SIST EN ISO 16811:2025

SLOVENSKI STANDARD
01-junij-2025
Neporušitvene preiskave - Ultrazvočne preiskave - Občutljivost in območje
nastavitve (ISO 16811:2025)
Non-destructive testing - Ultrasonic testing - Sensitivity and range setting (ISO
16811:2025)
Zerstörungsfreie Prüfung - Ultraschallprüfung - Empfindlichkeits- und
Entfernungsjustierung (ISO 16811:2025)
Essais non destructifs - Contrôle par ultrasons - Réglage de la sensibilité et de la base
de temps (ISO 16811:2025)
Ta slovenski standard je istoveten z: EN ISO 16811:2025
ICS:
19.100 Neporušitveno preskušanje Non-destructive testing
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 16811
EUROPEAN STANDARD
NORME EUROPÉENNE
March 2025
EUROPÄISCHE NORM
ICS 19.100 Supersedes EN ISO 16811:2014
English Version
Non-destructive testing - Ultrasonic testing - Sensitivity
and range setting (ISO 16811:2025)
Essais non destructifs - Contrôle par ultrasons - Zerstörungsfreie Prüfung - Ultraschallprüfung -
Réglage de la sensibilité et de la base de temps (ISO Empfindlichkeits- und Entfernungsjustierung (ISO
16811:2025) 16811:2025)
This European Standard was approved by CEN on 23 February 2025.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2025 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 16811:2025 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 16811:2025) has been prepared by Technical Committee ISO/TC 135 "Non-
destructive testing" in collaboration with Technical Committee CEN/TC 138 “Non-destructive testing”
the secretariat of which is held by AFNOR.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by September 2025, and conflicting national standards
shall be withdrawn at the latest by September 2025.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN ISO 16811:2014.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 16811:2025 has been approved by CEN as EN ISO 16811:2025 without any modification.

International
Standard
ISO 16811
Second edition
Non-destructive testing —
2025-03
Ultrasonic testing — Sensitivity and
range setting
Essais non destructifs — Contrôle par ultrasons — Réglage de la
sensibilité et de la base de temps
Reference number
ISO 16811:2025(en) © ISO 2025
ISO 16811:2025(en)
© ISO 2025
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO 16811:2025(en)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Quantities and symbols . 1
5 Qualification of personnel . 3
6 Test equipment . 3
6.1 Instrument .3
6.2 Probes .3
6.2.1 General .3
6.2.2 Probe selection.3
6.2.3 Frequency and dimensions of transducer .4
6.2.4 Dead zone .4
6.2.5 Damping .4
6.2.6 Focusing probes .4
6.3 Coupling media .4
6.4 Standard blocks .5
6.5 Reference blocks .5
6.6 Specific test blocks .6
7 Categories of test objects . 6
8 Test objects, reference blocks and reference reflectors . 6
9 Probes . 9
9.1 General .9
9.2 Longitudinally curved probes .10
9.2.1 Convex scanning surface .10
9.2.2 Concave scanning surface .10
9.3 Transversely curved probes .10
9.3.1 Convex scanning surface .10
9.3.2 Concave scanning surface .11
10 Determination of probe index point and beam angle .11
10.1 General .11
10.2 Flat angle-beam probes .11
10.2.1 Calibration block technique .11
10.2.2 Reference block technique .11
10.3 Angle-beam probes curved longitudinally .11
10.3.1 Mechanical determination . .11
10.3.2 Reference block technique . 13
10.4 Angle-beam probes curved transversely. 13
10.4.1 Mechanical determination . 13
10.4.2 Reference block technique .14
10.5 Probes curved in two directions . 15
10.6 Probes for use on materials other than non-alloy steel . 15
11 Time base setting .15
11.1 General . 15
11.2 Reference blocks and reference reflectors .16
11.3 Straight-beam probes .16
11.3.1 Single-reflector technique .16
11.3.2 Multiple-reflector technique .16
11.4 Angle-beam probes .17

