discontinuity should be measured according to Figure 4.

The sizing of planar discontinuities and their assessment in relation to specified severity levels shall be carried out by the probe movement according to 5.5.7.1, but in this case, the echo is reduced by 20 dB (see Figure 3).

The examination report shall contain at least the following information:

• reference to this European Standard (EN 12680-1);

• characteristic data of the examined casting;

• extent of examination;

• type of examination equipment used;

• probes used;

• the examination technique with reference to the examination area;

• all data necessary for sensitivity setting;

• information on all characteristic features of discontinuities to be recorded (e.g. backwall echo reduction, posi­tion and dimension in through-wall direction, length, area and flat-bottomed hole diameter) and the description of their position (sketch or photograph);

date of the examination and name of the responsible person.EN 12680-1:2003 (E)

Table 1 — Acceptance limits for volumetric discontinuities

ваі thicknesses not greater than 50 mm, flat-bottomed holes exceeding 8 mm diameter are unacceptable.

eat thicknesses greater than 50 mm, the acceptability of flat-bottomed holes exceeding 8 mm diameter in the rim zone shall be agreed between the manufacturer and the purchaser.

^s in core zone and rim zone.

• todcattufe less than 25 mm apart shall be considered as one discontinuity.

* t ndcaton in the core zone is caused by an individual reflector the thickness of which does not exceed 10% of the wal thickness, (e.g. centreline shrinkage), then, in case of severity took 2 io 4. values 50 % higher than those specified in this table, are acceptable and in case of severity level 5, no limit is specified.

13Table 2 — Ultrasonic testability requirements t

Dimensions in millimetres

Table 3 — Recording levels

^a Formula for converting the flat-bottomed hole diameter into the side-drilled hole diameter, see note to 5.2.

Key

2. Severity level 2

3. Severity level 3

4. Severity level 4

5. Severity level 5

^a Largest acceptable individual indication area in square millimetres

^b Distance from test surface in millimetres

Indications with measurable dimensions are not permissible as severity level 1.

Figure 1 — Acceptance limits for individual planar indications mainly orientated
in through-wall direction, detected with angle probes

Key

1. Rim zone

2. Core zone

t Wall thickness

^at/3 (max. 30 mm)

Figure 2 — Division of wall section into zones

b) Uninterrupted reflector

Key

d Dimension in through-wall direction

5i, s₂ Length of the sound-beam path

t Thickness

a Angle of the incidence

Echo height

d = (s₂ - si) x cos a

Figure 3 — Measurement of the dimension of discontinuities in through-wall direction

Key

^a Scanning position "A"

^b Scanning position "B"

^c А-scan from scanning position "A"

^e А-scan from scanning position "B"

Depth extension d = t - (si + s₂) where

t is the wall thickness;

5i, s₂ are the lengths of the sound-beam paths.

Figure 4 — Measurement of the dimension of discontinuities in through-wall direction
with normal probes

Annex A
(informative)

Sound-beam diameters

Annex A gives information on sound-beam diameters in order to distinguish between discontinuities with or without measurable dimensions.

Sound-beam diameter (- 6 dB) in millimetres

Sound-beam path in millimetres

Figure A.1 — Sound-beam diameters according to sound-beam path and near-field length
for various probes

The near-field length and the sound-beam diameter can be calculated using the following formulae:

D²

N = -=±- (A.1)

4хД where

N is the near-field length in millimetres;

D_c is the crystal diameter in millimetres;

Л is the wave length in millimetres;

s is the sound-beam path in millimetres;

D_f is the sound-beam diameter, in millimetres, along the sound-beam path, where the decrease of the sound pressure perpendicular to the central beam is 6 dB.Annex В

(informative)

Types of indications

Figures B.1 to B.11 show possible distinctions between the different types of indications by echo-dynamics.

For the identification of the type of indication, the test sensitivities can be changed according to:

• the distance from the surface to be examined;

• the geometrical shape;

the surface finish of the surface to be examined.

Key

1. Range setting, e.g. with calibration block in accordance with EN 12223 or EN 27963

2. Check of test equipment on side-drilled hole of calibration block, echo height of side-drilled hole 100% of

screen height

3. Sensitivity setting in an area of the casting to be examined, free from discontinuities without reference reflector

4. Average height of noise level approximately 5 % to 10 % of screen height

5. Check of test sensitivity and test equipment by observation of the echo-dynamics of an as-cast surface in through-wall direction

6. A-scan

7. Typical echo dynamic

^a Echo height

^b Probe movement

^c Echo dynamics

^d As-cast surface

Typical indication: