ISO 7989-2:2021

Steel wire and wire products - Non-ferrous metallic coatings on steel wire - Part 2: Zinc or zinc-alloy coating

This document specifies the requirements for the coating mass per unit area, for other properties and also for testing of zinc or zinc-alloy coatings on steel wire and steel wire products of circular or other section.

Fils et produits tréfilés en acier — Revêtements métalliques non ferreux sur fils d'acier — Partie 2: Revêtements de zinc ou d'alliages de zinc

General Information

• Status: Published
• Publication Date: 25-Feb-2021
• ICS: 25.220.40 - Metallic coatings
• ICS: 77.140.65 - Steel wire, wire ropes and link chains
• Technical Committee: ISO/TC 17/SC 17 - Steel wire rod and wire products
• Drafting Committee: ISO/TC 17/SC 17/WG 15 - Non-ferrous metallic coatings on steel wire
• Current Stage: 6060 - International Standard published
• Start Date: 26-Feb-2021
• Due Date: 19-Oct-2021
• Completion Date: 26-Feb-2021

Relations

• Revises: ISO 7989-2:2007 - Steel wire and wire products - Non-ferrous metallic coatings on steel wire - Part 2: Zinc or zinc-alloy coating
• Effective Date: 11-Nov-2017

Overview

ISO 7989-2:2021 - "Steel wire and wire products - Non‑ferrous metallic coatings on steel wire - Part 2: Zinc or zinc‑alloy coating" specifies requirements and test methods for zinc and zinc‑alloy coatings applied to steel wire and wire products (circular or other sections). The standard covers coating mass per unit area, coating appearance and adherence, salt‑spray performance, dipping (immersion) testing and procedures for determining coating mass (gravimetric and gaseous volumetric methods).

Key topics and technical requirements

• Scope: Requirements for coating mass per unit area, other coating properties and test methods for zinc or zinc‑alloy coatings on steel wire.
• Coating material purity: Zinc ingots for hot‑dip coatings - minimum 99.9 % Zn (unless otherwise specified); electrolytic coatings - minimum 99 % Zn.
• Coating mass classes: Defined classes (A, AB, B, C, D and E) with minimum coating mass expressed in grams per square metre (g/m2). Class E introduced for certain zinc‑aluminium coatings.
• Salt‑spray resistance: Rated by multiplying the minimum coating mass by a normalized coefficient (h/g/m2). Coefficients: Zinc = 2 h/g/m2; Zn95Al5 (standard Zn‑Al) = 6 h/g/m2; advanced Zn‑Al coatings = 12 h/g/m2. Test acceptance: no more than 5 % dark brown rust after the calculated hours (ISO 9227).
• Coating appearance: Coating should be smooth and evenly distributed without bare patches or dross contamination; Zn‑Al coatings may darken over time without loss of performance.
• Dipping (immersion) test: Optional, specified by agreement. Table of minimum numbers and durations of dips for Classes A and AB (zinc‑alu dip durations differ).
• Adherence: Assessed by wrapping test per ISO 7802 / ISO 7989‑1:2006; adherence rated visually against a reference chart (values 1 to 5).
• Mass measurement methods: Gravimetric method (reference, higher accuracy) and gaseous volumetric method (faster, preferred for routine testing). Sampling rules and precautions included.

Practical applications and who uses it

ISO 7989-2:2021 is essential for:

• Manufacturers of galvanized and zinc‑alloy coated steel wire for specifying and controlling coating quality.
• Purchasers and engineers to define coating class, salt‑spray performance and special finishes in procurement.
• Quality laboratories and test houses conducting coating mass, salt‑spray, dipping and adherence tests.
• Standards writers and product specifiers coordinating coating requirements in product standards.

Use this standard to ensure consistent corrosion protection, verify coating conformity, and agree coating classes and test regimes between suppliers and customers.

Related standards

• ISO 7989-1:2006 (General principles)
• ISO 7802 (Wrapping test)
• ISO 9227 (Salt spray corrosion tests)
• ASTM B997 / ASTM B750 (reference for Zn‑Al alloy coatings)

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 7989-2
Second edition
2021-02
Steel wire and wire products — Non-
ferrous metallic coatings on steel
wire —
Part 2:
Zinc or zinc-alloy coating
Fils et produits tréfilés en acier — Revêtements métalliques non
ferreux sur fils d'acier —
Partie 2: Revêtements de zinc ou d'alliages de zinc
Reference number
©
ISO 2021
© ISO 2021
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 © ISO 2021 – All rights reserved

