Overview
EN ISO 7441:2015 (ISO 7441:2015) - "Corrosion of metals and alloys - Determination of bimetallic corrosion in atmospheric exposure corrosion tests" - specifies and compares standardized methods for assessing bimetallic (galvanic) corrosion of metals and coated metals exposed to natural atmospheres. The standard describes specimen types, preparation, exposure, evaluation and reporting, and explains how to derive the bimetallic effect (a relative measure of corrosion due to contact between different metals).
Key topics and technical requirements
- Scope: Tests are for metals and coated metals in outdoor/atmospheric exposure to determine the amount and type of corrosion caused by metal-to-metal contact.
- Methods compared and described:
- Rectangular plates - allows evaluation of mechanical properties.
- Washers - unique advantage: you do not need to know the anode in advance.
- Wire-on-bolt - shorter exposure (table indicates >90 days possible) and referenced to ASTM G116 for full details.
- Specimen types: test, reference, standard and control specimens and requirements for marking and number of specimens.
- Evaluation methods:
- Mass loss (primary quantitative method).
- Visual examination and mechanical property testing (where applicable).
- Calculation of the bimetallic effect by comparing contacted specimens with reference specimens not subject to galvanic contact.
- Exposure duration & sensitivity: Rectangular plates and washers typically require ≥1 year exposure for full sensitivity; wire-on-bolt can give useful results in shorter periods under certain conditions.
- Important considerations: atmospheric bimetallic corrosion is often localized (typically within about 0.5 cm from contact); a high galvanic potential does not always mean a high corrosion rate - site corrosivity classification (e.g., ISO 9223) is recommended as complementary information.
- Documentation: test report requirements and normative references (ISO 8407, ISO 8565, ISO 9223 referenced; ASTM G116 cited for wire-on-bolt).
Applications and users
- Practical use for materials engineers, corrosion specialists, coating manufacturers, quality control and R&D teams assessing galvanic compatibility of dissimilar metals in outdoor structures.
- Common applications: evaluation of fasteners, cladding/coating systems, joined assemblies, and any situation where bimetallic corrosion may affect service life of infrastructure, building facades, vehicles, and marine/industrial installations.
- Useful for selecting compatible materials, validating coatings, and supporting failure analysis and specification writing.
Related standards
- ISO 9223 (atmospheric corrosivity categories)
- ISO 8407 (removal of corrosion products)
- ISO 8565 (atmospheric corrosion testing)
- ASTM G116 (wire-on-bolt practice - referenced for full wire-on-bolt procedure)
Keywords: bimetallic corrosion, galvanic corrosion, atmospheric exposure, ISO 7441, EN ISO 7441:2015, corrosion testing, rectangular plate test, washer test, wire-on-bolt, mass loss evaluation.
