ISO/FDIS 29601

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ISO/DISFDIS 29601
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ISO/TC 35/SC 14
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Secretariat: DIN
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Date: 2025-05-202026-01-15
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Paints and varnishes — Corrosion protection by protective paint
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systems — Assessment of porosity in a dry film
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Peintures et vernis — Anticorrosion par systèmes de peinture — Évaluation de la porosité d'un feuil sec
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FDIS stage
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Warning for WD’s and CD’s
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This document is not an ISO International Standard. It is distributed for review and comment. It is subject to change
without notice and may not be referred to as an International Standard.
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they are aware and to provide supporting documentation.
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TThhiiss d drraftaft i iss s suubbmmiitttteded t too a pa pararallel vallel vootte e iinn I ISSOO,, C CEENN.
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ISO/DISFDIS 29601:20252026(en)
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ISO/DISFDIS 29601:20252026(en)
Contents
Foreword . iv
Introduction . iv
1 Scope . iv
2 Normative references . iv
3 Terms and definitions . iv
4 Principle. iv
5 Test equipment . iv
5.1 Low-voltage pinhole detectors . iv
5.2 High-voltage holiday detectors . iv
6 Procedure . iv
6.1 Selection of test method . iv
6.2 Low-voltage pinhole detection . iv
6.3 High-voltage holiday detection . iv
7 Expression of results . iv
8 Test report . iv
Table of mean dry film thicknesses and their corresponding recommended test voltages . iv
Bibliography . iv
Foreword . v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Test equipment . 2
5.1 Low-voltage pinhole detectors. 2
5.2 High-voltage holiday detectors . 3
6 Procedure . 4
6.1 Selection of test method . 4
6.2 Low-voltage pinhole detection . 4
6.3 High-voltage holiday detection . 5
7 Expression of results . 6
8 Test report . 6
Annex A (normative) Mean dry-film thicknesses and corresponding test voltages . 8
Bibliography . 10

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ISO/DISFDIS 29601:20252026(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
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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).
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ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
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This document was prepared by Technical Committee ISO/TC 35, Paints and varnishes, Subcommittee SC 14,
Protective paint systems for steel structures, in collaboration with the European Committee for Standardization
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(CEN) Technical Committee CEN/TC 139, Paints and varnishes, in accordance with the Agreement on technical
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cooperation between ISO and CEN (Vienna Agreement).
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This second edition cancels and replaces the first edition (ISO 29601:2011), which has been technically
revised.
The main changes are as follows:
— — general (editorial) update of terminology ;
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— — update on cleaning procedure before measurement;
— — update on verification of test equipment ;
— — update on voltage calculation;
— — low voltage measurement was confirmed.
Any feedback or questions on this document should be directed to the user’s national standards body. A
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complete listing of these bodies can be found at www.iso.org/members.htmlwww.iso.org/members.html.
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ISO/DISFDIS 29601:20252026(en)
Introduction
This document supplements the ISO 12944 series with regard to the detection of porosity in a dry film. If
specified or agreed, this document can also be used for other applications.
The objective of this document is to achieve uniformity of practice for the detection of porosity in a dry film.
The methods chosen entail the detection of porosity using one of two types of equipment, a low-voltage
pinhole detector or a high-voltage holiday detector.
This document complements the following International Standards:
— ISO 19840, which concerns the measurement of the thickness of dry films on rough surfaces; Formatted: List Continue 1, No bullets or numbering
 ISO 16276-1
— , which concerns the measurement of the adhesion of a coating by pull-off testing ; Formatted: List Continue 1, No bullets or numbering
— ISO 16276-2, which concerns the measurement of the adhesion by cross-cut and X -cut testing.
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ISO/DISFDIS 29601:20252026(en)
Paints and varnishes — Corrosion protection by protective paint
systems — Assessment of porosity in a dry film
1 Scope
This document specifies procedures for detecting the presence of porosity in a protective paint system of any
thickness on a steel or other metallic substrate. The procedures given in this document are based on methods
using two different types of test equipment, the choice of equipment depending on the dry-film thickness.
These procedures are only applicable to the testing of electrically non-conductive parts of a paint system.
The test methods specified are mainly intended for use with new coatings, but can also be used for coatings
which have been in service for some time. In the latter case, it is important to bear in mind that the coating
can have been penetrated by substances in contact with the coating during service.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
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— — ISO Online browsing platform: available at https://www.iso.org/obphttps://www.iso.org/obp
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— — IEC Electropedia: available at https://www.electropedia.org/https://www.electropedia.org/
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3.1
porosity
presence of one or more discontinuities in a coating
3.2
discontinuity
holiday
hole, pit, pinhole, void, crack, thin spot, inclusion, contamination or other flaw in a coating that significantly
lowers the dielectric strength of the coating
Note 1 to entry: Certain types of discontinuity can also be described as a holiday.
3.3
nominal dry-film thickness
NDFT
dry-film thickness specified for each coat or for the whole paint system to achieve the required durability
[SOURCE: ISO 19840:2012, 3.6]
3.4
mean dry-film thickness
arithmetic mean of all the individual dry-film thicknesses in the inspection area
[SOURCE: ISO 19840:2012, 3.5]
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ISO/DISFDIS 29601:20252026(en)
3.5
inspection area
designated area for inspection as defined in the specification
Note 1 to entry: If inspection areas are not defined, the whole structure is a single inspection area.
3.6
electrical breakdown
process that occurs when an insulating material, subjected to high enough voltage, suddenly becomes an
electrical conductor and electrical current flows through it
3.7
dielectric strength
maximum voltage required to produce a dielectric breakdown through a material
4 Principle
Porosity in a protective paint system applied to a conductive metal surface is detected either by low-voltage
wet-sponge testing or high-voltage holiday testing. Low-voltage pinhole detectors use moisture to conduct
electrical current through any discontinuity in the coating. High-voltage holiday detectors generate electrical
breakdown in a discontinuity when the discontinuity has a lower dielectric strength than the paint system.
In both cases, the apparatus is electrically connected to the metallic substrate, often by means of a signal return
cable, and a DC voltage is applied by means of a probe. When a discontinuity is detected, an alarm is triggered.
The test voltage is determined by the thickness of the non-conductive part of the coating.
5 Test equipment
5.1 Low-voltage pinhole detectors
5.1.1 General
Low-voltage pinhole detectors are normally battery-operated for portability. They can either be single-
voltage, 9 V or 90 V, or dual-voltage, switchable between 9 V and 90 V.
Verify correct working and functionality ofthat the apparatus is working and functioning correctly, e.g. if the
output voltage, or the resistance if it meetsmeet the manufacturer's recommendation. If possible, the
functionality can be tested with a known discontinuityholiday on the item or, if agreed, an a artificialartificially
made holidaydiscontinuity.
5.1.2 Electric path
To provide an electrically conductive path through any discontinuity in the coating, an open-cell sponge
moistened with tap water is used to apply the voltage. A cable with a suitable spring-operated connector
(crocodile clip) is required to make contact to the bare substrate to form the si
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