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Coating requirements. 2
4.1 Requirements for the coating material . 2
4.2 Requirements relating to coating on the wire . 2
4.2.1 Coating mass per unit area. 2
4.2.2 Coating requirements to salt-spray test . 3
4.2.3 Appearance of coating . 4
4.2.4 Dipping test . 4
4.2.5 Special finishes . 5
4.2.6 Adherence of coating . . 5
5 Test conditions . 6
5.1 Selection of samples . 6
5.2 Determination of coating mass per unit area . 7
5.2.1 General. 7
5.2.2 Gravimetric method . 7
5.2.3 Gaseous volumetric method . 8
5.3 Dipping test .13
5.3.1 Principle .13
5.3.2 Reagents .13
5.3.3 Preparation of test piece .13
5.3.4 Test procedure .13
5.3.5 Interpretation of results .14
Bibliography .15
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).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
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 17, Steel, Subcommittee SC 17, Steel wire
rod and wire products.
This second edition cancels and replaces the first edition (ISO 7989-2:2007), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— reference is also made to ASTM B997 for Zn-Al alloy coatings (see 4.1);
— coating mass Class E is introduced for zinc-aluminium coatings (see Table 1);
— coating requirements to salt-spray test is added, see 4.2.2;
— dipping test better specified for Zinc-Alu alloy coatings (see Table 3);
— correction of formulae in 5.2.3.6.
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 2021 – All rights reserved

INTERNATIONAL STANDARD ISO 7989-2:2021(E)
Steel wire and wire products — Non-ferrous metallic
coatings on steel wire —
Part 2:
Zinc or zinc-alloy coating
1 Scope
This document specifies the requirements for the coating mass per unit area, for other properties and
also for testing of zinc or zinc-alloy coatings on steel wire and steel wire products of circular or other
section.
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 7802, Metallic materials — Wire — Wrapping test
ISO 7989-1:2006, Steel wire and wire products — Non-ferrous metallic coatings on steel wire — Part 1:
General principles
ISO 9227, Corrosion tests in artificial atmospheres — Salt spray tests
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
wire with zinc or zinc-alloy coating
wire where the coating has first been applied to protect it against corrosion
Note 1 to entry: Steel wire and steel wire products of circular or other sections are produced in a continuously
hot dip coated/galvanized or continuously electro galvanized process. The coating method may be hot dipping
in a bath of molten zinc, or by means of an aqueous solution of suitable electrolyte. In the hot dipping process,
wiping media may be used to modify the coating mass per unit area.
3.2
zinc or zinc alloy coating
coating composed of zinc or zinc alloy, where the zinc alloy is zinc to which other elements have been
deliberately added in order to obtain particular characteristics, and in which the quantity of zinc is at
least 50 %
Note 1 to entry: The most common alloy elements are aluminium, tin and nickel, but other elements may also be
considered.
3.3
coating mass per unit area
mass of zinc or zinc alloy per unit of surface area of bare wire.
Note 1 to entry: This is expressed in grams per square metre of surface.
3.4
zinc-alu alloy coating
Zn95Al5 or an advanced metallic coating
3.5
advanced metallic coating
metallic coating which reaches specific requirements
Note 1 to entry: Examples of advanced metallic coatings are Zn90 % + 10 % aluminium and Zn95 % + 5 %
aluminium with 0,2 % to 0,5 % magnesium.
4 Coating requirements
4.1 Requirements for the coating material
The zinc or zinc alloy used for the coating shall be specified at the time of the enquiry and order. For
zinc alloys not mentioned in this document, the alloy shall be specified at the enquiry and order.
NOTE For Zn-AI alloy coatings, reference is made to ASTM B997 or ASTM B750.
The ingot of the material used for the zinc coating shall be of minimum 99,9 % purity unless otherwise
stated in the relevant product standard or other specification in the order. Coatings applied by
electrolysis shall contain a minimum of 99 % zinc.
4.2 Requirements relating to coating on the wire
4.2.1 Coating mass per unit area
The minimum mass of zinc or zinc-aluminium alloy coatings, per unit of surface area of the wire, shall
comply with the requirements of Table 1.
If no class of zinc coating or no coating mass per unit area is specified, the coating shall be called
“regular coating”.
Zinc-coated wire produced as “regular coating” shall have the full surface covered with zinc, but there
is no specified minimum weight of coating.
Coating mass different to Table 1 is possible in agreement between the manufacturer and the supplier.
2 © ISO 2021 – All rights reserved

