Overview
ISO 23669:2022 is an international standard that specifies requirements for testing additively manufactured (AM) metals and alloys to determine their susceptibility to localized corrosion and environmentally assisted cracking (EAC) in aqueous environments. This document addresses the unique challenges presented by additive manufacturing processes-such as microstructural heterogeneity, residual stresses, and surface conditions-and establishes comprehensive guidelines for designing test specimens, conducting corrosion and cracking tests, and reporting results.
The standard ensures consistent evaluation of corrosion resistance and cracking performance of AM metals, supporting safety, reliability, and longevity in industrial applications where corrosion can compromise structural integrity.
Key Topics
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Additive Manufacturing Challenges
AM processes produce complex microstructures due to layer-wise building, with variations in grain size, elemental segregation, residual stress, porosity, and anisotropic properties. ISO 23669:2022 requires detailed material characterization to capture these factors before corrosion testing.
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Material Characterization
Testing requires samples taken after post-processing, such as thermal treatment or machining, that represent the material surface exposed in service. Critical parameters include:
- Microstructure orientation relative to the build direction
- Grain size and phase distribution
- Porosity measurement using metallography or X-ray computed tomography
- Residual stress assessment using techniques like X-ray diffraction
- Surface roughness profiling comparable to the final product condition
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Tensile Properties Assessment
Tensile testing as per ISO 6892-series standards must be conducted to measure properties like proof stress, ultimate tensile strength, and elongation. These data support understanding of mechanical behavior influencing environmentally assisted cracking resistance.
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Localized Corrosion Testing
Methods such as double-loop electrochemical potentiokinetic reactivation, critical pitting temperature measurement, and potentiodynamic polarization are prescribed to:
- Assess sensitization, particularly for alloys like stainless steel
- Evaluate pitting and crevice corrosion susceptibility with realistic surface finishes mimicking end products
- Address orientation effects by testing surfaces built in different AM directions (X/Y and Z planes)
- Incorporate multiple test repeats to account for variability due to AM defects
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Environmentally Assisted Cracking Tests
The standard defines requirements for specimen preparation and testing to investigate EAC initiation and propagation influenced by environmental exposure and residual stress.
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Test Reporting
Detailed documentation of material conditions, test procedures, specimen orientation, surface finish, and statistical analysis of results is mandated to ensure reproducibility and meaningful comparison between AM materials.
Applications
ISO 23669:2022 is critical for industries utilizing additive manufacturing of metal components that operate in corrosion-prone environments such as:
- Aerospace and aviation
- Automotive manufacturing
- Oil and gas extraction and refining
- Marine and offshore structures
- Chemical processing plants
- Medical device manufacturing
By adhering to this standard, manufacturers and researchers can:
- Evaluate corrosion resistance and cracking risk of novel AM alloys
- Optimize post-processing and heat treatments to enhance durability
- Support certification and regulatory compliance for safety-critical components
- Reduce unexpected failures due to environmental degradation
- Accelerate material qualification cycles during product development
Related Standards
ISO 23669:2022 complements and references several key international standards, including:
- ISO 6892-1 & ISO 6892-2: Tensile testing methods at room and elevated temperatures
- ISO 7539 series: General guidelines for stress corrosion testing and specimen preparation
- ISO 8044: Corrosion vocabulary
- ISO 15158: Measurement of pitting potential for stainless steels
- ISO 12732 and ISO 3651-1: Tests for sensitization of stainless steels
- ISO 17864: Determination of critical pitting temperature
- ISO/ASTM 52900 & 52921: Foundational terminology and methodologies for additive manufacturing
- ISO 18089: Crevice corrosion test methods
These standards collectively establish a robust framework for assessing corrosion and cracking resistance of metals, with ISO 23669:2022 specifically addressing the nuances related to additively manufactured materials.
By implementing ISO 23669:2022, stakeholders can ensure comprehensive, consistent, and reliable testing that addresses the advanced material characteristics unique to additive manufacturing, thereby enhancing product quality and lifecycle performance in corrosive environments.