iii
ISO 16811:2025(en)
11.4.1 Radius technique .17
11.4.2 Straight-beam probe technique .17
11.4.3 Reference block technique .17
11.4.4 Contoured probes .17
11.5 Alternative range settings for angle-beam probes .17
11.5.1 Flat surfaces .17
11.5.2 Curved surfaces .18
12 Sensitivity setting and echo height evaluation . 19
12.1 General .19
12.2 Angle of incidence . 20
12.3 Distance-amplitude curve (DAC) technique . 20
12.3.1 Reference blocks . 20
12.3.2 Preparation of a distance-amplitude curve .21
12.3.3 Evaluation of signals using a distance-amplitude curve . 22
12.3.4 Evaluation of signals using a reference height . 22
12.4 Distance-gain-size (DGS) technique. 23
12.4.1 General . 23
12.4.2 Reference blocks . 25
12.4.3 Use of DGS diagrams . 26
12.4.4 Restrictions on use of the DGS technique due to geometry . 28
12.5 Transfer correction . 28
12.5.1 General . 28
12.5.2 Fixed path length technique . 29
12.5.3 Comparative technique . 29
12.5.4 Compensation for local variations in transfer correction . 30
Annex A (informative) Determination of sound path distance and angle of incidence in category
2 test objects . .31
Annex B (informative) General DGS diagram .36
Annex C (informative) Determination of contact transfer correction factors .38
Bibliography . 41

iv
ISO 16811:2025(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 135, Non-destructive testing, Subcommittee
SC 3, Ultrasonic testing, in collaboration with the European Committee for Standardization (CEN) Technical
Committee CEN/TC 138 Non-destructive testing, in accordance with the Agreement on technical cooperation
between ISO and CEN (Vienna Agreement).
This second edition cancels and replaces the first edition (ISO 16811:2012), which has been technically
revised.
The main changes are as follows:
— normative references have been updated;
— Annex A and Annex B from the prior edition have been moved to the main text;
— document has been editorially revised.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

v
ISO 16811:2025(en)
Introduction
The following standards on ultrasonic testing are linked:
— ISO 16810, Non-destructive testing — Ultrasonic testing — General principles;
— ISO 16811, Non-destructive testing — Ultrasonic testing — Sensitivity and range setting;
— ISO 16823, Non-destructive testing — Ultrasonic testing — Through transmission technique;
— ISO 16826, Non-destructive testing — Ultrasonic testing — Testing for discontinuities perpendicular to
the surface;
— ISO 16827, Non-destructive testing — Ultrasonic testing — Characterization and sizing of discontinuities;
— ISO 16828, Non-destructive testing — Ultrasonic testing — Time-of-flight diffraction technique as a
method for detection and sizing of discontinuities.

