🔩 Degree of rusting of surfaces coated with paints and varnishes and of duplex systems (metallic plus organic coating) — comparison with pictorial standards Ri 0–Ri 5, in the 2024 edition also white rust (WRi) and percentage of corroded area, PN-EN ISO 4628-3

Materials and NDT PN-EN ISO 4628-3

Overview

WHAT THE STANDARD COVERS. Scope from the PKN catalogue card of PN-EN ISO 4628-3:2025-02, in full (our translation of the Polish card text): “This document specifies a method for assessing the degree of rusting of surfaces coated with paints and varnishes (organic coatings) as well as a metallic coating plus an organic coating (duplex system) by comparison with pictorial standards. The pictorial standards provided in this document show surfaces which have deteriorated to different degrees by a combination of rust broken through the coating and visible under-rusting. The assessment of the degree of rusting according to this document is only an estimation of the area affected by rust on the specimen. Edges are not included.” We do not have the text of the published 2024 edition. We read two final drafts: ISO/FDIS 4628-3:2024 (vote 26.08–21.10.2024; from the cover to Figure 3, page 5: foreword with list of changes, introduction, clauses 1–5.1) and ISO/FDIS 4628-3:2015 — the draft of the 2016 edition (from the cover to the end of Clause 6, with Table 1 and the figures) — and for every piece of content we state which one it comes from.

ACCORDING TO THE DRAFT OF THE 2024 EDITION (foreword, introduction, clauses 1–5.1). The standard was prepared by ISO/TC 35/SC 9 with CEN/TC 139 (Vienna Agreement); the fourth edition replaces the third (ISO 4628-3:2016). Changes according to the foreword: shortened title; updated references; the term “degree of rusting” deleted, “red rust”, “white rust” and “rust traces” added; new Clause 4 with symbols; “rusted area” replaced by “corroded area”; a note on the original size of the figures; a new Table 1 for designating the size of rusting; corrected percentage of corroded area in Figure A.5; assessment of white rust with new pictorial standards added; assessment by estimating the percentage of corroded area added; new item d) in the test report — the method used (1 or 2); new Annex B with an example of a panel after the neutral salt spray (NSS) test according to ISO 9227 with degree Ri 4; the former Annex B became C, and the correlation with the ASTM scale was adjusted to ASTM D610-08. Introduction: the red rust pictorial standards were selected from the CEPE “European rust scale” (correlation in Table C.1), correlation with ASTM D610-08 — in Table C.2. Scope as on the PKN card. Normative references: ISO 4618 (vocabulary) and ISO 13076 (lighting and procedure for visual assessment). Definitions: red rust — corrosion products on ferrous substrates (iron, steel), generally porous, brittle or powdery; white rust — corrosion products on non-ferrous substrates (zinc, aluminium), metal hydroxides and oxides formed in humid conditions; rust traces — contamination by bleeding corrosion products. Symbols: R, Ri, R% (red rust — pictorial standards, percentage), WR, WRi, WR% (white rust), NSS. Table of contents: 5 — assessment of red rust, method 1 (pictorial standards Ri) and method 2 (percentage R%); 6 — assessment of white rust, method 1 (WRi) and method 2 (WR%); 7 — expression of results; 8 — test report; Annex A (normative) — calibration images; B (informative) — example after NSS; C — correlation with other systems. Subclause 5.1: the degree of red rust is assessed with the pictorial standards Ri in Figures 1–5; the original pictures are only examples of organic coated steel surfaces after natural weathering and do not show the reactions after short corrosion tests (example after NSS — Annex B); rust traces are not assessed; viewed in A4 format the photographs are in original size for comparison.

ACCORDING TO THE DRAFT OF THE 2016 EDITION (ISO/FDIS 4628-3:2015, clauses 1–6). Scope: assessment of the degree of rusting of coatings by comparison with pictorial standards of coated steel surfaces (rust broken through the coating plus visible under-rust); notes: correlation with the “European rust scale” and with ASTM D 610 in Annex B; rust on uncoated steel is designated according to ISO 8501-1 (grades A, B, C, D); designation system — ISO 4628-1. The 2016 edition changed against 2003 among others: it added the reference to ISO 13076 and a note on the area of degree Ri 5. Assessment (Clause 4): the degree Ri is assessed with the pictorial standards in Figures 1–5; the approximate rusted area (rust broken through plus visible under-rust) according to Table 1: Ri 0 — 0 %, Ri 1 — 0,05 %, Ri 2 — 0,5 %, Ri 3 — 1 %, Ri 4 — 8 %, Ri 5 — 40 % to 50 % (footnote: the area measured in Figure A.5 is only about 35 %, the visual impression from Figure 5 — 40 % to 50 %, among other reasons because partly delaminated rust flakes are not distinguished from other areas; the standard considers this negligible because Ri 5 is normally outside any specification). Invisible under-rust is assessed, if required, by a procedure agreed between the parties; with different degrees in different parts each is given with the part concerned; assessment under good lighting according to ISO 13076; when the average size of rust spots differs considerably from the standards, it may be given according to ISO 4628-1:2015, Table 2; the pictorial standards are basically intended for coated steel — they may be used for coated non-ferrous metals if the form of breakdown is comparable; with assessment by an optical imaging system the system is calibrated with the images in Annex A. Result (5): Ri class, possibly divided by parts of the area and with the numerical size of spots, e.g. for Ri 3 and spots from 0,5 mm to 5 mm: “rusting; degree of rusting Ri3 (S4)”. Test report (6): identification of the coating, reference to ISO 4628-3, type, size and location of the surface examined, result, lighting, anomalies, date.

