ISO 24489:2024

Non-destructive testing - Acoustic emission testing - Detection of corrosion at atmospheric and low-pressure metallic storage tank floors

This document describes the testing methodology based on acoustic emission (AE) for atmospheric and low-pressure (less than or equal to 50 kPa on top of the tank) metallic storage tank floors and the classification system to be used for test results. This document applies to acoustic emission testing (AT) for corrosion severity of atmospheric metal storage tank floors. The technique is limited to tank floors made of construction steel and relies on an active corrosion process. It applies only in cases where corrosion of the floor is the governing damage mechanism. Good results will be obtained providing corrosion conditions have not changed.

Titre manque

General Information

• Status: Published
• Publication Date: 11-Jan-2024
• ICS: 19.100 - Non-destructive testing
• Technical Committee: ISO/TC 135/SC 9 - Acoustic emission testing
• Drafting Committee: ISO/TC 135/SC 9/WG 10 - Acoustic emission testing of atmospheric pressure storage tank
• Current Stage: 6060 - International Standard published
• Start Date: 12-Jan-2024
• Due Date: 22-Jul-2023
• Completion Date: 12-Jan-2024

Overview

ISO 24489:2024 - Non-destructive testing (NDT) - Acoustic emission testing (AE) - provides a standardized methodology to detect and classify corrosion on atmospheric and low‑pressure (≤ 50 kPa) metallic storage tank floors. The standard applies to floors made of construction steel and is based on detecting acoustic emission generated by an active corrosion process. It specifies test equipment, personnel qualification, test procedures, data interpretation and a classification system with maintenance recommendations.

Key topics and technical requirements

• Scope: Atmospheric and low‑pressure metallic tank floors where corrosion is the primary damage mechanism; good results expected if corrosion conditions are stable.
• Personnel: Test personnel should be competent - ISO 9712 or equivalent recommended.
• AE system components: AE instrument and software, sensors, preamplifiers, cables, couplant and mounting devices. All essential parts must be documented in a written test instruction.
• Sensor requirements:
  • Main response frequency 20 kHz–80 kHz
  • Minimum sensitivity ≥ 60 dB (referred to 1 V·s/m) in appropriate wave settings
  • Shielding against radio‑frequency/electromagnetic noise; metallic housing electrically isolated from tank
  • Stability within ±3 dB across expected frequency and temperature range
  • Verification: a Hsu‑Nielsen source at 100 mm must produce a peak amplitude ≥ 80 dB AE
• Preamplifiers and cables:
  • Preamplifier circuit noise RMS < 7 µV
  • Cables shielded; sensor‑to‑preamplifier cable length ≤ 1 m unless losses are accounted for
• Test procedures:
  • Site inspection, sensor mounting, instrument setup, simulation of AE sources, determination of sound velocity, background noise checks, sensitivity/threshold adjustment
  • Consideration of tank liquid level and interfering AE sources
• Data handling & classification:
  • Data acquisition, processing and a classification system (including time‑difference location analysis - Annex A, and overall floor condition analysis - Annex B)
• Documentation: Written test instructions, records and comprehensive test reports.

Applications and users

ISO 24489:2024 is intended for:

• NDT service providers and AE technicians
• Storage tank operators, asset managers and maintenance planners in petrochemical, oil & gas, terminals and utilities
• Inspection engineers and regulatory bodies evaluating floor corrosion risk

Practical benefits include early detection of active corrosion, prioritization of maintenance, reduced unplanned outages and support for risk‑based inspection programs.

Related standards

• ISO 12716 - Acoustic emission vocabulary
• EN 13477‑2 - AE equipment characterization (verification)
• ISO 9712 - Personnel qualification (recommended)

Keywords: ISO 24489:2024, acoustic emission testing, AE, non‑destructive testing, corrosion detection, metal storage tank floors, atmospheric tank, low‑pressure.

