🔩 Assessment of the resistance of metals and alloys, metallic and non-organic coatings and organic coatings to a humid atmosphere containing sulfur dioxide — hermetic cabinet (300 ± 10) l with (2,0 ± 0,2) l of water at the bottom, single dose of 0,2, 1,0 or 2,0 l of SO2 from a cylinder at the start of the cycle, (40 ± 3) °C and humidity about 100 %; cycle of 24 h in SO2 (method A) or 8 h in SO2 and 16 h in standard atmosphere (method B), specimen area (0,5 ± 0,1) m², recommended 1–20 cycles, PN-EN ISO 22479

Materials and NDT PN-EN ISO 22479

Overview

WHAT THE STANDARD COVERS. Scope from the PKN catalogue card of PN-EN ISO 22479:2022-12 (English version; scope in Polish on the card), in full (our translation of the Polish card text): “This document specifies a method for assessing the resistance of materials or products to a humid atmosphere containing sulfur dioxide. This method applies to testing metals and alloys, metallic and non-organic coatings and organic coatings.” We read the text of the standard in the preview of ISO 22479:2019 from the cover to clause 7.2 (page 5); we do not have the test procedure (Clause 8), evaluation, the test report or Annexes A–C.

ACCORDING TO THE TEXT OF ISO 22479:2019 (foreword, introduction, Clauses 1–7.2). The standard was prepared by ISO/TC 156 (corrosion of metals and alloys). The first edition replaces ISO 3231:1993 and ISO 6988:1985, which were combined and revised; main change: the generation of sulfur dioxide from reagents was deleted because of the risk of exposure to toxic chemicals. Introduction: a humid atmosphere containing SO2 induces corrosion of many metals; the results should not be regarded as a direct measure of corrosion resistance in all service environments or as a measure of the relative corrosion resistance of different materials in service; only the same corrosion protection systems should be tested at the same time in one test, because interaction between specimens cannot be excluded; “fixed gas method” means that at the start of the test a fixed volume of gas is introduced into a cabinet of fixed volume. Scope (Clause 1, as on the card). References: ISO 1514 (standard panels for paints), ISO 2808 (film thickness), ISO 8044 (corrosion terms). Principle (Clause 4): specimens are exposed to a humid atmosphere containing SO2; sulfur dioxide dissolved in the moisture condenses on the surface and causes corrosion. Apparatus (Clause 5): components in contact with SO2 of corrosion-resistant materials not emitting gases or vapours; cabinet — preferred capacity (300 ± 10) l (other by agreement of the parties, with proportional selection of specimens, gas volume and quantity of water); upper part shaped so that drops of condensate do not fall on the specimens (inclination of about 12° or more); specimens may be placed at different levels, provided they do not drip onto lower ones; temperature controlled by heating the floor and lower part of the walls, measured at least 250 mm from the side walls and at least 150 mm below the lid; gas inlet less than 50 mm above the water surface; hermetic cabinet with a pressure relief valve in the upper part and a drain port; exhaust gases must be treated appropriately; Figure 1 — typical cabinet (lid, specimens, supports, water, gas inlet, flowmeter, SO2 source, water tank, heater, drain, valve, temperature measurement), Figure A.1 — another example; the cabinet in a room free from dust, draughts, corrosive gases and direct sunlight, at (23 ± 5) °C and a relative humidity below 75 %. SO2 source (5.3): cylinder with a volume concentration above 99,9 %, with regulating and measuring apparatus, volume measured with a calibrated flowmeter; another instrument measures the volume by squeezing out viscous liquid paraffin for 0,2, 1,0 and 2,0 l. New cabinet (5.4): at least one cycle according to 8.2–8.5 without specimens, according to Table 1, with 2,0 l of SO2. Specimens (Clause 6): number, type, roughness, coating thickness, shape and dimensions according to the product specification or agreement; typically 150 mm × 100 mm with a thickness of 0,75–1,25 mm; metals — thorough cleaning without agents attacking the surface and without recontamination; specimens cut from a larger article — without damaging the coating, edges protected (e.g. with wax or tape); paints — panels according to ISO 1514, back and edges also coated, drying (curing) and conditioning for at least 16 h at (23 ± 2) °C and (50 ± 5) % RH, coating thickness non-destructively according to ISO 2808. Arrangement (6.4): distance between specimens at least 20 mm, from the walls at least 100 mm, lower edge more than 200 mm above the water; specimens must not shield each other; contact with supports as small as possible; orientation from vertical to (15 ± 2)° from vertical, main surface upwards (assemblies and enclosures — preferably as in use); total specimen area (0,5 ± 0,1) m² for each (300 ± 10) l (for other capacities proportionally); smaller — substitute specimens of the same material, because absorption of SO2 depends on the material. Conditions (7.1): 24 h cycle — method A: 24 h in SO2; method B (when temperature and humidity strongly affect the specimens): 8 h in SO2 and 16 h in standard atmosphere; metallic and non-organic coatings — 0,2 l of SO2; paints — 0,2 or 1,0 l; 0,2 l is generally recommended for coatings up to about 40 µm; 2,0 l — by agreement or according to the product specification, e.g. for corrosion-resistant coatings (hard chromium, anodic coating); Table 1 (method A): (40 ± 3) °C, humidity about 100 %, SO2 0,2, 1,0 or 2,0 l, water (2,0 ± 0,2) l per (300 ± 10) l of capacity; Table 2 (method B): 8 h — conditions as in method A, 16 h — (23 ± 5) °C, humidity below 75 %; note 1: theoretical concentrations at the start of the cycle are 0,067 %, 0,33 % and 0,67 %, but much SO2 quickly dissolves in the water at the bottom and the actual concentration in the cabinet is much lower (Figure C.1); note 2: the temperature tolerance is the permitted fluctuation around the set point at equilibrium, not freedom to choose the set point. Duration (7.2): according to the product specification or agreement; the test may be ended when a specified degree of corrosion is reached or appearance or function deteriorates unacceptably; recommended numbers of cycles: 1, 2, 5, 10, 15 or 20; this is where the part we read ends.

