prEN ISO 29601

Paints and varnishes - Corrosion protection by protective paint systems - Assessment of porosity in a dry film (ISO/DIS 29601:2025)

ISO 29601:2011 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 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 might have been penetrated by substances in contact with the coating during service.

Beschichtungsstoffe - Korrosionsschutz durch Beschichtungssysteme – Beurteilung der Porosität einer trockenen Beschichtung (ISO/DIS 29601:2025)

Diese Internationale Norm legt Verfahren zur Feststellung von Porosität in Beschichtungssystemen jeder
Schichtdicke für den Korrosionsschutz auf einem Stahlsubstrat oder anderen Substraten aus Metall fest. Die
in dieser Internationalen Norm angegebenen Vorgehensweisen basieren auf Verfahren, die zwei
verschiedene Prüfgerätetypen verwenden. Die Auswahl des Gerätes richtet sich nach der
Trockenschichtdicke. Diese Verfahren sind nur für die Prüfung elektrisch nichtleitender Schichten eines
Beschichtungssystems anwendbar.
Die festgelegten Prüfverfahren werden hauptsächlich für neue Beschichtungen angewendet, sie können
jedoch auch für Beschichtungen angewendet werden, die bereits in der Praxis gebraucht wurden. Im letzteren
Fall ist zu beachten, dass in das Beschichtungssystem Substanzen während der Lagerung eingedrungen sein
könnten.

Peintures et vernis - Anticorrosion par systèmes de peinture – Évaluation de la porosité d'un feuil sec (ISO/DIS 29601:2025)

L'ISO 29601:2011 spécifie des modes opératoires permettant de détecter l'existence de porosité dans un système de revêtement de peinture, quelle qu'en soit l'épaisseur, appliqué sur un subjectile en acier ou sur tout autre métal. Les modes opératoires fournis dans la présente Norme internationale sont basés sur des méthodes faisant appel à deux types d'équipement d'essai, le choix de l'équipement étant fonction de l'épaisseur du feuil sec. Ces modes opératoires ne s'appliquent qu'aux essais des couches électriquement non conductrices d'un système de peinture.
Les méthodes d'essai spécifiées sont destinées principalement aux revêtements neufs mais peuvent aussi être employées pour les revêtements déjà mis en service. Dans ce dernier cas, il est important de garder à l'esprit le fait que des substances en contact avec le revêtement ont pu y pénétrer pendant la période en service.

Barve in laki - Korozijska zaščita z zaščitnimi premaznimi sistemi - Ocenjevanje poroznosti suhega filma (ISO/DIS 29601:2025)

General Information

• Status: Not Published
• Publication Date: 14-Jul-2026
• ICS: 87.020 - Paint coating processes
• ICS: 87.040 - Paints and varnishes
• Technical Committee: CEN/TC 139 - Paints and varnishes
• Drafting Committee: CEN/TC 139 - Paints and varnishes
• Current Stage: 4599 - Dispatch of FV draft to CMC - Finalization for Vote
• Start Date: 12-Nov-2025
• Completion Date: 12-Nov-2025
• Ref Project: oSIST prEN ISO 29601:2025 - Paints and varnishes - Corrosion protection by protective paint systems - Assessment of porosity in a dry film (ISO/DIS 29601:2025)

Relations

• Revises: EN ISO 29601:2011 - Paints and varnishes - Corrosion protection by protective paint systems - Assessment of porosity in a dry film (ISO 29601:2011)
• Effective Date: 18-Jan-2023

Overview

prEN ISO 29601 / ISO/DIS 29601:2025 - "Paints and varnishes - Corrosion protection by protective paint systems - Assessment of porosity in a dry film" - specifies standardized procedures for detecting porosity (pinhole/holiday defects) in protective paint systems on steel and other metallic substrates. The standard covers test principles, required equipment, test voltages tied to dry film thickness, inspection procedures, result expression and reporting. It applies only to the electrically non‑conductive parts of paint systems and is intended mainly for new coatings (but can be used for in‑service coatings with caution).

Key topics and requirements

• Scope and definitions: porosity, discontinuity, nominal and mean dry film thickness (NDFT/mean DFT), inspection area and dielectric strength.
• Two test methods:
  • Low‑voltage pinhole detection (wet‑sponge technique) - uses moisture/wetting agent to complete an electrical path through discontinuities; typically battery‑operated, portable units.
  • High‑voltage holiday detection - uses DC or pulsed DC high voltage to induce electrical breakdown at defects; AC high‑voltage generators are not permitted.
• Equipment requirements: sensitivity, alarm systems, controlled output voltage, correct electrical path and use of conductive liquid for low‑voltage testing.
• Procedure essentials: selection of method based on dry film thickness, paint condition before testing, wetting agent selection, preparation and movement of probe, and verification of output voltage.
• Results and reporting: how to express inspection results, required test report content and reference to an annex (table of mean dry film thicknesses with recommended test voltages).

Practical applications

• Quality control and inspection of protective coatings on steel structures such as bridges, ships, offshore platforms, tanks and industrial equipment.
• Pre‑delivery checks in manufacturing, on‑site maintenance assessment, and acceptance testing during new construction or refurbishment.
• Helps prevent premature corrosion by detecting porosity that compromises dielectric strength and barrier protection.

Who should use this standard

• Coating inspectors and NDT technicians
• Corrosion engineers and specification writers
• Asset owners, contractors and fabricators in marine, oil & gas, infrastructure and heavy industry
• QA/QC teams responsible for protective paint systems

Related standards

• ISO 12944 series (corrosion protection by paint systems) - complementary guidance
• ISO 19840 (dry film thickness measurement)
• ISO 16276‑1 and ISO 16276‑2 (adhesion testing by pull‑off and cross‑cut/X‑cut)

Keywords: porosity assessment, dry film porosity, holiday detection, pinhole detector, protective paint systems, corrosion protection, ISO 29601, paints and varnishes, dry film thickness.