STATUS (cards as of 02.10.2026). The card of PN-EN ISO 4628-3:2025-02 (English version) has no “Withdrawn” header — this edition is CURRENT: published 20-02-2025, 36 pages, price group R, Chemistry Sector, KT 175 for Paints and Varnishes, ICS 87.040, “Introduces: EN ISO 4628-3:2024 [IDT], ISO 4628-3:2024 [IDT]”, “Replaces: PN-EN ISO 4628-3:2016-03 - English version”. There is no Polish version of the 2025 edition in the catalogue: the PKN search for “PN-EN ISO 4628-3” (02.10.2026) shows five items — PN-ISO 4628-3:1999 (Polish), PN-EN ISO 4628-3:2004 (English), 2005 (Polish), 2016-03 (English) and 2025-02 (English). Card of PN-EN ISO 4628-3:2016-03 (English version): “Withdrawn and replaced by PN-EN ISO 4628-3:2025-02 - English version”, withdrawal date 20-02-2025; card of PN-EN ISO 4628-3:2005 (Polish version): withdrawn 09-03-2016, replaced by 2016-03. What the change from 2016 to 2025 means for the result: according to the foreword of the FDIS — a second method (percentage of corroded area), assessment of white rust, a table of rust size, corrected percentage in Figure A.5 and the obligation to state the method in the report; the values of the new Table 1 and the white rust pictorial standards are NOT GIVEN. Card of PN-EN ISO 4628-1:2016-03 (English version; general introduction and designation system): no “Withdrawn” header. We have not checked the status of ISO 4628-3:2024 on the ISO website or the status of ASTM D610.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, data up to 17.09.2026, read 02.10.2026). The number 4628-3 appears in 9 records of 9 laboratories: AB 023, AB 089, AB 128, AB 163, AB 369, AB 1424, AB 1552, AB 1631, AB 1700. Current scopes on the PCA website (read 02.10.2026, scope issues from 16.07.2025 to 01.09.2026): one line with the number at each. Editions in PCA: 2025-02 — AB 089, AB 163, AB 1424, AB 1631, AB 1700; 2016-03 (withdrawn) — AB 1552; without date — AB 023, AB 128, AB 369. None of these items is suspended (at AB 1700 the footnote on the suspension of part of the scope concerns lines in bold italics — the lines with 4628-3 are not set that way; at AB 023 the word “suspension” refers to a product — “suspension systems”). The “Laboratories” tab searches for entries BEGINNING WITH “PN-EN ISO 4628-3” and shows all 9 laboratories — checked with the tab query on the production server labcoda.pl on 02.10.2026: 9 (under “EN ISO 4628-3” and “ISO 4628-3” — 0).

WHAT THE LABORATORIES ASSESS (items in PCA). Object: coating products for the protection of metal elements (AB 023 — “visual method also in situ”), metals and alloys, plastics, composites and polymers, organic and inorganic paint coatings (AB 089), organic and inorganic coatings and metal products (AB 128 — next to ASTM D610), coatings (AB 163), paint systems and anti-corrosion coatings (AB 369), metallic coatings and paint systems on metal substrates (AB 1424), construction products and materials, builders’ hardware, parts of machines and electrical equipment, including mining equipment (AB 1552), paint systems on metal substrates (AB 1631), organic and inorganic coatings (metallic, oxide) on ferromagnetic and non-ferromagnetic substrates (AB 1700). At eight laboratories (all except AB 1631) the number stands in one item or in a block of items with other parts of the ISO 4628 series (assessment of blistering, cracking, flaking, chalking, delamination around a scribe, filiform corrosion) — at AB 163, AB 369, AB 1424, AB 1552 and AB 1700 together with PN-EN ISO 4628-1 as the designation system (edition 2016-03, at AB 369 without date); the scopes of AB 1424, AB 1552 and AB 1700 also contain salt spray or cyclic corrosion tests, after which the degradation of coatings is assessed. Assessment of the degree of blistering according to PN-EN ISO 4628-2 has a separate entry in the Knowledge Base.