Standards Content (Sample)

International
Standard
ISO 24489
First edition
Non-destructive testing — Acoustic
2024-01
emission testing — Detection of
corrosion at atmospheric and low-
pressure metallic storage tank
floors
Reference number
© ISO 2024
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: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 General principles . 2
5 Qualification of test personnel . 2
6 Test equipment . 2
6.1 Acoustic emission testing system.2
6.2 Acoustic emission sensors .3
6.3 Acoustic emission signal cables .3
6.4 Couplant .3
6.5 Preamplifiers .3
6.6 Power signal cables .3
6.7 Filters .4
6.8 Acoustic emission instrument .4
6.9 Maintenance and verification of test equipment .5
7 Actions before testing . 5
7.1 General information.5
7.2 Documents.5
7.3 Site inspection .5
7.4 Preparation of test instruction and record sheet .5
7.5 Sensor mounting .5
7.6 Setting of the acoustic emission instrument .6
7.6.1 First steps .6
7.6.2 Simulation of acoustic emission sources.6
7.6.3 Determination of sound velocity .6
7.6.4 Background noise .7
7.6.5 Sensitivity check and threshold .7
8 Performing the test . 8
8.1 Storage tank liquid level and condition .8
8.2 Interfering acoustic emission sources .9
8.3 Data acquisition and observations during acoustic emission testing .9
9 Interpretation of test results . 9
9.1 General requirements .9
9.2 Data processing.9
9.3 Classification system for the corrosion status and recommendations for maintenance .10
10 Documentation . 10
10.1 General .10
10.2 Written test instruction .10
10.3 Test records .11
10.4 Test report .11
Annex A (informative) Classification method based on time-difference location analysis and an
example .13
Annex B (informative) Classification method based on overall floor condition analysis and an
example .18
Bibliography .23

iii
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 9, Acoustic emission testing.
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.

iv
Introduction
Industrial applications of acoustic emission testing for atmospheric metal storage tanks have been gaining
wider usage alongside marked improvement of acoustic emission testing technologies. The effectiveness of
any application of acoustic emission testing depends upon proper and correct use of the acoustic emission
instruments and test techniques.
In addition, existing international acoustic emission standards lack a specification of a classification system
with the associated recommendations for maintenance.
The purpose of this document is to provide requirements for the testing equipment, testing procedures and
classification system for acoustic emission testing for corrosion of atmospheric metal storage tank floors.

v
International Standard ISO 24489:2024(en)
Non-destructive testing — Acoustic emission testing —
Detection of corrosion at atmospheric and low-pressure
metallic storage tank floors
1 Scope
This document describes the testing methodology based on acoustic emission (AE) for atmospheric and low-
pressure (less than or equal to 50 kPa on top of the tank) metallic storage tank floors and the classification
system to be used for test results.
This document applies to acoustic emission testing (AT) for corrosion severity of atmospheric metal storage
tank floors.
The technique is limited to tank floors made of construction steel and relies on an active corrosion process.
It applies only in cases where corrosion of the floor is the governing damage mechanism. Good results will
be obtained providing corrosion conditions have not changed.
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.
ISO 12716, Non-destructive testing — Acoustic emission inspection — Vocabulary
EN 13477-2, Non-destructive testing — Acoustic emission testing — Equipment characterisation — Part 2:
Verification of operating characteristic
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 12716 and the following 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/
3.1
acoustic emission testing
AT
testing of a test object during controlled stimulation using acoustic emission instrumentation to detect and
analyse sources of acoustic emission
[SOURCE: EN 1330-9:2017, 2.5.1]
3.2
Hsu-Nielsen source
device to simulate an acoustic emission event using the fracture of a brittle graphite lead in a suitable fitting
Note 1 to entry: Hue-Nielsen source is according to Figure 1.

