Overview
EN ISO 7539-10:2020 (ISO 7539-10:2020) specifies the reverse U-bend (RUB) method for stress corrosion testing of metals and alloys. The standard defines procedures for designing, preparing and using RUB specimens to investigate susceptibility to stress corrosion cracking (SCC). Primarily intended for high corrosion‑resistance materials (for example Ni‑based alloys), the RUB test is a severe screening technique that imposes high tensile stresses with reduced stress relaxation compared to conventional U‑bend or C‑ring methods. The document is published by CEN as EN ISO 7539-10:2020 and forms part of the ISO 7539 series on corrosion testing.
Key topics and technical requirements
- Specimen types: Half‑tube specimens from tubing/piping, or semi‑circular specimens formed from plate, bar or welded products.
- Preparation: Cut without altering material properties, machine to dimensions, deburr and finish by coarse‑to‑fine grinding to a surface finish such as P600. Final heat treatments (if used) must be performed before reverse U‑bending.
- Reverse U‑bending process: Two‑stage stressing - bending followed by fastening with a loading bolt to maintain high initial tensile stresses over the inner surface. Elastic stress relief must be avoided during fastening.
- Testing procedures: Guidance for multiple or serial immersion exposures under simulated service conditions to accelerate SCC.
- Post‑exposure evaluation & reporting: Visual and metallurgical evaluation of specimens, and standardized test report items to ensure reproducibility and traceability.
- Safety note: The standard warns of hazardous materials and procedures; users must adopt appropriate health and safety practices.
Applications and who uses it
- Primary use: Rapid screening of tubing, piping, plate, bar and welded components for susceptibility to stress corrosion cracking.
- Users: Materials and corrosion engineers, metallurgists, quality assurance laboratories, R&D teams, and manufacturers of high‑performance alloys and components (especially in oil & gas, power generation, chemical processing, and aerospace).
- Purpose: Material selection, comparative evaluation of alloys, acceptance testing (by agreement), and failure‑mode investigation under simulated service environments.
Related standards
- ISO 7539-1 - General guidance on stress corrosion testing procedures (normative reference).
- ISO 8407 - Removal of corrosion products from test specimens (normative reference).
- The RUB method is part of the broader ISO 7539 series addressing stress corrosion testing of metals and alloys.
Keywords: reverse U-bend, RUB, stress corrosion testing, ISO 7539-10, EN ISO 7539-10:2020, stress corrosion cracking, corrosion of metals, tubing testing, specimen preparation.