vi
International Standard ISO 16811:2025(en)
Non-destructive testing — Ultrasonic testing — Sensitivity
and range setting
1 Scope
This document specifies the general rules for setting the time-base range and sensitivity (i.e. gain
adjustment) of a manually operated ultrasonic instrument with A-scan display in order that reproducible
determinations can be made of the location and echo height of a reflector.
This document is applicable to contact techniques employing a single probe with either a single transducer
or dual transducers. This document does not apply to the immersion technique and techniques employing
more than one probe.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
1)
ISO 2400, Non-destructive testing — Ultrasonic testing — Specification for calibration block No. 1
ISO 5577, Non-destructive testing — Ultrasonic testing — Vocabulary
1)
ISO 7963, Non-destructive testing — Ultrasonic testing — Specification for calibration block No. 2
ISO 9712, Non-destructive testing — Qualification and certification of NDT personnel
ISO 22232-1, Non-destructive testing — Characterization and verification of ultrasonic test equipment — Part
1: Instruments
ISO 22232-2, Non-destructive testing — Characterization and verification of ultrasonic test equipment — Part
2: Probes
ISO 22232-3, Non-destructive testing — Characterization and verification of ultrasonic test equipment — Part
3: Combined equipment
3 Terms and definitions
For the purpose of this document, the terms and definitions given in ISO 5577 apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
4 Quantities and symbols
A full list of the quantities and symbols used throughout this document is given in Table 1.
1) In the next revision of the standard, the term "calibration block" is intended to be replaced by the term "standard
block".
ISO 16811:2025(en)
Table 1 — Quantities and symbols
Symbol Quantity Unit
A Normalized distance in DGS diagram
A' Probe coordinate mm
a Projected sound path length mm
a' Reduced projected sound path length mm
α Beam angle in steel °
α Beam angle in a non-alloy steel reference block °
r
α Incident angle (beam angle in delay block or wedge) °
d
α Beam angle in test object °
t
β Angle of incidence °
c Sound velocity in reference block m/s
r
c Velocity of transverse waves in test object m/s
t
c Velocity of longitudinal waves in delay block or wedge m/s
d
D Outer diameter of test object or curvature of scanning surface mm
obj
d Wall thickness mm
D Effective transducer size mm
eff
D Equivalent reflector diameter mm
f
D Diameter of spherical-shaped reflector mm
SSH
D Diameter of disc-shaped reflector mm
DSR
D Diameter of probe shoe mm
ps
D Diameter of side-drilled hole mm
SDH
e to e Reference block dimensions mm
1 7
g Depth of contour on probe contact surface mm
G Normalized diameter of disc-shaped reflector in DGS-Diagram
λ Wavelength mm
ΔH Difference between the echo height from a reference reflector and the echo height dB
u
from a discontinuity
l Length of probe shoe mm
ps
l Length of delay path mm
d
Δl Length of contoured probe face mm
ps
N Effective near field length mm
eff
P Reference point at s
r max
P Reference point at s
j j
q Coordinate of reflector mm
s Sound path length (single trip) mm
s Equivalent sound path distance in the delay block
d
s Sound path length of reference reflector mm
j
s Maximum sound path length mm
max
s Sound path length associated with evaluated signal mm
u
s Acoustic equivalent to delay path in test object mm
v
t Depth coordinate of reflector mm
V Gain in DGS diagram dB
V Basic gain dB
j
V Recording gain dB
r
V Gain for determining ΔV dB
t t
ISO 16811:2025(en)
TTabablele 1 1 ((ccoonnttiinnueuedd))
Symbol Quantity Unit
V Indication gain dB
u
ΔV Gain difference dB
ΔV Correction for ΔV dB
~ t
ΔV Gain correction for cylindrical reflector surface dB
k
ΔV Gain difference associated with sound path length dB
s
ΔV Transfer correction (average) dB
t
V Gain for back wall echo on reference block dB
t,r
V Gain for back wall echo on test object dB
t,t
ΔV Difference between indication gain and recording gain dB
u
w Width of probe shoe mm
ps
Δw Width of contouring of the probe face mm
ps
x Distance between probe index point and front edge of probe, for an uncontoured mm
probe
Δx Probe index shift mm
5 Qualification of personnel
a) The testing shall be performed by personnel qualified in accordance with ISO 9712.
b) The requirements for qualification of test personnel shall be specified in the product standards and/or
other applicable documents.
6 Test equipment
6.1 Instrument
The ultrasonic instrument shall fulfil the requirements of ISO 22232-1.
6.2 Probes
6.2.1 General
The probe(s) shall initially fulfil the requirements of ISO 22232-2.
6.2.2 Probe selection
The choice of the probe depends on the purpose of the testing and the requirements of the referencing
standard or specification. It depends on:
— the material thickness, shape and surface condition of the test object;
— the type and metallurgical condition of the material to be tested;
— the type, position and orientation of discontinuities to be detected and assessed.
The probe parameters listed in 6.2.3, 6.2.4 and 6.2.5 shall be considered in relation to the characteristics of
the test object stated above.
ISO 16811:2025(en)
6.2.3 Frequency and dimensions of transducer
The frequency and dimensions of a transducer determine the shape of the sound beam (near field and beam
divergence).
a) The selection shall assure that the characteristics of the beam are the optimum for the testing by a
compromise between the following:
1) the near-field length which shall remain, whenever possible, smaller than the thickness of the
test object.
NOTE It is possible to detect discontinuities in the near field, but their characterization is less accurate and
less reproducible than in the far field.
2) the beam width, which shall be sufficiently small within the test volume furthest from the probe to
maintain an adequate detection level;
3) the beam divergence, which shall be sufficiently large to detect planar discontinuities that are
unfavourably orientated.
b) Apart from the above considerations, the selection of frequency shall take into account the influence of
the sound attenuation in the material and the reflectivity of discontinuities.
The higher the frequency, the greater the test resolution, but the sound waves are more attenuated (or the
spurious signals due to the structure are greater) than with lower frequencies.
The choice of frequency thus represents a compromise between these two factors.
Most ultrasonic tests are performed at frequencies between 1 MHz and 10 MHz.
6.2.4 Dead zone
The choice of the probe shall take into account the influence of the dead zone in relation to the test volume.
6.2.5 Damping
The probe selection shall also include consideration of the damping which influences the axial resolution as
well as the frequency spectrum.
6.2.6 Focusing probes
Focusing probes are mainly used for the detection of small discontinuities and for sizing reflectors.
Their advantages in relation to non-focused single-transducer probes are an increased lateral resolution
and a higher signal-to-noise ratio than with non-focussing probes.
a) Their sound beams shall be described by the focal distance, the focal zone and the width of the focal zone.
b) The sensitivity setting shall be carried out by using reference reflectors.
6.3 Coupling media
a) Different coupling media can be used, but their type shall be compatible with the materials to be tested.
Examples are:
— water, possibly containing an agent, e.g. wetting, anti-freeze, corrosion inhibitor;
— contact paste;
— oil;
— grease;
ISO 16811:2025(en)
— cellulosic paste containing water
b) The characteristics of the coupling medium shall remain constant throughout the verification, the
setting operations and the testing.
c) If the constancy of the characteristics cannot be guaranteed between setting and testing, a transfer
correction may be applied.
One method for determining the necessary correction is described in 12.5.
d) The coupling medium shall be suitable for the temperature range in which it will be used.
e) After testing is completed, the coupling medium shall be removed if its presence will adversely affect
subsequent operations or use of the test object.
6.4 Standard blocks
The blocks used for setting up the ultrasonic test equipment shall be in accordance with those specified in
ISO 2400 and ISO 7963.
The stability of test equipment and setting can be verified by using the blocks given in ISO 2400 and ISO 7963.
6.5 Reference blocks
a) When amplitudes of echoes from the test object are compared with echoes from a reference block,
certain requirements relating to the material, surface condition, geometry and temperature of the block
shall be observed.
b) Where possible, the reference blocks shall be made from a material with acoustic properties which are
within a specified range with respect to the material to be tested and shall have a surface condition
comparable to that of the test object.
c) If these characteristics are not the same, a transfer correction shall be applied.
A method for determining the necessary correction is described in 12.5.
d) The geometrical conditions of the reference blocks and the test object shall be considered.
For further details, see Clause 8.
e) The geometry of the reference blocks, its dimensions, and the position of any reflectors, shall be
indicated on a case by case basis in the specific standards and specifications.
f) The position and number of reflectors shall relate to the scanning of the entire test volume.
g) The most commonly used reflectors are:
1) large planar reflectors, compared to the beam width, perpendicular to the beam axis (e.g. back wall);
2) flat-bottomed holes;
3) side-drilled holes;
4) grooves or notches of various cross-sections
h) When reference blocks are submerged, e.g. for immersion testing, the influence of water in the holes
shall be considered or the ends of the holes shall be plugged.
i) The consequences of temperature differences between test object, probes, and reference blocks shall be
considered and compared to the requirements for the accuracy of the test.
j) If necessary, the reference blocks shall be maintained within the specified temperature range during
the testing.
ISO 16811:2025(en)
6.6 Specific test blocks
In certain cases, specific blocks, e.g. with identified natural discontinuities, can be used to optimise the test
technique and to check the stability of the test sensitivity.
7 Categories of test objects
The requirements for range and sensitivity setting will depend on the geometrical form of the test object.
Five categories of test objects are specified in Table 2.
Table 2 — Categories of test objects
Category Feature Section in x-direction Section in y-direction
1 Plane parallel surfaces (e.g. plate/
sheet)
2 Parallel, uniaxially curved surfac-
es (e.g. tubes)
3 Parallel surfaces curved in more
than one direction (e.g. dished
ends)
4 Solid material of circular cross
section (e.g. rods and bars)
5 Complex shapes (e.g. nozzles,
sockets)
8 Test objects, reference blocks and reference reflectors
Requirements for geometrical features of test objects, reference blocks and reference reflectors in general
are contained in Table 3 and Table 4.

