ISO 7989-2:2021

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)