Overview
ISO 4680:2022 - Corrosion of metals and alloys - Uniaxial constant-load test method - defines a laboratory procedure to evaluate the susceptibility of metals and alloys to stress corrosion cracking (SCC) in high‑purity water at high temperatures. The method is tailored for simulated primary water environments of light water reactors (LWRs) and specifies uniaxial constant‑load testing under controlled chemistry, temperature and pressure (temperatures above the boiling point of water at normal pressures). The standard covers specimen design, test apparatus (autoclave, loading mechanism, circulating loop), monitoring methods and test reporting.
Key topics and technical requirements
- Test principle: apply a constant uniaxial load to specimens in a controlled high‑purity water environment and evaluate SCC by time‑to‑initiation, time‑to‑failure, extent of cracking or electrical resistance changes.
- Specimens: guidance on specimen categories, shapes (rod, plate, tubular), orientation, surface finishing, machined notches and weld/weld heat‑affected zones.
- Test apparatus: requirements for loading fixtures, autoclaves, circulating loops and instrumentation for corrosion potential and temperature control.
- Environment control & measurement: protocols for water chemistry, corrosion potential monitoring and measurement parameters; annexes provide examples for BWR and PWR primary water chemistries.
- Accelerated testing: permitted accelerating factors (without changing crack mechanism) and examples - e.g., addition of sodium sulfate (Na2SO4) or crevice formation for simulated BWR environments, and elevated temperature for simulated PWR environments.
- Monitoring & evaluation: in‑situ electrical resistance methods, crack morphology observation, validity of failure location and other evaluation indices.
- Safety & reporting: safety warning for hazardous operations and a detailed test‑report checklist (see informative annexes).
Practical applications and users
ISO 4680:2022 is intended for:
- Corrosion and materials engineers conducting SCC susceptibility testing and materials selection for nuclear and high‑temperature water systems.
- Nuclear industry laboratories validating components and materials for LWR primary systems (BWR/PWR).
- R&D organizations and failure analysis teams assessing comparative SCC resistance of alloys, weld metals and heat‑affected zones.
- Regulators and plant operators specifying qualification tests and interpreting accelerated SCC data for life‑assessment.
Use cases include material qualification, comparative screening of alloys, investigation of SCC initiation mechanisms, and validation of mitigation measures.
Related standards
Keywords: ISO 4680:2022, stress corrosion cracking, SCC testing, uniaxial constant‑load, high‑purity water, LWR, PWR, BWR, autoclave, accelerated testing, Na2SO4, crevice, materials testing.