Table 1 — Coating mass per unit area
Diameter Class
ab
A AB B C D E
d
2 2 2 2 2
g/m g/m g/m g/m g/m
mm
0,15 ≤ d< 0,20 — — 15 — 10
0,20 ≤ d< 0,25 30 20 20 20 15
0,25 ≤ d< 0,32 45 30 30 25 15
0,32 ≤ d< 0,40 60 30 30 25 15
0,40 ≤ d< 0,50 85 55 40 30 15
0,50 ≤ d< 0,60 100 70 50 35 20 40
0,60 ≤ d< 0,70 115 80 60 40 20
0,70 ≤ d< 0,80 130 90 60 45 20
0,80 ≤ d< 0,90 145 100 70 50 20
0,90 ≤ d< 1,00 155 110 70 55 25
1,00 ≤ d< 1,20 165 115 80 60 25
1,20 ≤ d< 1,40 180 125 90 65 25
1,40 ≤ d< 1,65 195 135 100 70 30
1,65 ≤ d< 1,85 205 145 100 75 30
1,85 ≤ d< 2,15 215 155 115 80 40
2,15 ≤ d< 2,50 230 170 125 85 45
2,50 ≤ d< 2,80 245 185 125 95 45
2,80 ≤ d< 3,20 255 195 135 100 50
3,20 ≤ d< 3,80 265 210 135 105 60
3,80 ≤ d< 4,40 275 220 135 110 60
4,40 ≤ d< 5,20 280 220 150 110 70
5,20 ≤ d< 8,20 290 110 80
8,20 ≤ d ≤ 10,00 300 110 80
a
The corrosion resistance in salt spray according ISO 9227 of this Class E shall be at least equivalent of these from a zinc
coating according Class B.
b
only for zinc-aluminium coatings.
4.2.2 Coating requirements to salt-spray test
The surface of the samples of the wires, when tested according ISO 9227, shall not show more than 5 %
dark brown rust after the minimum hours defined below.
The minimum number of hours of salt spray resistance depends on type of coating, wire diameter and
specified minimum coating explained in Table 1.
Table 2 is applicable to wires with minimum 1,6 mm diameter and minimum 100 g/m coating weight.
The minimum number of hours will be calculated by multiplying minimum coating in g/m and the
normalised coefficient (h/g/m ) reported in Table 2.
b
Table 2 — Coating requirements
Normalised coefficient
Coating type
2 a
(h/g/m )
Zinc 2
Standard zinc alu alloy coatings (Zn95Al5) 6
Advanced zinc alu alloy coatings 12
a 2
h/g/m : Multiplied by coating weight = Hours Salt spray before 5 % steel rust according to ISO 9227.
For example: Zinc Class A wire:
—  dia 1,65 with 205 g/m will stand 410 h;
—  dia 10,00 with 300 g/m will stand 600 h.
b
The salt spray test result (e.g. 1 500h ) is the average value of 6 wire samples of each minimum 20 cm length.
4.2.3 Appearance of coating
The coating applied to the wire shall be reasonably smooth and as evenly distributed as industrial
technology allows and not show discontinuities such as bare patches, dross contamination, etc.
NOTE The zinc-aluminium alloy might show difference in colour and become darker with time. This does not
affect the corrosion protection performance.
4.2.4 Dipping test
If agreed at the time of the enquiry and order, the dipping (immersion) test shall be carried out according
to the procedure detailed in 5.3. However, it should be pointed out that there is no direct link between
the number of dips and the coating mass per unit area and that the result is determined as much by the
conditions of manufacture of the coating as by the uniformity of the coating.
Table 3 gives the minimum number of immersions for coatings of Classes A and AB. The dipping test
does not apply to Classes B, C, D and E.
Table 3 — Minimum number of dips
Nominal diameter Class A Class AB
Number of dips Number of dips
d
a b a b
of 1 min of 1/2 min of 1 min of 1/2 min
mm
0,40 ≤ d< 0,60 — 1 — —
0,60 ≤ d< 0,90 1 — — 1
0,90 ≤ d< 1,00 1 1 — 1
1,00 ≤ d< 1,40 1 1 1 —
1,40 ≤ d< 1,65 2 — 1 —
1,65 ≤ d< 1,85 2 — 1 —
1,85 ≤ d< 2,15 2 — 1 1
2,15 ≤ d< 2,80 2 1 1 1
2,80 ≤ d< 4,40 3 — 2 —
4,40 ≤ d< 5,20 3 1 2 —
5,20 ≤ d< 8,20 3 1 — —
8,20 ≤ d ≤ 10,00 4 — — —
a
For Zinc-Alu alloy coatings one dip equals 45 s instead of 1 min.
b
For Zinc-Alu alloy coatings one dip equals 22 s instead of 1/2 min.
4 © ISO 2021 – All rights reserved

4.2.5 Special finishes
If drawing after galvanizing is required, it shall be stipulated at the time of enquiry and order or in the
appropriate product standard. The same also applies for other special finishes such as wax coating, a
polished surfac
...