Key
1 pencil
2 guide ring
3 graphite lead
hardness grade 2 H
diameter 0,5 mm
length 3,0 ± 0,5 mm
Figure 1 — Hsu-Nielsen source
4 General principles
During the operation of atmospheric metallic storage tanks, the tank floor is potentially subjected to a
corrosive environment and due to the ongoing corrosion process AE waves are generated.
Elastic waves are generated by AE events from the corrosion process itself or peeling and cracking of
corrosion products on the tank floor and are transmitted to the surface of the tank wall predominantly
through the storage medium.
The purpose of AT of storage tank floors is to detect the AE signals related to the corrosion process with AE
sensors mounted in the lower part of the tank wall.
By receiving and analysing these signals, the severity of the tank floor corrosion condition can be determined
and assessed.
5 Qualification of test personnel
AT shall be performed by competent personnel. In order to ensure that this is the case, it is recommended
that the personnel meet the requirements of ISO 9712 or equivalent.
6 Test equipment
6.1 Acoustic emission testing system
An AT system consists of an AE instrument including software, AE sensors, preamplifiers, interconnecting
cables and mounting devices holding the sensors.
All essential parts of the AT system shall be specified in a written test instruction agreed at the time of
enquiry or order (see 10.2).
6.2 Acoustic emission sensors
The requirements for AE sensors are as follows:
a) The main response frequency of the sensors shall be between 20 kHz and 80 kHz.
b) The minimum sensitivity shall be equivalent to or greater than 60 dB referred to 1 Vs/m in surface wave
sound field setting or in longitudinal wave setting.
c) Sensors shall be shielded against radio frequency and electromagnetic noise interference by proper
shielding practice or by differential element design, or both.
d) The metallic housing of each AE sensor shall be electrically isolated from the metallic test object.
e) The AE sensors shall be stable over the response frequency and temperature range of use and shall not
exhibit sensitivity changes greater than 3 dB over this range.
f) To get sufficient sensitivity, a Hsu-Nielsen source at a distance of 100 mm from the sensor shall generate
a peak amplitude of at least 80 dB .
AE
g) The verification of the sensors shall be performed according to sensor-specific manuals provided by the
manufacturer.
6.3 Acoustic emission signal cables
The requirements for AE signal cables used to connect AE sensors and preamplifiers are as follows:
a) Signal cables connecting sensors and preamplifiers shall be shielded against electromagnetic
interference.
b) Cable length shall not exceed 1 m, unless the length-depending signal loss is considered and acceptable.
This requirement may be omitted where the preamplifier is integrated in the shielded sensor housing.
6.4 Couplant
The used couplant shall provide an effective coupling quality so that the sensor tracks the motion of the
surface.
6.5 Preamplifiers
The preamplifiers may be separate or may be mounted in the sensor housing.
The requirements for preamplifiers are as follows:
a) The RMS voltage of preamplifiers circuit noise shall be less than 7 μV.
b) The preamplifiers shall be stable over the response frequency and temperature range of use and shall
not exhibit sensitivity changes greater than 3 dB over this range.
c) The preamplifiers response frequency shall match that of the sensors, and the gain of the preamplifiers,
usually 34 dB, 40 dB or 46 dB, shall not cause saturation of the measurement chain.
d) If the preamplifiers are of differential design, a minimum of 40 dB of common-mode rejection shall be
provided.
6.6 Power signal cables
The requirements for power-signal cables providing power to the preamplifier and conducting the amplified
signal to the main processor are as follows:
a) The cables shall be shielded against electromagnetic noise.

b) Signal loss shall be no more than 1 dB per 30 m of cable length. 150 m is the recommended maximum
cable length to avoid excessive signal attenuation.
c) The signal loss of cables depends on type of cable, frequency and length. With cable length above 30 m,
the resulting attenuation and the voltage drop-off of the DC supply shall be evaluated and considered in
the data analysis.
6.7 Filters
The response frequency of filters in the preamplifiers and the AE instrument shall match that of the AE
sensors.
6.8 Acoustic emission instrument
The requirements for the AE instrument are as follows:
a) The AE instrument shall have enough AE channels to cover the area to be tested.
b) For each channel, the AE instrument shall display and record arrival time, threshold, peak amplitude,
ring-down count, energy, rise time and duration for each hit as a minimum.
c) The individual sampling frequency of each channel for acquisition of waveforms shall not be less than
10 times the sensors’ centre response frequency.
d) The measurement inaccuracy for a threshold above 40 dB shall not exceed ± 1 dB.
AE
e) The measurement inaccuracy for ring-down counts shall not exceed ± 5 %.
f) The measurement inaccuracy for peak amplitudes above 40 dB shall not exceed ± 1 dB.
AE
g) The measurement inaccuracy for energy above 40 dB shall not exceed ± 5 %.
AE
h) The measurement inaccuracy for the external parametric inputs, such as pressure, liquid level and
temperature, shall not exceed 2 % of the full range.
i) The resolution of rise time, duration and arrival time for each channel shall be less than or equal to 1 μs.
j) The error of arrival time measurement between all channels shall be not more than 2 µs.
k) The electronic noise levels shall be equal to or less than 20 dB in the frequency range from 20 kHz to
AE
80 kHz.
l) The usable dynamic range shall be at least 65 dB.
m) The AE instrument shall be capable of processing, storing and displaying at least 20 hits per second at
all channels.
n) The delay and display from the arrival of the AE hits shall not exceed 10 seconds.
o) The real-time update time for diagrams shall not be more than 5 s.
p) An alarm shall occur if the hit rate exceeds the capability of the AE instrument.
q) A warning shall occur when the storage space runs low.
r) During data acquisition, AE software shall be capable of displaying the following diagrams:
1) any AE parameter versus time;
2) one AE parameter versus another AE parameter;
3) tank floor circular planar locations.
s) The AE analysis software shall provide functions to replay and analyse the recorded AT data.