STATUS (cards as of 02.10.2026). The card of PN-EN ISO 22479:2022-12 (English version, published 05-12-2022, 28 pages, price group N) has no “Withdrawn” header: Metallurgy Sector, KT 106 Corrosion and Corrosion Protection of Metallic Materials, ICS 77.060, “Introduces: EN ISO 22479:2022 [IDT], ISO 22479:2019 [IDT]”, “Replaces: PN-EN ISO 6988:2000 – Polish version, PN-EN ISO 3231:2000 – Polish version”. The PKN search for “PN-EN ISO 22479” (02.10.2026) shows only this edition.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, data up to 17.09.2026, read on 02.10.2026). The number 22479 appears in 9 records at 7 laboratories: AB 023, AB 044, AB 089, AB 128, AB 207, AB 1424, AB 1690. In the current scopes on the PCA website (read on 02.10.2026, issues from 16.07.2025 to 08.07.2026) the number appears at all 7: “PN-EN ISO 22479:2022-12” at AB 089, AB 207, AB 1424, and at AB 044 and AB 1690 together with EN ISO 22479:2022 and ISO 22479:2019 (AB 1690 in two items); without the year at AB 128 and AB 023, which in a second item writes “PN-EN 22479” (without “ISO”). The replaced standards still stand next to it: PN-EN ISO 3231:2000 at AB 044 (separate row, with EN ISO 3231:1997 and ISO 3231:1993) and AB 1424 (in the same row, together with PN-EN 13523-23:2024-03), PN-EN ISO 6988:2000 at AB 207 (separate row). No row is set in bold italics. The “Laboratories” tab searches for entries BEGINNING WITH “PN-EN ISO 22479” and shows all 7 laboratories — checked with a query of the tab on the production server labcoda.pl on 02.10.2026.

WHAT THE LABORATORIES TEST (items in the PCA scopes). Metals and alloys, metallic, non-organic and organic coatings, paints and paint systems, plastic products (AB 023, AB 128), plastics and composites (AB 089), maritime navigation and radiocommunication equipment (AB 207), connectors — “climatic test group D” according to PN-EN 61984 (AB 1690); property — “resistance to a humid atmosphere containing SO2/sulfur dioxide” (AB 023, AB 1424), “sulfur dioxide test in a humid atmosphere (fixed gas method)” (AB 044), “test in an atmosphere saturated with sulfur dioxide (Kesternich test)” (AB 1690), “corrosion resistance in a sulfur dioxide atmosphere with condensation of moisture” (AB 128).