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. With the object: the Ri pictorial standards show organic coated steel after natural weathering — they do not show the appearance after short corrosion tests (an example after NSS only in Annex B of the 2024 edition); rust on uncoated steel is not assessed by this standard (according to the 2016 draft — ISO 8501-1), and metallic coatings without an organic coating are, according to the “Scope” clause of the 2024 edition, not within it (organic coatings and duplex systems) — in the scopes this standard is cited for “metallic coatings” (AB 1424) and “inorganic coatings (metallic, oxide)” (AB 1700); corrosion products of zinc and aluminium are white rust, which the 2024 edition assesses on a separate WRi scale, not on the Ri scale. In the assessment: edges are not assessed, nor are rust traces (2024 edition); invisible under-rust is not included in Ri without a separate, agreed procedure; lighting according to ISO 13076; the figures are compared in original size (A4 print) — a reduced print changes the impression of the area. With the result: Ri is a class from comparison, not a measurement of area — according to the draft of the 2016 edition, for Ri 5 the visual impression (40–50 %) and the measurement in Figure A.5 (approx. 35 %) differed; according to its foreword the 2024 edition corrected the percentage of the corroded area in Figure A.5 — the new value is not known to us; a result according to the 2024 edition must state the method (1 — pictorial standards, 2 — percentage), and R% and Ri are different quantities; a laboratory citing the 2016-03 edition (AB 1552) or the number without date (AB 023, AB 128, AB 369) may use a different rust size scale and have no white rust assessment; the correlation with ASTM D610 changed in the 2024 edition (adjusted to ASTM D610-08), so converting Ri to the ASTM scale according to the old edition may give a different number.

WHAT WE DO NOT GIVE. From the 2024 edition we do not have subclause 5.2 (percentage method), Clauses 6–8 (white rust, expression of results, test report — apart from the changes listed in the foreword), the new Table 1 (size of rusting) or Annexes A–C (calibration images, example after NSS, correlation tables); we do not know whether the area percentages for Ri 0–Ri 5 changed — we give them from the draft of the 2016 edition. We do not give the content of ISO 4628-1 (designation system, size scale S) or ISO 13076.

Method principle

The coated surface is assessed visually, under lighting according to ISO 13076, by comparison with pictorial standards: for red rust on steel — classes Ri 0 to Ri 5, corresponding according to the 2016 edition to approx. 0 %, 0,05 %, 0,5 %, 1 %, 8 % and 40–50 % rusted area (rust broken through the coating plus visible under-rust); edges are not assessed. The 2024 edition added the assessment of white rust on non-ferrous substrates (WRi) and a second method — estimating the percentage of corroded area (R%, WR%) — with the obligation to state the method used.

Applications

• Assessment of paint coatings and paint systems on metal substrates after corrosion tests (salt spray, cyclic corrosion conditions) and natural exposure — 9 laboratories
• On-site (“in situ”) assessment of coating products for the protection of metal elements — AB 023
• Duplex systems (metallic plus organic coating) — within the scope of the 2024 edition

Key parameters

Standard

Standard number

PN-EN ISO 4628-3:2025-02 (wersja angielska; EN ISO 4628-3:2024, ISO 4628-3:2024 IDT)

Title (PL)

Farby i lakiery — Ocena ilości i rozmiaru uszkodzeń oraz intensywności jednolitych zmian w wyglądzie — Część 3: Ocena stopnia zardzewienia

Title (EN)

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

Step-by-step procedure

1. Preparing the assessment

   Surface after a corrosion test or exposure; edges excluded from the assessment; lighting according to ISO 13076. PN-EN ISO 4628-3:2025-02 current (card as of 02.10.2026).

2. Red rust — pictorial standards

   Comparison with Figures 1–5 and assignment of class Ri 0–Ri 5; rust traces (bleeding) are not assessed; with different degrees in different parts — each degree with its part of the area.

3. Percentage method and white rust

   2024 edition: estimating the percentage of corroded area (R%) and assessment of white rust on non-ferrous substrates (WRi, WR%) — details of subclauses 5.2 and 6 NOT GIVEN.

4. Spot size

   When the spot size differs considerably from the standards — adding the size class according to ISO 4628-1 (in the 2024 edition — Table 1 of rust size, values NOT GIVEN).

5. Result and report

   Ri class (possibly with size, e.g. Ri3 (S4)); according to the 2024 edition also the method used (1 or 2); identification of the coating, surface, lighting, anomalies, date.

Required equipment and apparatus

Health and safety (OHS)

• Visual assessment — the read text of the standard contains no health and safety warnings; hazards come from the preceding corrosion tests (salt cabinets, solutions) according to their standards
• TECHNICAL NOTE: Ri is a class from comparison with a standard, not an area measurement; white rust (zinc, aluminium) has a separate WRi scale in the 2024 edition; AB 1552 cites the 2016-03 edition, withdrawn 20-02-2025

Frequently asked questions