Standards Content (Sample)

SLOVENSKI STANDARD
01-maj-2025
Barve in laki - Korozijska zaščita z zaščitnimi premaznimi sistemi - Ocenjevanje
poroznosti suhega filma (ISO/DIS 29601:2025)
Paints and varnishes - Corrosion protection by protective paint systems - Assessment of
porosity in a dry film (ISO/DIS 29601:2025)
Beschichtungsstoffe - Korrosionsschutz durch Beschichtungssysteme – Beurteilung der
Porosität einer trockenen Beschichtung (ISO/DIS 29601:2025)
Peintures et vernis - Anticorrosion par systèmes de peinture – Évaluation de la porosité
d'un feuil sec (ISO/DIS 29601:2025)
Ta slovenski standard je istoveten z: prEN ISO 29601
ICS:
25.220.20 Površinska obdelava Surface treatment
87.040 Barve in laki Paints and varnishes
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
International
Standard
ISO/DIS 29601
ISO/TC 35/SC 14
Paints and varnishes — Corrosion
Secretariat: DIN
protection by protective paint
Voting begins on:
systems — Assessment of porosity
2025-03-13
in a dry film
Voting terminates on:
2025-06-05
Peintures et vernis — Anticorrosion par systèmes de peinture —
Évaluation de la porosité d'un feuil sec
ICS: 87.020
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
ISO/CEN PARALLEL PROCESSING
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS.
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION.
Reference number
ISO/DIS 29601:2025(en)
DRAFT
ISO/DIS 29601:2025(en)
International
Standard
ISO/DIS 29601
ISO/TC 35/SC 14
Paints and varnishes — Corrosion
Secretariat: DIN
protection by protective paint
Voting begins on:
systems — Assessment of porosity
in a dry film
Voting terminates on:
Peintures et vernis — Anticorrosion par systèmes de peinture —
Évaluation de la porosité d'un feuil sec
ICS: 87.020
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2025
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
STANDARDS MAY ON OCCASION HAVE TO
ISO/CEN PARALLEL PROCESSING
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
BE CONSIDERED IN THE LIGHT OF THEIR
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
or ISO’s member body in the country of the requester.
NATIONAL REGULATIONS.
ISO copyright office
RECIPIENTS OF THIS DRAFT ARE INVITED
CP 401 • Ch. de Blandonnet 8
TO SUBMIT, WITH THEIR COMMENTS,
CH-1214 Vernier, Geneva
NOTIFICATION OF ANY RELEVANT PATENT
Phone: [phone]
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION.
Email: [e-mail]
Website: www.iso.org
Published in Switzerland Reference number
ISO/DIS 29601:2025(en)
ii
ISO/DIS 29601:2025(en)
Contents Page
Foreword .iv
Introduction .v
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
5.1.1 General .2
5.1.2 Electric path .2
5.1.3 Sensitivity and alarm .2
5.1.4 Conductive liquid .2
5.2 High-voltage holiday detectors .3
5.2.1 General .3
5.2.2 Electrical source .3
5.2.3 Equipment shall be operated either by DC or pulsed DC. High-voltage AC
generators shall not be used for testing. .3
5.2.4 Electrical path .3
5.2.5 Alarm .3
5.2.6 Controlled output voltage.3
6 Procedure . 3
6.1 Selection of test method .3
6.2 Low-voltage pinhole detection .4
6.2.1 Test voltage.4
6.2.2 Paint conditions before testing .4
6.2.3 Wetting agent .4
6.2.4 Preparation before testing .4
6.2.5 Testing .4
6.3 High-voltage holiday detection .4
6.3.1 Paint conditions before testing .4
6.3.2 Test voltage settings and calculation .5
6.3.3 output voltage verification .5
6.3.4 preparation before testing .5
6.3.5 Testing .5
7 Expression of results . 5
8 Test report . 6
Annex A  Table of mean dry film thicknesses and their corresponding recommended test
voltages . 7
Bibliography . 9

iii
ISO/DIS 29601:2025(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 documents 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/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 [or Project Committee] ISO/TC 35, paints and varnishes,
Subcommittee SC 14, Protective paint systems for steel structures.
This third edition cancels and replaces the second edition (ISO 29601:2012), which has been technically
revised.
The main changes are as follows:
— editorial update
A list of all parts in the ISO ##### series can be found on the ISO website.
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
ISO/DIS 29601:2025(en)
Introduction
This International Standard supplements the ISO 12944 series (see the Bibliography) with regard to the
detection of porosity in a dry film. If specified or agreed, the standard can also be used for other applications.
The objective of this International Standard 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 International Standard complements ISO 19840, which concerns the measurement of the thickness
of dry films on rough surfaces, and ISO 16276 1 and ISO 16276 2, which concern the measurement of the
adhesion of a coating by pull-off testing (Part 1) and by cross-cut and X cut testing (Part 2).

v
DRAFT International Standard ISO/DIS 29601:2025(en)
Paints and varnishes — Corrosion protection by protective
paint systems — Assessment of porosity in a dry film
1 Scope
This International Standard 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 International
Standard 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
might have been penetrated by substances in contact with the coating during service.
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 19840, Paints and varnishes — Corrosion protection of steel structures by protective paint systems —
Measurement of, and acceptance criteria for, the thickness of dry films on rough surfaces
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
porosity
presence of one or more discontinuities in a coating
3.2
discontinuity
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
[SOURCE: ISO 19840:2004]
3.4
mean dry film thickness
arithmetic mean of all the individual dry film thicknesses in the inspection area
[SOURCE: ISO 19840:2004]
...