ISO 16811:2025(en)
Table 3 — Reference blocks — Requirements for scanning surface, wall thickness and reflectors
Requirements when using back-wall echoes
Straight-beam probe Angle-beam probe Condition
2λs
e>
D
eff
λs
ee, >
D
eff
Key
1 sound beam diameter
Requirements when using side-drilled holes
Straight-beam probe Angle-beam probe Condition
D ≥15, λ
SDH
2λs
e>
D
eff
λs
ee, >
D
eff
sN>15,
eff
Requirements when using disc-shaped reflectors
Straight-beam probe Angle-beam probe Condition
λs
D <
DSR
D
eff
λs
ee, >
D
eff
sN>07,
eff
Key
1 sound beam diameter
ISO 16811:2025(en)
TTabablele 3 3 ((ccoonnttiinnueuedd))
Requirements for test surface and wall thickness
Straight-beam probe Angle-beam probe Condition
d larger than the length of the dead
zone for α equal to 0°.
d > 5 λ for
α > 0°
e > 1,5 w
1 ps
e > 1,5 l
2 ps
e > 1,5 D
3 ps
Requirements when using spherical-shaped reflectors
Straight-beam probe Angle-beam probe Condition
s > 1,5 N with
eff
πλs
D <
SSH
D
eff
β ≤ 60°
λs
ee, >
D
eff
ISO 16811:2025(en)
Table 4 — Reference blocks and reference reflectors for category 1 objects
Reference blocks and reference
Wall thickness, d, in mm Conditions
reflectors
2λs
e>
D
eff
10 ≤ d ≤ 15
15 ≤ d ≤ 20
D ≥15, λ
SDH
20 ≤ d ≤ 40
d−10
e =
d−10
d > 40 e ≤
9 Probes
9.1 General
Contouring of the probe shoe, for categories 2 to 5 of Table 2, may be necessary to avoid probe rocking, i.e. to
ensure good, uniform, acoustic contact and a constant beam angle in the test object.
Contouring is only possible with probes having a hard-plastic delay block (normally dual-transducer
straight-beam probes or angle-beam probes with wedges).
The following conditions for the different categories exist (see Table 2 and Figure 1):
— Category 1: No probe contouring necessary in either x- or y-direction;
— Categories 2 and 4: Contouring in x-direction for all probes (angle-beam probe orientation in x-direction
shall be longitudinally curved; angle-beam probe orientation in y-direction shall be transversely curved);

