Overview
ISO 22848:2021 specifies a standardized laboratory test method to determine the stress corrosion crack (SCC) growth rate of steels and alloys under static-load conditions in high‑temperature water (for example, environments simulating light water reactors). The method monitors crack length in a fracture‑mechanics specimen using a potential drop method (PDM) while the specimen is held in an autoclave. The standard applies to stainless steels, nickel‑base alloys, low‑alloy steels, carbon steels and other alloys used in high‑temperature water environments.
Key topics and requirements
- Test principle: Continuous measurement of crack growth (da/dt) under static load to determine SCC growth rate as a function of stress intensity factor (KI) and environment.
- Specimen preparation: Guidance on specimen orientation, geometry (commonly compact tension (CT) or contoured double cantilever beam (CDCB)), surface finish, dimensions and measurement of initial/final crack length.
- Crack initiation and transitioning: Procedures for fatigue pre‑cracking, SCC transitioning (using low‑frequency cyclic loading with increasing hold times), and crack‑tip re‑activation loading if crack retardation occurs.
- Crack monitoring: Use of the potential drop method (PDM) to continuously track crack length inside the autoclave; measurement of corrosion potential.
- Test environment and equipment: Requirements for autoclave installation, water chemistry control and monitoring (relevant to simulated BWR/PWR environments), and recommended test apparatus (see informative annexes).
- Data evaluation and reporting: Methods to calculate SCC growth rate, crack engagement, average/min/max crack extension, and required content for the test report.
- Informative annexes: Include CDCB geometry and KI calculations, equipment recommendations, water chemistry monitoring items, and an approach to determine crack growth rate.
Applications and users
ISO 22848:2021 is intended for:
- Corrosion and materials engineers assessing SCC susceptibility and crack growth behavior of candidate alloys.
- Nuclear industry laboratories qualifying materials and welds for light water reactors (PWR/BWR) where high‑temperature water SCC is a concern.
- Research institutions studying environmental and mechanical factors that influence SCC.
- Failure analysis and qualification labs performing comparative testing, lifetime assessments, and regulatory submissions.
Practical uses include material selection, weld procedure evaluation, pre‑service and in‑service testing, and R&D into mitigation strategies for SCC in reactor components, piping and pressure vessels.
Related standards
- ISO 7539‑6 - referenced normative standard for preparation and use of precracked specimens for constant load or constant displacement SCC tests.
- ISO 22848 complements other corrosion and fracture mechanics standards for consistent SCC testing and reporting.
Keywords: ISO 22848, stress corrosion cracking, SCC growth rate, potential drop method, high‑temperature water, light water reactors, autoclave, compact tension specimen, corrosion testing, stainless steel, nickel‑base alloys.