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. Volume of SO2: 0,2 l, 1,0 l and 2,0 l are three different exposures — a result without the stated volume (and method A or B) is not comparable. Concentration: the theoretical 0,067–0,67 % at the start of the cycle is not the actual concentration — SO2 quickly dissolves in the water at the bottom. Cabinet loading: total area (0,5 ± 0,1) m² per 300 l; with less, substitute specimens of the same material must be added, because absorption of SO2 depends on the material and the result may change. Mixing specimens: only the same protection systems in one test — specimens affect each other. Arrangement: from vertical to 15° from vertical, spacing 20 mm between specimens and 100 mm from the walls, more than 200 mm above the water; dripping from upper specimens onto lower ones is not permitted. New cabinet: the first cycle without specimens with 2,0 l of SO2. Edition: ISO 3231 and ISO 6988 were replaced and the generation of SO2 from reagents was deleted — PN-EN ISO 3231:2000 and 6988:2000, still listed next to 22479 (AB 044, AB 1424, AB 207), are replaced standards.

WHAT WE DO NOT GIVE. We do not have Clause 8 (sequence of operations in the cycle, water renewal), evaluation of results, the test report or Annexes A–C — so we do not give the way of renewing water and gas between cycles or criteria for assessing corrosion.

Method principle

Specimens in a hermetic cabinet with water at the bottom are exposed to a humid atmosphere (about 100 % RH, 40 °C) with a fixed volume of SO2 introduced once; sulfur dioxide dissolved in the condensing moisture causes corrosion, and the test is repeated in 24-hour cycles (method A or B).

Applications

• Metals and alloys, metallic, non-organic and organic coatings (paints, paint systems) — 7 laboratories in the PCA scopes
• Plastic products, connectors and electronic equipment (e.g. climatic test group D according to PN-EN 61984, AB 1690)
• Corrosion-resistant coatings — hard chromium, anodizing (2,0 l of SO2 by agreement)

Key parameters

Standard

Standard number

PN-EN ISO 22479:2022-12 (wersja angielska; EN ISO 22479:2022 IDT, ISO 22479:2019 IDT)

Title (PL)

Korozja metali i stopów — Próba z ditlenkiem siarki w wilgotnej atmosferze (metoda ustalonej objętości gazu)

Title (EN)

Corrosion of metals and alloys — Sulfur dioxide test in a humid atmosphere (fixed gas method)

Step-by-step procedure

1. Specimens

   Dimensions according to specification (typically 150 × 100 mm); metals cleaned, paints on panels according to ISO 1514, conditioned ≥ 16 h. PN-EN ISO 22479:2022-12 current (cards as of 02.10.2026).

2. Arrangement

   Vertical to (15 ± 2)° from vertical, spacing ≥ 20 mm, ≥ 100 mm from walls, > 200 mm above water; total area (0,5 ± 0,1) m² (substitute specimens of the same material).

3. Filling and dose

   (2,0 ± 0,2) l of water, closing the cabinet, introduction of 0,2, 1,0 or 2,0 l of SO2 from the cylinder through the flowmeter.

4. Cycle

   Method A — 24 h at (40 ± 3) °C and RH about 100 %; method B — 8 h in SO2 and 16 h in standard atmosphere; sequence of operations according to Clause 8.

5. Duration and end

   Number of cycles according to specification (recommended 1, 2, 5, 10, 15, 20) or until a specified degree of corrosion or deterioration of appearance or function is reached.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• The standard (5.3) warns: sulfur dioxide (CAS 7446-09-5) is toxic, corrosive and irritating; handling only by skilled personnel or under their control; exhaust gases and gas from the pressure relief valve must be treated
• TECHNICAL NOTE: the result depends on the SO2 dose (0,2 / 1,0 / 2,0 l), the method (A or B) and the cabinet loading (0,5 m² per 300 l); the theoretical SO2 concentration is not the actual concentration

Frequently asked questions