ISO 3651 — Standard

About the Standard

Scope title: intergranular corrosion resistance of stainless steels

ISO 3651 is a standard published by International Organization for Standardization (ISO). The international standards organisation; it publishes the widest body of management system, test method and product standards.

See the other 310 codes from ISO

Coverage areas

Corrosion Tests — What Does This Testing Field Cover?

The section below describes the field that code ISO 3651 belongs to; it is not the text of the standard or the regime itself. The scope title of the code is given above, and technical requirements are shared at the quotation stage.

Corrosion testing assesses under accelerated conditions how long metals and coatings last in a corrosive environment. The family contains two approaches, and the difference between them is the most important knowledge in the field: constant-condition tests and cyclic tests.

Constant-condition salt spray (ASTM B117, ISO 9227) maintains the same environment in the chamber throughout: the same salt concentration, the same temperature, a continuously wet surface. The strength of this approach is its REPEATABILITY; because the conditions are tightly defined, results from different laboratories come out close to one another. That is exactly the property wanted when monitoring production consistency and comparing suppliers.

But the real atmosphere is not constant. A surface gets wet, dries, warms, cools, takes UV and becomes soiled. The wet-dry cycle changes the corrosion mechanism: during drying the salt concentrates, oxygen access increases and corrosion accelerates. The form of damage on a continuously wet surface differs from that on a cyclically wetted one.

Cyclic tests (SAE J2334, VDA 233-102, ASTM G85, ISO 16701) imitate this variability and give results closer to the damage patterns seen in the field. The automotive sector has largely moved to this approach. The practical consequence is this: the same two coatings may RANK DIFFERENTLY in constant and cyclic tests; which test was applied determines the result.

No test in this family defines a DURATION OR ACCEPTANCE CRITERION. How many hours it is applied for and what level of damage is acceptable come from the product standard or the customer specification. The assessment scales are defined in separate standards: different scales are used for degree of rusting, blistering, creep from a scribe and loss of adhesion.

The damage looked for varies with the coating type. For metallic coatings, white rust (corrosion of the coating itself) and red rust (corrosion reaching the base metal) are reported separately, and specifications usually give a separate duration for each. On painted surfaces, creep from a scribe and blistering come to the fore.

Electrochemical methods are a separate body of work and answer a different question. Potentiodynamic polarisation, electrochemical impedance spectroscopy and pitting potential measurements reveal the MECHANISM and rate of corrosion within hours; chamber tests give the result visually over weeks. The two are complementary rather than alternatives.

Stainless steels have a special sub-body in the field: pitting and crevice corrosion and intergranular corrosion tests indicate the quality of the heat treatment and the condition after welding.

Method groups in this field

Constant-condition salt spray
ASTM B117 and ISO 9227 (NSS); for repeatable comparison and process control.
Acidified and accelerated
The AASS and CASS conditions of ISO 9227; preferred for decorative chromium-nickel coatings.
Cyclic corrosion
SAE J2334, VDA 233-102, ASTM G85 and ISO 16701; approaches field behaviour through wet-dry cycles.
Humidity and condensation
Steady damp heat, condensation and cyclic humidity tests; these reveal coating blistering.
Electrochemical
Polarisation, impedance spectroscopy, pitting and crevice corrosion potential measurements.
Stainless steel specific tests
Pitting and crevice corrosion, intergranular corrosion; indicators of heat treatment and weld quality.
Assessment scales
Scales for degree of rusting, blistering, creep from a scribe and loss of adhesion; the ratings come from these standards.

Commonly confused in this field

Chamber hours cannot be converted into field life; there is no reliable conversion factor.
Constant and cyclic tests can produce different rankings; whichever the specification states is the one applied.
A corrosion report without a stated duration and acceptance criterion cannot be interpreted.
If the coating thickness is not reported, the result cannot be compared; thickness directly affects durability.
White rust and red rust say different things; the two must be reported separately.
The position and angle of the specimen in the chamber affect the result; standards govern this and the report must document it.

