TECHNICAL STANDARD
ISO 4628-3
Paints and varnishes — Evaluation of quantity and size of defects, and of intensity of uniform changes in appearance — Part 3: Assessment of degree of rusting
ISO
2024
Current
WHAT DOES THIS STANDARD COVER?
ISO 4628-3 provides a method for assessing the degree of rusting present on coated surfaces using recognised reference criteria.
WHY IS IT RELEVANT?
Particularly relevant to protective coating condition surveys of steel infrastructure where the distribution and extent of visible corrosion needs to be recorded consistently. Rusting assessment can support corrosion mapping and maintenance planning, but the rating alone does not determine substrate loss, structural condition or root cause.
KEY INSPECTION CONSIDERATIONS
The standard addresses assessment of the degree of rusting of coated surfaces. Visible rusting should be assessed consistently and distinguished, where possible, from unrelated surface staining or deposits. Suitable inspection access and viewing conditions are important when recording coating condition.
WHAT THE STANDARD SHOULD NOT BE USED TO ASSUME
A rusting assessment records visible coating condition but does not independently establish the cause of corrosion. Corrosion can be influenced by multiple factors, including coating breakdown, damage, environment and detailing. The assessment does not reveal the condition of every area beneath apparently intact adjacent coating.
PRACTICAL INSPECTION APPLICATION
During coating condition surveys, inspectors can record the extent and location of visible rusting and retain representative photographs. Areas of deterioration can then be considered alongside other defects, exposure conditions and structural details when developing a wider understanding of coating condition.
RELATED TECHNICAL STANDARDS
RELATED TECHNICAL TOPICS
Condition Assessment Rusting Corrosion Corrosion Mapping Steel Coatings
RELATED PIL GUIDANCE
A pre-condition coating survey brings visual inspection, testing, sampling and access planning together to support evidence-based maintenance decisions.
A structured approach to investigating protective coating failure through evidence, testing, sampling and project-record review.
RELATED EXPERTISE
Condition Surveys Coating Inspection Testing & Analysis Technical Consultancy
ABOUT THIS TECHNICAL SUMMARY
Paint Inspection Ltd provides this information to help inspectors, engineers, asset owners and contractors understand the practical relevance of commonly referenced protective coatings standards. This page is PIL technical guidance and does not reproduce or replace the published standard. Users should refer to the current published standard, project specification, coating manufacturer requirements and other applicable contract documents when establishing project requirements or acceptance criteria.
PIL TECHNICAL ASSISTANT
Ask the PIL Technical Assistant about this standard and related coating inspection topics.
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OFFICIAL STANDARD
PIL technical summaries are intended to explain the inspection relevance of industry standards and do not replace the published document.
STATUS AND SOURCE VERIFICATION
Standard number, edition, title and current publication status checked against the official ISO catalogue in September 2026. ISO 4628-3:2016 is withdrawn/superseded and is not linked.