ISO 16811:2025(en)
— Categories 3 and 5: Contouring in both x- or y-directions: Probe face longitudinally and transversely curved.
The use of contoured probes necessitates setting the range and sensitivity on reference blocks contoured
similar to the test object, or the application of mathematical correction factors.
When using Formula (1) or Formula (2), problems due to low energy transmission or beam misalignment
are avoided.
9.2 Longitudinally curved probes
9.2.1 Convex scanning surface
For scanning on convex surfaces, the probe face shall be contoured when the diameter of the test object, D ,
obj
is below ten times the length of the probe shoe, l , (see Figure 1):
ps
Dl<10 (1)
objps
9.2.2 Concave scanning surface
On a concave scanning surface, the probe face shall always be contoured, unless adequate coupling can be
achieved due to very large radii of curvature.
9.3 Transversely curved probes
9.3.1 Convex scanning surface
For scanning on convex surfaces, the probe face shall be contoured when the diameter of the test object, D ,
obj
is below ten times the width of the probe shoe, w , (see Figure 1):
ps
Dw<10 (2)
objps
Key
1 transversely curved
2 longitudinally curved
Figure 1 — Length, l , and width, w , of probe shoe in direction of curvature of the test object
ps ps
ISO 16811:2025(en)
9.3.2 Concave scanning surface
On a concave scanning surface, the probe face shall always be contoured, unless adequate coupling can be
achieved due to very large radii of curvature.
10 Determination of probe index point and beam angle
10.1 General
a) For straight-beam probes there is no requirement to determine probe index point and beam angle as it
is assumed that the probe index point is in the centre of the probe face and the angle of refraction is zero
degrees.
b) When using angle-beam probes, these parameters shall be determined in order that the position of a
reflector in the test object can be determined in relation to the probe position.
The techniques and reference blocks employed depend on the contouring of the probe face.
c) Measured beam angles depend on the sound velocity of the reference block used.
If the block is not made of non-alloy steel, its velocity shall be determined and recorded.
10.2 Flat angle-beam probes
10.2.1 Calibration block technique
Probe index point and beam angle shall be determined using calibration block No. 1 or calibration block No. 2
according to the specifications given in ISO 2400 or ISO 7963 respectively, depending on the size of the probe.
10.2.2 Reference block technique
An alternative technique using a reference block containing at least 3 side-drilled holes may be used. In this
case, a block as given in ISO 22232-3 shall be used.
10.3 Angle-beam probes curved longitudinally
10.3.1 Mechanical determination
a) Before contouring the probe face, the probe index point and beam angle shall be measured as described
in 10.2.1.
b) The incident angle at the probe face (α ) shall be calculated from the determined beam angle (α) and a
d
line, originating from the probe index point and parallel to the incident beam, shall be marked on the
side of the probe, as shown in Figure 2.
c) The incident angle is given by Formula (3):
 c 
d
αα=arcsin sin (3)
d  
c
 
t
where
c is the longitudinal wave velocity in the probe wedge (normally 2 730 m/s for acrylic glass);
d
c is the transverse wave velocity in the test object (3 255 m/s ± 15 m/s for non-alloy steel).
t
d) After contouring, the probe index point will have moved along the marked line, and its new position can
be measured by mechanical means directly on the probe housing, as shown in Figure 2.

ISO 16811:2025(en)
e) The beam angle shall be determined by maximizing the echo
...