Which decisions these results support

Selection of the coating system and supplier approval
Process control of the coating line and lot acceptance
Evidence of durability for automotive and outdoor products
Assessment of field corrosion damage and warranty decisions
Verification of heat treatment and weld quality in stainless steel

Structure of the Code

Published by: ISO
Serial number: 3651
Part: without partition

Codes in the library without release year is kept. The current version changes over time; If the year is specified in your specification, that version is taken as basis, if not specified, the most current version is applied.

Scope

Related Tests and Services

A separate test page based on this code has not yet been released. The code falls within the scope of the following test families.

Technical Requirements

Standard texts are copyright of the relevant organization; test condition, sample and acceptance criteria cannot be fitted here.

Technical requirements specific to your product, once we clarify the scope At offer stage shared in writing.

Relevant Product Groups and Legislation

This code is included in the standard tag of the product pages below.

These product pages carry notes for the following markets: European Union, United Kingdom, USA. Whether the standard is mandatory in the relevant market varies depending on the product group and the applicable legislation.

Regulations published with this code on the same product pages:

(AB) 2018/858Vehicle Type-Approval FrameworkApproval of motor vehicles and their components. Component and separate technical unit approval run under this framework; the E mark arises from it.
UNECEUNECE 1958 AgreementType-approval under component-specific UNECE regulations (e.g. R10 EMC, R30/R54 tyres, R43 glazing).
UNECE R10UNECE R10Electromagnetic compatibility approval for vehicles and their components.
2011/65/EURoHSRestriction of hazardous substances in electrical and electronic equipment.
2000/53/ATELVEnd-of-life vehicles. Sets heavy-metal restrictions and recoverability targets.
(EU) 2017/745MDRThe Medical Device Regulation. Classification (I, IIa, IIb, III), clinical evaluation, technical documentation and post-market surveillance obligations; the notified body's role grows as the class rises.
(EU) 2017/746IVDRThe In Vitro Diagnostic Medical Devices Regulation. In vitro diagnostic devices fall under this regulation instead of the MDR.
(AB) 2017/745 art. 33EUDAMEDThe European medical device database. From 28 May 2026, the actor registration, UDI/device, certificate and market surveillance modules are mandatory; placing on the market is not possible without a valid SRN.
2006/42/ATMachinery Directive (overlap)Relevant essential requirements also apply to medical devices that also qualify as machinery.
(EC) 1907/2006REACHRegistration, evaluation, authorisation and restriction of chemicals; SVHC notification.
(EU) 2023/1230Machinery RegulationReplaces 2006/42/EC and becomes mandatory on 20 January 2027 with no further transition period. Requires notified-body involvement for Annex I high-risk machinery.
2014/35/EULVDThe Low Voltage Directive. Governs electrical safety in the 50–1000 V AC range.
2014/30/EUEMCThe Electromagnetic Compatibility Directive. Emission and immunity are covered together.
2014/34/ABATEXEquipment and protective systems used in explosive atmospheres. The category and conformity route are determined by zone classification.
2000/14/ATNoise EmissionNoise emitted into the environment by outdoor equipment. Machinery within scope requires a sound-power-level declaration and marking.
2014/68/EUPEDThe Pressure Equipment Directive for pressurised parts; the category is determined by pressure and volume.
(EU) 2024/573F-GasRefrigerant type, GWP value and leak-tightness obligations for systems containing a refrigerant.
(AB) 547/2012Ecodesign (water pumps)Ecodesign requirements for water pumps. Sets minimum efficiency index and product-information requirements.
(AB) 2019/1781Ecodesign (electric motors)Efficiency class requirements for electric motors and variable-speed drives.
(AT) 1935/2004Food Contact MaterialsGeneral requirements for equipment in contact with food; material conformity is required for valves in food lines.