6.9 Maintenance and verification of test equipment
The performance of the AT system shall be verified at specified intervals in accordance with
EN 13477-2.
7 Actions before testing
7.1 General information
Prior to the specification of the test, the following information shall be provided:
a) the purpose of the test;
b) details of the storage tank to be tested;
c) the requirements for surface preparation;
d) the acceptance criteria, if specified;
e) the requirements in relation to the test report;
f) details of the qualification of test personnel.
7.2 Documents
Before performing an AE test, the following documents shall be provided for the storage tank to be tested,
as a minimum:
a) design and fabricating documents of the storage tank, e.g. product certification, quality certification
document, as-built drawing;
b) operation recording documents of the storage tank, e.g. type of liquid, the normal product and number
of years with this product, the highest level of liquid, range of operating temperature and abnormal
conditions;
c) previous test reports;
d) other documents, e.g. drawings and records showing repairs or modifications.
7.3 Site inspection
Prior to testing, a site inspection shall be carried out to find all interference factors, such as mechanical
impact, electromagnetic interference and vibration.
The interference of these factors shall be eliminated or sufficiently reduced during on-site AT.
7.4 Preparation of test instruction and record sheet
The test instruction (see 10.2) and record sheets (see 10.3) shall be prepared in accordance with the NDT
procedure, storage tank and site conditions.
The instrument, applicable sensors and surface conditions of the storage tank shall be specified.
7.5 Sensor mounting
The first row of sensors is placed on the tank wall near to the tank floor, and it shall be ensured that they are
above the height of the sediment in the tank. Thick layers of sediment affect the sensitivity of AT.
A second row of sensors (guard sensors) shall be mounted when noise from higher up in the tank (e.g.
condensation) can be expected.

The second row of sensors shall be below the liquid level, usually at about 3 m height above the first row.
The sensors of each row shall be mounted at the same height.
Care shall be taken that the sensitivity of the sensors is similar.
The maximum spacing of adjacent sensors shall not exceed 15 m.
If there are manholes, nozzles and welded structures between two adjacent sensors, the maximum spacing
shall not exceed 13 m.
It is recommended that six to eight sensors are installed per row for a tank with a diameter of less than 25 m.
All the sensors shall be numbered and indicated in the schematic diagram of the tank.
The mounting of sensors shall meet the following requirements:
a) The sensors shall be installed according to the specified sensor array.
b) The place for the mounting of a sensor on the tank shall be smooth and showing the metallic lustre. The
coating can be kept when it is smooth and compacted and measured attenuation is acceptable.
b) Efficient couplants, such as vacuum grease or vaseline, are recommended.
d) Firm fixing of the sensors onto the tank shall be performed by a magnetic holding device, adhesive tape
or other devices and mounting materials that provide equivalent sensor adhesion over the test duration.
e) For tanks with interlayer or insulation, removal of insulation or interlayer material at sensor position to
allow sensor mounting directly onto the tank surface is the preferred solution.
f) AE waveguides (rods) may be used when feasible for the intended purpose of the test.
7.6 Setting of the acoustic emission instrument
7.6.1 First steps
Connect the sensors and preamplifiers with the corresponding channel input of the AT system by
...