(AB) 2020/2184Drinking Water Contact ProductsHygiene requirements for materials in contact with water under the Drinking Water Directive.
2014/29/ABSimple Pressure VesselsA separate directive for series-produced simple pressure vessels; its scope must be distinguished from the PED.
2010/35/ABTransportable Pressure EquipmentThe pi mark and periodic inspection regime for transportable pressure equipment.
2009/48/ECToy SafetyThe Toy Safety Directive. Regulates mechanical, physical, flammability, chemical and electrical safety requirements together; a technical file and safety assessment are mandatory.
EN 62115Electrical toysSafety for electric toys; applies to mains-connected or battery-powered toys.
(AT) 1907/2006 Annex XVII item 51-52Phthalate RestrictionRestriction of certain phthalates in toys and childcare articles.
(EU) 2023/1542Batteries RegulationBattery obligations and a removability requirement for toys containing a battery.
(AB) 1007/2011Textile LabellingTextile fibre names and labelling. Declaration of fibre composition and regulation of the label language.
(AT) 1907/2006 Annex XVII item 43Azo Dye RestrictionRestriction of certain azo dyes in textiles in contact with skin.
(AB) 2019/1021PFAS / PFOA RestrictionRestriction of PFOA and its derivatives under the Persistent Organic Pollutants Regulation.
(EU) 2023/988GPSRThe General Product Safety Regulation. The safety framework for consumer products not covered by sector-specific legislation.
(EU) 2016/425Personal Protective Equipment (overlap)The PPE Regulation's scope and category are determined for textiles with a protective function.
(AB) 10/2011Plastics in Food ContactPlastic materials in contact with food. The list of authorised substances, and overall and specific migration limits.
(AT) 2023/2006Good Manufacturing PracticeGood manufacturing practice (GMP) for food-contact materials.
(AB) 2025/40Packaging and Packaging WasteThe Packaging and Packaging Waste Regulation. Recyclability, recycled-content and packaging-reduction obligations; replaces 94/62/EC.
(AB) 2022/1616Recycled PlasticRecycled plastic materials in contact with food.
(EU) 2024/3110Construction Products RegulationDeclaration of performance and CE marking for construction products. Most provisions apply from 8 January 2026; it progressively replaces (EU) 305/2011.
(AB) 305/2011CPR (transition)Continues to apply during the transition period for product groups where a new harmonised standard has not been published.
EN 13501-1Reaction-to-Fire ClassificationReaction-to-fire class for construction products; a mandatory item of the declaration of performance.
(EU) 2023/1115Deforestation (wood-based)A deforestation-free supply declaration for wood and derived construction materials.
(AT) 1223/2009Cosmetic Products RegulationThe Cosmetic Products Regulation. Appointing a responsible person, the product information file (PIF), the safety assessment (CPSR) and CPNP notification are mandatory; there is no product approval, and responsibility rests with the manufacturer.
(AT) 1223/2009 Annexes II-VIProhibited and Restricted SubstancesLists of prohibited substances, restricted substances, and permitted preservatives, colorants and UV filters.
(AT) 1223/2009 art. 16Nanomaterial NotificationA separate notification six months before placing on the market for products containing nanomaterials.
(AT) 1223/2009 art. 18Animal Testing BanA ban on animal testing of finished products and ingredients, and on placing animal-tested products on the market.
(AT) 178/2002General Food LawThe general principles of food law, traceability and food safety responsibility.
(AT) 852/2004Food HygieneHygiene rules for food businesses and the obligation for a HACCP-based system.
(AB) 1169/2011Food Information to ConsumersFood labelling; nutrition declaration, allergen information and origin information.
(AB) 2023/915ContaminantsMaximum levels of contaminants in food.
(AT) 396/2005Pesticide residuesMaximum residue limits in food of plant and animal origin.
(AT) 2073/2005Microbiological CriteriaMicrobiological criteria for foodstuffs.

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